tag:blogger.com,1999:blog-86660912019-07-18T07:38:56.044+02:00The Reference FrameSupersymmetric world from a conservative viewpointLuboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.comBlogger1150125tag:blogger.com,1999:blog-8666091.post-47269866809329050692019-07-16T08:27:00.002+02:002019-07-16T09:10:01.622+02:00Strings 2019 wasn't a comprehensive string conferenceThe main reason I didn't want to write about <a href="https://sis-pc15.ulb.ac.be/event/2/">Strings 2019</a> in Brussels (July 9th-13th) was that I am not thrilled about getting dozens of nasty attacks by moronic crack pot-smoking trolls brainwashed and radicalized by pathetic one-dimensional anti-physics websites combined with the silence of those who aren't idiots.<br /><br /><img src="http://www.new-hotel.com/en/sites/default/files/imagecache/scale_and_crop_970x403/flagey-brussels.png" width=407><br /><br />Another reason is that I didn't see much new that I would overlook during the year – which is probably normal for those of us who diligently follow (not only) hep-th on the daily basis. But after some inspection, it became clear to me that it's not just because of my regular arXiv habits. The conference just didn't really cover most of the stringy craft. The holes were obvious both in the topics and the list of participants.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Look at the list of <a href="https://sis-pc15.ulb.ac.be/event/2/registrations/participants">494 participants</a>. Search for Stanford which is, you know, a powerful string hotbed in the Bay Area. You will find Shenker and Saad – because Douglas Stanford has Stanford as its last name. Add Santa Barbara. Just two participants, Gross and Maxfield. Zero from Santa Cruz. Just one from MIT, Harlow.<br /><br />Princeton gives 18 (IAS+Univ) and Harvard 5 hits, Oxford 7 and English Cambridge 7, reasonable numbers, indeed. They make the absence of California even more striking.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />But the <a href="https://sis-pc15.ulb.ac.be/event/2/timetable/">timetable with talks</a> paints an even more obvious picture of "whole missing branches" of string theory. All of the talks are about some French-speaking style general complexity-thermodynamics-AdS-attempts-on-quantum-cosmology issues, with some CFT rather disconnected from the string vacua. There was also some swampland and the weak gravity conjecture. Some people probably think that I should be happy but I am not.<br /><br />What seems to be missing is the whole "full-blown string industry". Actual vacua in more than 4 dimensions, their stringy/M-theory origin, higher-dimensional field theories, compactifications geometric and non-geometric, what string theory allows you to do with all these extra dimensions and how, string phenomenology, anything that depends on fancier tools where string theory actually becomes a specific theory allowing something but not something else etc. There are lots of perspectives to take to enumerate what is missing but just to make the hole I perceive obvious, let me say that I see<br /><ul><li>no Calabi-Yau or other manifolds</li><li>no type I,IIA,IIB</li><li>zero M-theory, zero F-theory</li><li>one talk with something "heterotic"</li><li>one talk with "D-branes" but the high spacetime dimension etc. isn't the point; no higher-dimensional matrix models</li><li>nothing like <a href="https://motls.blogspot.com/2019/03/one-quadrillion-standard-models-in-f.html?m=1">Cvetič</a> et al. or <a href="https://motls.blogspot.com/2019/06/a-three-parameter-jungle-of-f-theory.html?m=1">Taylor</a> et al. F-theory model building</li><li>well, Vafa wasn't there, and the same holds for "his junior collaborators", I think</li><li>Andy Strominger gave a talk about a self-similar behavior of the photographed M87 black hole, entertaining but clearly not string theory</li><li>nothing like <a href="https://motls.blogspot.com/2019/06/acharya-stringm-theory-probably-implies.html?m=1">Acharya</a> and his proof of SUSY from classification of Ricci-flat manifolds</li><li>two talks have "super" in the titles but almost anything where supersymmetry really matters in some way are missing</li></ul>I could continue for a while. It seems to me that the full-blown stringy industry – which actually depends on some highly nontrivial expertise and tools – has been largely omitted or censored or disinvited or something else. It just wasn't there. 494 people seems like a good standard number of participants but the conference – maybe not the first one – was largely taken by people who aren't primarily string theorists or who aren't full-blown string theorists or at least who aren't focusing on string theory now etc. The topics were correspondingly less dependent on the stringy tools and expertise, were kind of "more generic and accessible for everybody physics", "more philosophical" in the nearly humanities sense. <br /><br />It is just a bad trend. It almost looks like someone was trying to make the conference more compatible with those who aren't really string theorists – or even those who dislike string theory. <br /><br />Experienced TRF readers must be able to predict that I wouldn't be capable of resisting the analogy with something else linked to Brussels: the "multicultural" immigration. Brussels finds it convenient to import lots of easy-to-manipulate people from the Muslim world who are easier to govern because they don't demand "luxurious" things like freedom and democracy and they aren't attached to any European nation state. So it promotes "multiculturalism" which is a euphemism for an uncivilized "monoculturalism" where everything incompatible with Islam is being rather quickly suppressed.<br /><br /><iframe src="https://api.mapy.cz/frame?params=%7B%22x%22%3A4.372898439547356%2C%22y%22%3A50.82689721919521%2C%22base%22%3A%222%22%2C%22layers%22%3A%5B7%5D%2C%22zoom%22%3A17%2C%22url%22%3A%22https%3A%2F%2Fen.mapy.cz%2Fs%2F3vBMe%22%2C%22mark%22%3A%7B%22x%22%3A%224.372898439547356%22%2C%22y%22%3A%2250.82689721919521%22%2C%22title%22%3A%22Flagey%22%7D%2C%22overview%22%3Atrue%7D&width=400&height=280&lang=en" width="400" height="280" style="border:none" frameBorder="0"></iframe><br /><br />The composition of the topics at the string conference looks analogous. The full-blown string theory just doesn't seem to be welcome, appreciated etc. – I would like to know whether these omissions are due to the organizers' ignorance of the field or their malicious intent. The increasing fraction of non-string participants and talks suggests that "everyone" has the right to go do a string conference, much like "everyone" has the right to migrate to Europe. It's totally unhealthy and self-harming. It's existentially dangerous. It's extremely harmful to deconstruct the prestigious character of the string conferences.<br /><br />It almost looks to me as if the nasty anti-string crackpots were co-organizing the conference and could veto talks if not participants.<br /><br /><b>Vision session</b><br /><br />Now, to make similar points in a more specific context, let me discuss a 26-minute-long video<br /><blockquote><a href="https://livestream.com/streaming/events/8742238/videos/193714289">The Vision Session</a><br /></blockquote>Thanks to Francis Villatoro for the link. OK, there are six people on the podium: Gross, Harlow, Seiberg, Alday, Stanford, Arkani-Hamed, from the left to the right. Let's say that three are senior, three are junior folks. In a good approximation, the junior people are those who seem to have all their hair. That's too bad, boys, if you're not <em>naturally</em> senior in this sense, maybe you should at least go skinhead... but Daniel Harlow would probably find it insufficiently politically correct, right?<br /><br />The general feeling is that the junior people don't have any visions. It may be due to design and pressures, due to the selection, due to something else or a combination, but the gap is clear. But let's not be too quick.<br /><br />At the beginning, Nima asks about the unitarity in Stanford's talk. Stanford starts to say seemingly complex boring things about "it depends what you mean by unitarity". OK, I am not familiar with every page of Stanford's papers but I just don't believe that the word "unitarity" has become this muddy. Unitarity is the property of an operator producing some evolution or transformation, \(UU^\dagger=1\), usually combined with the assumption of a positive-semidefinite space on which this operator acts. If there's a Hamiltonian, its Hermiticity is equivalent to the unitarity. Unitarity may require appropriate conditions for the normalizability of the external states etc. But I just don't see the room for all this fuzz. "What do you mean by unitarity?" You should damn know what unitarity is.<br /><br />A minute later, it turns out that Stanford is computing some "averages over theories". You may compute such averages but you cannot <em>live in a world that is averaged over theories</em>. Well, decades ago, Sidney Coleman was trying to create a counterargument with some baby universes etc. but I would insist on my statement. An ensemble is OK but the "theories" must still be considered mutually exclusive and one can still ask whether each of them is unitary or not. So I concluded that the whole paper or talk by Stanford is probably gibberish – assuming some logically inconsistent generalization of quantum mechanics. The "averaging over theories" sounds like some multiculturalism, too. The context where they studied it was apparently the SYK or JT model. They're really toy models where such basic things should be particularly clear. I can't believe that they end up with this fog about the simple question whether the "unitarity" is obeyed by Stanford's talk.<br /><br />At any rate, this foggy technicality has nothing to do with visions in string theory. Gross surely had the same feelings as I just mentioned so around 4:00, he explicitly asked about the desired future according to practitioners who are young i.e. below 35-40. Harlow who was falling asleep in the recent minute seems surprised or shocked by the question. I mean this is a panel about visions about string theory. Why are you there if you are shocked by such a question? Gross said that he surely had clear dreams – masses of hadrons etc. – but the Millennials don't seem to have anything like that.<br /><br />Harlow doesn't know what to say, "it's a recipe for saying things that are wrong". "It's a wish," Gross says instead. You can't really do important science without having wishes, or if you're afraid of saying things that will be wrong. Harlow acts like he is calculating what form of self-consorship will be viewed as the most politically correct one. He has nothing authentic to offer here. OK, he ends up with a lukewarm proposition "I still think string theory is a strong candidate" and "it would be nice to get some support, probably from cosmology". If in 40 years, there's no deep advance like "at least calculating the cosmological constant" (wow, that already counts as a modest plan), Harlow "hopes to work on something else". Perhaps authoring petitions to harm careers of ideologically inconvenient people is Harlow's idea about this "something else"? Other junior folks add some "computable early Universe that would be nice" and move their heads in unexcited ways.<br /><br />Harlow asks Iceberg whether we're just on the tip of a Seiberg, or vice versa, in QFTs, and whether fractons totally revise what QFTs are. Seiberg has lost some sleeps over fractons... but why here and why now? This is a string conference and <a href="https://scholar.google.com/scholar?q=fracton&hl=en&lr=&btnG=Search">fractons have been discussed</a> in condensed matter physics at least since 1983. Some people with a more particle physics background may talk about fractons now – because they're doing things closer to condensed matter in general – but why is it interesting and what does it have to do with visions? Some particle physicists are just joining a topic in an adjacent field that is some 35 years old. I don't find it exciting, I don't consider these joiners "pioneers", and I don't think that fractons are likely to be important for the fundamental laws of Nature.<br /><br />Seiberg doesn't know what fractons are but suggests that several icebergs exist. Seiberg switches to exact solutions of some field theories. Seiberg says one should be as ambitious as possible but also have short-term plans. Alday asks Seiberg whether dualities will be obvious and Seiberg says that dualities must be by definition surprising. Right except that what is surprising to start with may become obvious once you understand more. Seiberg says that a change of variables is by definition "not surprising", I agree with that, too. So the electromagnetic duality is unsurprising in the free Maxwell theory but not in \(\NNN=4\).<br /><br />What about T-duality, is it surprising? It looks surprising in the spacetime but in string field theory, it is a field redefinition – and it is also a "free electromagnetic duality" on the world sheet. So T-duality probably isn't surprising according to Seiberg. But what about the rest of U-duality group in maximal supergravity (which also includes S-duality subgroups)? It may be fully generated by several subgroups isomorphic to T-dualities. The problem is that T-duality was proven above in a weakly coupled limit only. The full U-duality goes beyond that – but it may still be fully proven e.g. in the BFSS matrix model, up to some number of compact dimensions.<br /><br />While never considered a full-blown string theorist, Nima actually fixes the discussion and offers some stringy visions. It could be possible – an advance could be around the corner – to figure out whether the large field inflation is possible or impossible within string theory. Well, we were already working on such things 15+ years ago (a full no-go theorem should have been found before BICEP2, Nima insists). Also, maybe someone should have predicted the discrepancies in the value of the Hubble constant, Gross adds while Nima agrees. Existing models implying the numerous values look like contrived mess.<br /><br />Nima still sees a big gap between "string theory as the unified theory on steroids with a single theory of quantum gravity" and "the picture where every QFT has its dual quantum gravity". We've discussed this dilemma after it was voiced e.g. by Steve Shenker already around 2000. I don't see any big tension here. What is unique is the fully formulated theory but it still has many solutions and the solutions may only become unique or close to unique once you try to minimize the curvature and decompactify as much as possible. So 11D M-theory and five 10D string theories are unique or almost unique but there are many compactifications to 4D etc. – either the regular Calabi-Yau compactifications or theories that may be linked to generic CFTs by AdS/CFT which are generically "Planck radius compactifications". As Nima said in a fresh <a href="https://www.quantamagazine.org/the-simple-math-behind-our-expanding-universe-20190715/">Wolchover's article</a>, the de Sitter symmetry is an asymptotic one for the future – when things flatten out. Flattened things are like "IR limits" and "universal behavior" and they are almost unique while things with lots of curvature become very non-unique and it's actually a pretty good thing. Doesn't it make sense? If you try to decompactify the AdS theories coming from any CFT via AdS/CFT, you still get one of the well-known maximally dimensional string/M-theories.<br /><br />Fine. Nima did mention my answer, showing he was aware of it. It's the compactification and/or high, near-Planckian curvature that brings non-uniqueness. But, he adds, take a 9-dimensional theory with the SU(17million) and a horrible matter content. Is it anomalous? Well, Nima, it doesn't have the usual basic types of anomalies but it's almost certainly in the swampland because string theory implies lots of inequalities etc. In some sense, they come from anomaly considerations, too. Take heterotic strings, the maximum rank of the gauge group is bounded from above, right? It comes from the critical dimension – compactified dimensions increase the rank – and the critical dimension comes from the conformal anomaly. So string theory imposes all kinds of inequalities. The matter content is "bounded" in a way that is morally related to the critical dimension – although, in F-theory, the gauge groups may be really large and numerous. But the Hodge numbers of Calabi-Yau three-folds are probably also bounded. It's a tough mathematical question but there may also be a crisp physical derivation of such mathematical inequalities. Lots of extra conditions like that – you know, the swampland conditions – exist to make sure that even in the absence of knowledge about the precise vacuum, string theory is predictive. But without the information about the particular vacuum, string theory doesn't predict "everything".<br /><br />Gross responds by saying that the Ising model is probably dual to something but who cares? Not all dualities are useful. I agree with that. If we had the full definition of string theory, we could in principle answer this question, but if we don't have the full definition, we can't answer it and I personally don't care because the answer doesn't look important for anything else. The Ising model is either a non-solution of string theory or a solution that is clearly irrelevant for particle physics phenomenology. Is there a big difference between the two? You could add the Standard-Model-like qualitative features as extra conditions on top of equations of string theory, and then the answer would be "it is a non-solution".<br /><br />OK, Gross would still like to see the QCD string. I don't believe there is an illuminating string theory construction that produces the pure QCD. And if there is one, my emotions remain almost as low as in the Ising model case. Gross probably has some extra emotional attachment to pure QCD but you know, David, it's just another toy model for the rest of us, just like the Ising model! <br /><br />I personally don't think that a string vacuum exactly equivalent to the Ising model is an exact solution of string theory. But maybe it is one. We don't have the complete equations of string theory, of course. I don't think that the answer is too important because in physics, we also need at least a conceptual agreement with the reality, like 3+1 nearly flat, large dimensions and gravity. It's only with these additional "experimental" constraints when it's important for string theory's space of solution to become semi-unique, and I find it extremely likely by now that the right vacuum won't be quite unique.<br /><br />The junior people don't seem passionate about any of this.<br /><br />Questions are asked from the audience. New fog emerges about the phrase "equivalence class of QCD". Like in the case of "unitarity", I find it strange that such basic phrases create so much confusion. "Equivalence" is a strong word so all theories "equivalent" to QCD really are QCD (or its hypothetical dual[s]). The man probably meant a wider class but he should have defined it beyond misleadingly simple adjectives such as "equivalence". The phrase "equivalence class" was apparently started by Seiberg and he meant "trivial to solve". What does "trivial to solve" have to do with "equivalence"? Random confusing things are said about random cousins of QCD or their classes. I have no idea how such a chaotic discussion could be inspiring. Gross is generally annoyed that Seiberg expressed the view that QCD was boring, although he tried to soften that, but I do agree that QCD is boring – relatively to things that would be "visions".<br /><br />Witten suggests finding the dual of any confining cousin of QCD, or asymptotically solvable generalizations of \(\NNN=4\) etc. Hmm, there are some intermediate softening of the conditions.<br /><br />An Indian guy asks about hopes to solve the Ramond-Ramond backgrounds of string theory. I personally don't find it conceptually hard. In principle, you may add condensates of all these messy picture-changing operators etc. Also, in Berkovits' pure spinor formalism (and the Green-Schwarz variables in the light-cone gauge, if possible), Ramond-Ramond fields just may be allowed to start with. I don't see RR fields as more conceptual than a technicality that is hard in some particular world sheet variables – but still doable in a weakly coupled string theory. Gross says that we understand the \(\NNN=4\) holographic dual of a Ramond-Ramond background. Right.<br /><br />A question was asked about non-locality in string theory, mentioning Ashoke's talk. Sen's violation of locality wasn't due to local non-analyticities but due to some behavior in the whole complex plane, Gross argues. Harlow mentions AdS/CFT as a striking non-perturbatively created non-locality of bulk AdS theory – the non-locality coming from the string interactions is even enough to change the target space dimension. I agree with that.<br /><br />Aside from commenting on some technicalities, the Millennials don't seem to have visions.<br /><br />A few vague comments about the computation of parameters. Gross thanks for great talks, dance, and the food. Maybe they also drank urine from the little pissing boy of Brussels, it had to be delicious.<br /><br />OK, to wrap up this display of the murder of the passions and enthusiasm, I think that the field is being systematically diluted, stripped of its concentrated flavor, self-confidence, prestige, renaissance men, and of its dreams about the future. I think it's mostly being done by pressures from outside – combined with the absence of balls inside (especially because I think lots of excited people still do full-blown string work but they weren't participating at the conference at all, so the "organizers" tend to amplify harmful trends) – and it's a model for what is happening with the whole Western civilization. The political correctness is what is ruining both – string theory as well as the Western civilization.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-50427301574709072352019-07-09T13:32:00.001+02:002019-07-09T17:45:23.676+02:00Vafa, Ellis debate with a bright religion scholarMarkusM has pointed out that a more pleasant, entertaining, and physics-oriented public discussion took place in recent days, in the Institute of Art and Ideas (iai):<br /><blockquote><a href="https://www.youtube.com/watch?v=NGH8Rt_SNy8">Does the Multiverse Exist? | Full Debate</a> (43 minutes)<br /></blockquote>Participants were Harvard's string theorist Cumrun Vafa whom I know very well, you know, CERN's phenomenologist John Ellis, and an assistant professor of religion, feminism, gender, and sexuality Mary Jane Rubenstein of Wesleyan University. Religion and feminism is quite a combination – maybe she hasn't noticed yet that according to religion, feminists will burn like brown coal in the hell for the eternity (because of the eternal character of the oxidation, feminist corpses in hell count as a renewable energy source). As we will see, she was the nicest surprise of that event.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Cumrun started by mentioning he was convinced string theory was a theory of Nature, also because it has allowed us to calculate the precise entropy of black holes – he modestly overlooked the fact that it was he and Strominger who pioneered this amazing sub-industry.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Near the beginning, the charming and talkative Ms Rubenstein started to talk a lot. For a few sentences, I thought: She must be a lady who likes to talk and her greatest intellectual achievement was to learn how to pronounce the word "epistemologically" which she really likes. But the following minutes have changed my mind profoundly. She has presented a long monologue – although with some notes – about the constants of Nature, quantum field theory, interesting and uninteresting types of the multiverse, and so on.<br /><br />So I obviously concluded: This is not a normal behavior for a religion-and-feminism professor. She must have a coach who is a physicist because most of the stuff she said – including the radius of the visible Universe at over 40 billion light years, something that even many enthusiastic fans of physics get wrong – was totally correct and nontrivial. Well, she also suggested that nobody loved the ekpyrotic or cyclic Universe (correct) and that mathematics makes the many worlds interpretation of quantum mechanics inevitable (incorrect).<br /><br />I started to think. Well, she has a physics coach but I must be capable of saying even more, right? I decided that the coach has to be Brian Greene, especially because her monologues was overlapping so much with the Hidden Reality, a book by Greene that I also translated to Czech, a decade after The Elegant Universe. So I have made a prediction: It will be easy to find Rubenstein and Greene on the same places. This prediction has passed some tests (she wrote a book heavily referring to Greene) so now I am willing to bet a lot that she would agree that she got most of her physics and cosmology from Brian Greene.<br /><br />Although her monologue was interesting, she was largely ignored. Instead, the host David Malone had a lot of fun with the claim that there were 10<sup>500</sup> Universes. Cumrun said it was an underestimate – because the total number of vacua was clearly infinite (just take the AdS5 x S5 vacua of type IIB at all allowed radii for an infinite set!) – which the host found very entertaining.<br /><br />It's cute when children laugh. You present something and a schoolkid tries to see a penis in every sentence (about amino acids, for example). You may enjoy it as well but you quickly realize it is silly. There is nothing to laugh about here. <br /><br />It is very clear why the host is laughing – because he is another irrational layman who finds a "very large number of solution" to be a terrible thing – laymen are generally terrified by mathematics, numbers, and especially by large numbers. But there is nothing terrible about it at all. An equation or a theory has some set of solutions. The number of solutions is a non-negative number, an integer or infinity, and it is whatever it is. If we can't prove that a particular value is correct or other values are incorrect, then all values are equally acceptable. It is completely irrational to be biased against any solution. And it is just childish to laugh when someone determines that the right number is a large constant or infinity.<br /><br />Incidentally, the host also said<br /><blockquote>10<sup>500</sup> is ten followed by 500 zeroes.<br /></blockquote>Not really. It is ten followed by 499 zeroes! ;-) The normal people say it is one followed by 500 zeroes.<br /><br />OK, I thought that this laughter of ignorance by the host wouldn't be addressed at all even though it's really a crucial point here. But it happily did get addressed. I am not sure whether it was a lucky coincidence or someone's grander plan. John Ellis introduced himself. Much of the attraction to string theory is about symmetries – string theory is the queen of symmetries. I actually disagree with that (string theory suppresses the role of symmetries in many ways, and also bans any global symmetries) but in the context of these conceptual discussions, it is a detail because the character of string theory's beauty is <em>analogous</em> to the beauty of the symmetries. Ellis said many things about himself and why he chose to be a man who applies the symmetries.<br /><br />Soon afterwards, he said that Cumrun has pioneered something relevant for this discussion, the swampland. Not everything is allowed. So Cumrun could convey the point that while 10<sup>500</sup> or infinity are large numbers, they don't mean that "anything goes" within string theory. Not so fast. So many things could be possible within effective field theory – like vacua where gravity is stronger than the other forces – but they are forbidden in Nature. They don't really exist.<br /><br />By being forbidden in Nature, Cumrun meant "forbidden by the constraints implied by string theory". Of course it's the same thing in his picture of the world because he assumes and believes that Nature is described by string theory. Nevertheless, it was immediately turned into a controversy. Ellis added "according to string theory" to Vafa's words and the host started to laugh like a naughty schoolkid again. To make things worse, the host said he wanted to "sidetrack" a little bit: it sounds just like the anthropic principle.<br /><br />Holy cow. It doesn't. It's really the opposite. Cumrun wants to show that good old physics constraints decide while the anthropic principle is basically the assumption that physics doesn't matter and the existence of intelligent animals is what constraints the choice of our vacuum or vacua. So the host wanted to "confirm" he's getting it and Cumrun informed him that "not really".<br /><br />Also, I find it bizarre that the host vigorously tried to shut down a discussion about the anthropic principle – in a discussion whose title is "does the multiverse exist". Why would you shut down the discussion about this closely related proposed principle in a discussion that claims to be dedicated to the multiverse? The multiverse and the anthropic principle aren't the same thing but they're often discussed together and this is what a discussion about the multiverse should also clarify.<br /><br />OK, this ban didn't succeed and around 14:10, Cumrun tried to communicate a simple point that he's not a defender of the anthropic principle. The host interrupted him with a would-be witty "you're in the swampland". It's a little bit witty because I have laughed but the real reason why I laughed is that it is so cutely dumb. The anthropic principle isn't the opposite of the swampland in any sense. It's clear why the host made the not so intelligent remark. Because the landscape is "equivalent" to the anthropic principle, and because the swampland is said to be the opposite of the landscape by Vafa, the swampland has to be opposite to the anthropic principle. So the anthropic principle's foe Dr Vafa has to be in the swampland.<br /><br />The only problem is that the conclusion is wrong and this whole reasoning is totally illogical. The swampland and the landscape are two disjoint sets of <em>models</em> according to a particular kind of reasoning, Vafa's reasoning (or his project to classify theories), but the anthropic principle and old-fashioned-swampland-like reasoning are disjoint in a completely different way. They don't describe two disjoint classes of models. Instead, they describe unequivalent methods how to use the landscape (I wrote these words before I heard Cumrun saying virtually exactly the same thing!) or how to search for the right models.<br /><br />I could see in Cumrun's eyes that he was getting somewhat anxious. Is it possible to explain these things to somebody who apparently believes that "if you're not a fan of the anthropic principle, then you're in the swampland?" ;-) You can't be in the swampland, only quantum field theories may be in the swampland, and real people can't be in the swampland because nothing in the swampland is "real". If the host can't get this point, can he get anything that matters?<br /><br />Around 14:40, Cumrun protested against the claim that "mathematics isn't interesting, who cares" etc. Our disobedient happy schoolkid began to laugh again! The reason behind his laughter is his ignorance but at least I found his laughter somewhat contagious, like the laugh track in the Big Bang Theory, so that has improved my experience.<br /><br />Mathematical consistency etc. can lead us a huge distance towards the future. Maxwell is an example, Vafa said. Maxwell has added a term just to make the equations consistent and the conclusion was that he could predict the moving electromagnetic waves. These comments have clearly made no impact on the host's understanding of mathematics and the Universe. But I am confident that some people in the audience were smarter than the host.<br /><br />Rubenstein sort of intelligently said that there were two types of physicists in the search for the Universes. The likes of Cumrun look at the possibilities and their probabilities and don't care about the "existence". Well, Cumrun protested because that's exactly what he doesn't do. He doesn't try to find a probabilistic distribution. Well, he has also written some papers about the Hartle-Hawking states but it's not his dominant approach. So ironically, Cumrun's swampland conditions are really conditions of the Yes/No type, so they are about the "existence" which is exactly what Rubenstein tried to describe as the non-Cumrun approach.<br /><br />OK, where did this misunderstanding come from? A minute later, Rubenstein explained what she meant by the second group. Folks like Penrose who see, in their hopeless papers, stargates into actual other Universe in some patterns drawn in the CMB. ;-) OK, you can't blame Cumrun or me for not predicting that this is what she would call the "second group". It's just some very particular, wrong, single, nutty paper, and it's in no way "a complementary school of thought" to either the swampland or the anthropic principle. OK, I found the spontaneous verbal explosions by that religion-feminist professor sort of cute although, unsurprisingly, she didn't always understand what she was talking about at the end.<br /><br />Her "I think it's totally fascinating, I am thrilled" at 17:15 made me smile. She has a lot of the physicist's enthusiasm. She reported that she doesn't know whether we will ever come to any certainty about the existence of the other Universes. Right, we can't be sure about that.<br /><br />Ellis says that the switch to 10<sup>500</sup> or more Universes represents a tremendous progress because those questions were out of reach some 50 years ago when people couldn't dare to discuss questions about the other Universes. Right. Needless to say, the schoolkid laughs again. It really looks like the defense of contemporary physics has the same effect on him (and not only him) as if you were saying some obscene jokes. But Ellis wanted to throw "stone in Cumrun's direction". The accelerated expansion seems incompatible with string theory. Cumrun: "No, who said that? Which colleagues said that?" Everyone laughs, the host generously allowed Cumrun to hunt them down later. I think that Cumrun knows well who should be hunted here – the #1 wanted man – claiming that string theory bans de Sitter – is named Cumrun Vafa. ;-) Of course, he would say it's not true because he believes in quintessence instead of the de Sitter spaces. When asked about the future of the Universe, Cumrun said it was wonderfully exciting but not one with a happy ending.<br /><br />The host just increased his IQ by 15 points and mentioned that mathematics had a good track record and that's how Dirac, with some extra coffee at night, discovered antimatter.<br /><br />John Ellis bragged that he has coined the term "a theory of everything" – it's OK to boast because it's no longer a popular term – and he liked predictions. String theory was blamed for not having them and that's one reason why Ellis likes Vafa and the swampland – these claims make string theory falsifiable.<br /><br />Why did the multiverse become popular and it's not just science, is it? Rubenstein recalled the various chapters of Greene's Hidden Reality about the types of the multiverses. She totally correctly said that the multiverse exploded around 2000. Right, that's when string theorists took it to explain the recently observed acceleration of the cosmic expansion (in 1998, she even knows this year!). It was really a trend that many if not most string theorists joined at that time. My only paper focusing on the anthropic principle (negatively) was also released in 2000. She discussed lots of details historical facts about Vilenkin's and Weinberg's ringing telephone etc. I am really impressed. At least as a reader of the popular books, she has done her homework extremely well.<br /><br />Nevertheless, Cumrun had to point out that the anthropic principle – the methods to use the landscape – may be incorrect but that doesn't mean that the landscape or the string theory framework is incorrect. Precisely. When asked who imposed the multiverse on Cumrun, he said that the multiplicity of solutions had been known independently of Weinberg and his anthropic principle. Happily, all agree. This multiplicity was helpful for Weinberg to use it.<br /><br />Vafa said a few more things, the host asked Ellis what Vafa meant by "checking". Ellis sort of didn't answer but began to explain the quintessence, which should have been explained some minutes earlier. Now an expectation of many string theorists – possibly testable by telescopes. The host, a testability cop, suddenly expressed his satisfaction. This is how a majority of the laymen around these discussions seem to operate. They seem to insist that they understand some experimental tests, otherwise they consider the science illegitimate. It's really a wrong and harmful attitude and Cumrun tried to convey why but the host hasn't gotten it. Too bad, most of these laymen who have been turned into "testability cops" don't see that they have been brainwashed by some really crappy, deluded, and self-serving demagogues.<br /><br />The host said that 98% of the room was dark energy. LOL, not really. First, it would be just 68% (and 95% when dark matter is added). Second, it's the average over the Universe and in the room, the air is vastly heavier than the dark energy because matter – instead of dark energy – is concentrated around Earth, as Ellis informed him. ;-) You may always learn some cutting-edge new insights, e.g. that there is matter around Earth.<br /><br />Ellis wanted to return to the question why the multiverse was popular – especially among non-physicists. They are probably unhappy with their Universe and they also feel that other people live in another Universe LOL (Rubenstein: it's called the U.S., the host wisely terminated these political ramifications). The host asks Rubenstein: What should the chaps be looking for? Now, Jane has the power to decide about the future of physics. ;-) At 30:13, she actually pronounces the name of Brian Greene for the first time LOL. There has to be evidence, she quotes him (he is surely not the guy who invented that sentence). Before that, Ellis mentions that there's not one lamppost but 10<sup>500</sup> lampposts. Rubenstein correctly notices that when the CMB is used as a key source of evidence, people have different interpretations for blips so there is an interpretational problem. She wants to return to the question what is the primary question. I am not sure that her proposal will fix anything.<br /><br />Vafa gives an answer to Rubenstein's question. Physicists want to understand patterns and know whether the Universe is natural or not etc. Rubenstein says that these "why" naturalness questions push physicists to the realm of metaphysics. Well, you may say that but "metaphysics" may still be done scientifically and rationally or unscientifically or irrationally. What is "metaphysical" about these questions is that they are deep and far-reaching. But depth is something completely different than the lack of scientific rigor. Physics has <em>really</em> advanced far enough that it is credibly and rationally dealing with questions that used to seem to be beyond science some 50 years ago.<br /><br />Ellis opines that physicists do "when where what" and not "why". OK, I disagree with that. A huge portion of physics is about "why" questions. You can't really live without the question "why", as a TV commercial with Gell-Mann concluded. In effect, Ellis later translated many "why" questions to "what are we" and "where did we come from". Also, "where are we going with the whole Universe" completes the list of questions that make Ellis come to work every day.<br /><br />Ellis also explains his "opportunism" – looking for questions where some progress can be made right now. Right. A good choice of the research projects actually is affected by the recent successes and what has become a promising route because of them. Many laymen don't get this point, either. They think that the right questions for science are independent of time. So they're drowning with these clichés and medieval questions that are disconnected from any actual progress that was taking place in the recent years or century.<br /><br />The host turned to Rubenstein and Ellis: How much comfortable do you feel with this heretic, Vafa, who pays attention to the elegance of the equations? Instead of abusing the opportunity to burn Vafa at stake, the religion professor intelligently said that "true" or "real" or "existent" has various forms – existence in the realm of possibility of mathematical ideas, or some real physical evidence. She predictably yet cleverly mentions Plato (and Tegmark, another chapter in Brian's book). Vafa is relieved that the host's plan to execute Vafa didn't work and he friendly interacts with Rubenstein.<br /><br />Vafa reports that string theory has taught us much more than what we expected – something about the Standard Model – such as holography and properties of black holes. The connections of string theory with the known, observed physics and patterns seem way too numerous and encouraging so that it would be a shame not to study the consequences of the theory, and that's what we are doing. It's work in progress, perhaps with many centuries to go.<br /><br />But the approach "string theory is too hard so let's only do simple things" is not what the human beings do, it's not what the theoretical physicists do, but to overestimate what we can do is also wrong. So we are making finite steps but nonzero steps. Exaggerations may be made and are being made in both directions. String theorists aren't claiming to have everything but they do claim to have more than nothing. It make take years or centuries but to stop wouldn't be good for humanity.<br /><br />Excellent, Cumrun. The disobedient kid didn't even get an opportunity for his laughter now. ;-)<br /><br />OK, the host asked a somewhat incomprehensible question about Vafa's opinion on the relationship between the mathematical and physical reality. Vafa pointed out that the host had excessively naive assumptions about how the "physical reality" may be defined. There may "exist" other Universes although it might be possible to prove that no interactions between the components of the world can exist. The word "reality" may be subtle, especially once you allow the multiverse. Right.<br /><br />Cumrun repeats that the "physical reality" isn't sufficiently defined and the host seems disgusted by this observation. But thankfully, the religion professor is really on the same boat with Vafa here – in fact, she started with this theme. OK, Cumrun still complained that her usage of "reality" is also ambiguous. I think that she hasn't really claimed otherwise. She has helped to classify the types of "reality" into some basic groups and deserves the credit for it. At the end, she rightfully suggested she was on the same frequency with Cumrun.<br /><br />It was one of the best debates on current theoretical physics involving people with different backgrounds. And Rubenstein was one of the most well-informed people from the "humanities" when it came to theoretical physics whose monologues I have seen for years if not ever. You wouldn't have guessed that I would praise a "professor of religion and feminism" in this way but it just happened to be the case. She was clearly smarter and less naive than the male host but at least, his not very intelligent choices when to laugh have provided the debate with some contagious laugh track. ;-)<br /><br />I think that at the end, there is a reason why a religion professor looks more intelligent in these debates than many irreligious philosophers and babblers. For centuries, natural science seemed to be a technical branch of the "materialist philosophy" but it simply ceased to be the case sometime during the 20th century. The rise of quantum mechanics – and the materialists' lack of will to admit that facts must be specified relatively to an observer – is the greatest example of the "fall of materialism" in physics. But it's not the only one. The host is a chap who really believes in some "naive materialism". The table is real, it's simple to divide things to real and unreal, everything must be simple like that, and when it's not, he doesn't believe it. But it just doesn't work like that and attempts to enforce a table-like science on modern physics are purely harmful. A religion scholar – who deals with principles of the Bible as well as religious myths – unsurprisingly has a greater understanding for the subtleties of the word "existence" or "reality".Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-59711641857365201242019-07-09T08:20:00.001+02:002019-07-09T10:41:38.704+02:00A frustrating Guardian discussion on string theoryOn June 28th, The Guardian's Ian Simple invited David Berman, a very good string theorist whom I know, and Eleanor Knox – both of them did great – to discuss the question<br /><blockquote><a href="https://www.theguardian.com/science/audio/2019/jun/28/what-happens-when-we-cant-test-scientific-theories-science-weekly-podcast">What happens when we can't test scientific theories?</a><br /><br /><audio class="wp-audio-shortcode" id="audio-2327-1" preload="none" style="width: 100%;" controls="controls"><source type="audio/mpeg" src="https://flex.acast.com/audio.guim.co.uk/2019/06/26-34602-gnl.sci.190628.gj.what_happens_when_we_cant_test_scientific_theories.mp3" /><a href="https://flex.acast.com/audio.guim.co.uk/2019/06/26-34602-gnl.sci.190628.gj.what_happens_when_we_cant_test_scientific_theories.mp3">https://flex.acast.com/audio.guim.co.uk/2019/06/26-34602-gnl.sci.190628.gj.what_happens_when_we_cant_test_scientific_theories.mp3</a></audio><br /></blockquote>Just to be sure, a good scientist tries to extract evidence in clever ways and hard work, whether easy tests in a foreseeable future look possible or impossible. And indeed, easy tests of string theory look impossible – and have looked impossible in the recent 50 years. When asked about the progress in the future which nobody can know, otherwise it would take place now, they were sketching a century – or thousands of generations – of efforts. <br /><br />It's possible that people need this much time. It's possible it won't be enough. It's possible that mankind will turn into hopelessly stupid apes again. But it's also possible that the progress could be faster. Clearly, the estimates how quickly a theory of everything is going to be found depends on the recent advances and their extrapolation – on the people's enthusiasm and self-confidence which, in the case of intelligent people, reflects some actual facts or experience. That's why sensible people such as Witten found it totally possible in the mid 1980s or mid 1990s that the theory of everything would be completed within weeks.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />While Eleanor and David did great, the whole podcast was framed as a modern "trial against Galileo". Throughout the show, the actual scientists were expected to defend themselves and apologize. I find this basic formatting absolutely unacceptable. It is just another manifestation of the political correctness that has run amok.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Aside from David and Eleanor, Sample (remotely) invited a well-known "vanilla critic" who clearly had nothing to say about string theory whatsoever because he knows virtually nothing and couldn't possibly get a well-deserved passing grade in the first undergraduate string theory course. That stuttering, unpleasant vanilla critic was only repeating hostile clichés "it is not science", "it is not testable" etc.<br /><br />String theory unquestionably <em>is</em> science and it is in principle testable. What is't scientific are Inquisition trials where scientists and their theories are being attacked by brute force, without any legitimate technical arguments whatever.<br /><br />The real systemic problem isn't one of the three participants who clearly contributes nothing. The real systemic problem is that Ian Sample, the host, was basically standing on that wrong side in much of his monologues. In effect, there were two plaintiffs and two defendants at this Inquisition trial. So at the very beginning, we learned from Sample that string theory was "controversial" and that no evidence in favor of string theory has been found in 35 years. What? What the hell are you talking about, Sample? 2019 minus 35 is equal 1984 – which is not only the Orwellian year but also the year when the First Superstring Revolution Started. <br /><br />A majority of the evidence in favor of string theory has been found after 1984.<br /><br />As David and Eleanor were trying to explain – but too politely, so that Sample couldn't get it – the evidence that assures competent physicists that string theory is here with us to stay has a more complicated, mathematical form than what unrefined minds such as Ian Sample's can comprehend. Everyone who has tried to look into this question but concluded that "no evidence in favor of string theory has been found for decades" is simply an intellectually inferior person who is incapable of becoming a theoretical physicist in 2019. The statement is demonstrably wrong – spectacularly wrong – but only smart people may understand the proof. <br /><br />What is so difficult about this simple point? What is difficult is that it is politically incorrect – all the people who have no chance to understand the contemporary science because they are too stupid must be considered as "equal", anyway. Well, they are not equal. What they have to say about science is smaller than what string theorists have to say by many orders of magnitude. They're just adding noise. And if they invent an alternative to string theory, they are <em>always</em> pure crackpotteries. There is no real alternative to string theory.<br /><br />At some moment, Sample was pushing the scientists to defend the thesis that gravitational wave detectors will be the experimental apparatuses that will test string theory. But none of them actually wanted to say that "the gravitational waves are the experimental silver bullet" for string theory by themselves. David said that it was just one among a huge number of rather far-fetched possibilities. The real point is that string theorists are working on strategies to advance knowledge that don't have the form of any simple-to-imagine experiment such as LIGO – strategies that are perfectly alright and contribute positive (and in almost no cases, negative) evidence that string theory works but strategies that intellectually limited people such as Sample simply cannot get. <br /><br />They cannot get it because they misunderstand even the simplest point that the judgement what is right and what is wrong in theoretical physics usually depends on refined proofs, calculations, and arguments that heavily depend on mathematical details. They have never witnessed an example of a mathematical argument that actually mattered – and that's why many of them assume it is impossible. They are only imagining that proofs may be of the form that the average mammals could understand as well. All their conclusions are intuitive. But the average man's intuition breaks down in high energy physics near the Planck scale. Well, it actually breaks down much earlier.<br /><br />The implicit assumption that string theorists are obliged to build some realistic experiments is just pure garbage. String theory has been a hardcore theorists' activity since the beginning. Also, from the beginning, it looked way more likely that the extra dimensions would be too small to be seen by doable experiments; for a while, larger extra dimensions were considered but even in that epoch, this possibility was considered far-fetched. There is nothing wrong about it. The claim that all physicists must be doing experiments is the Aryan Physics from Nazi Germany and it is complete nonsense.<br /><br />However, the numerous string vacua with several compactified dimensions have been proven to be <em>exactly as consistent</em> as the vacua with 10 or 11 large spacetime dimensions. The claim (repeated on the show) that string theory predicts a wrong number of dimensions is simply false, much like almost all statements about the science itself that Sample and the vanilla critic made in the discussion. No, we don't live in 3+1 dimensions if you count the dimensions carefully.<br /><br />Sample was also asking what the string is. Eleanor and David were attempting to tell him that string theory was just a name and instead, there's difficult mathematics he is unlikely to get. That's one important way to look – it is important because people should be explained that the arguments follow mathematics and not some intuitive opinions about the piano strings or something like that. Another way to look is that the string is a real 1-dimensional curve in space, an infinitely thin fundamental object. The positions and speeds of its points have to be treated as quantum variables etc. (and at stronger coupling, they cease to be uniquely fundamental) but it is fundamentally obtained from something like a real thin rubber band. Does Sample really need to ask that strings are really strings in 2019? String theory has been around for 51 years and for some 48 years, we've known that it was a theory that could be extracted from strings. Sample himself has discussed string theory many times. Is it really appropriate for a top U.K. newspaper to ask "what is a string"? And if a listener has no clue "what is a string", does it make sense for him to listen to much more complex questions about the status of string theory? Isn't it clear that such an incorporation of the listener is fraudulent? If someone doesn't even know "what a string is", not even in some laymen's caricatures of the answer, then he is very, very far from meaningfully thinking about the state-of-the-art questions of theoretical physics. The implicit claim that he can follow the arguments is clearly a lie.<br /><br />Also, we heard from Sample that string theory was more "controversial" than any theory in the history of science. Oh, really? And what about heliocentrism? Darwin's evolution theory? Relativity in Nazi Germany? Genetics in the Soviet Union? And indeed, quantum mechanics among the West's neo-Marxists of the recent 50 years? Important scientific theories often find people who oppose them. When the theories are correct, the people opposing them are pretty much idiots. That's the case of string theory's critics, too. The more idiots and the louder idiots you can find, the stronger the "controversy" will be. A theory's being "controversial" doesn't say anything whatsoever about the intrinsic properties of the theory itself. It says more about the critics. If you focus on some people's emotions and not scientific arguments themselves, then you are not doing science, you are not looking at the Universe in the scientific way, Mr Sample.<br /><br />Sample has also asked: How is it possible that the brilliant young people keep on starting to work on this theory, despite Sample's and vanilla critics' constant efforts to sling mud on string theory if not ban it? Isn't it because these young people <em>are brilliant</em>? While you are not? Brilliant people can figure that string theory is the state-of-the-art framework in which the most accurate theory of Nature must be studied as of 2019. They can figure out that the talk in the newspapers is just misleading or downright deceitful junk which is not addressed to them. People who aren't brilliant – and especially, people who are complete idiots – can't figure this out. They're effectively on par with the average monkeys – who are willing to absorb moronic slogans from vanilla critics. And that's why they get easily manipulated by the garbage in the Guardian and similar cesspools.<br /><br />But the average true monkey can usually understand that it is a monkey – different from the humans. The likes of Sample apparently can't get it. He seems incapable of even <em>inventing</em> the answer – or "possible answer", from his careful viewpoint – that the reason why brilliant people do string theory and he doesn't is that brilliant people can get it and the stupid people can't. He can't invent "create" the possible explanation of the young people's interest – namely that they are right and he is wrong. The fact that the smart people still say that string theory is correct looks like some giant conspiracy theory to him. He would clearly prefer an explanation involving the extraterrestrial aliens who keep the best theoretical physicists – young and older – hostage.<br /><br />Sample talks about career prospects etc. But he remains completely silent about – and it seems that he is totally failing to get or acknowledge – that "beautiful minds" are actually driven by their curiosity. They want to understand how the Universe works. It isn't about careers. A mediocre person like Sample isn't curious and isn't driven by any forces besides the animal instincts or his desire to make some money but he should be able to understand that some people simply are better and more "beautiful minds" than he is. These activists refuse to get it. Note that all the filthy anti-physics websites talk about the money all the time (how they can rob this group of physicists or another of some money) – and they don't care about the actual science. This clash is really both intellectual and ethical, string theorists are generally the good guys, and the anti-string individuals are the villains.<br /><br />Eleanor and David were effectively making the same points as I do but they made the statements in such a careful and polite form that they were unavoidably overlooked – and sometimes deliberately overlooked. I think that they sounded pleasant – but too pleasant, like some folks flying in the clouds who are disconnected from the Earth. With this attitude, while facing aggressive, ignorant, prejudiced bullies and chronic liars such as the vanilla critic, science becomes indefensible in the broader society. If scientists can't comprehensibly convey the point that critics of string theory are critics of string theory because they are low-IQ and/or dishonest biological waste or jealous because they can't be better, this point will just not get to the listeners, and it will be unavoidable for science to be increasingly treated like Galileo.<br /><br />David, you probably can't explain exotic branes in M-theory to too many Guardian listeners – although I do think that a healthy society would have radio stations that would try to explain exotic branes, too. But the sociological fact that various people who discuss these things belong to groups that differ by some 40 IQ points and by the equivalent of 5-10 years of intense study is something that you and others <em>should</em> be capable of communicating. What is at stake is the public's understanding of the very existence of science – and its basic preconditions such as the freedom of research without bullying, and hard work where some loudly pronounced demagogy isn't the ultimate weapon.<br /><br />It's questionable whether it's a good idea for scientists to help the journalists with creating content whose anti-scientific goal is determined at the very beginning. I think that Sample has decided what the "story behind the discussion should be" in advance – "string theory is controversial" – and nothing could change that plan because the likes of Sample don't care about the facts and arguments as they appear. Isn't a string theorist who helps this content to be produced a useful idiot unwillingly helping the ongoing campaign to delegitimize science? Isn't it wiser to acknowledge the reality – that lots of journalists are just very hostile towards science – and ignore or boycott these journalists?Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-55675369987464338442019-06-30T08:36:00.001+02:002019-06-30T09:15:03.936+02:00Higgs mass from entropy maximization?As you know, the Higgs boson is the most recently discovered fundamental particle (next Thursday, it will be 7 years from the discovery) and its mass seems to be \(m_H=125.14\pm 0.24\GeV\) or so. In various models, supersymmetric or scale-invariant or otherwise, there exist partial hints why the mass could be what it is and what this magnitude qualitatively means.<br /><br />Reader T.G. had to be blacklisted because he was too vigorous and repetitive in defending the highly provoking 2014 Brazilian paper<br /><blockquote><a href="https://arxiv.org/abs/1408.0827">Maximum Entropy Principle and the Higgs Boson Mass</a> (by Alves+Dias+DaSilva, about 12 citations now)<br /></blockquote>which claims to calculate the almost identical value \(125.04\pm 0.25\GeV\) using a new assumption, entropy maximization. What are they doing?<br /><br /><img src="https://twiki.cern.ch/twiki/pub/LHCPhysics/CrossSections/YRHXS_BR_fig1.png" width=407><br /><br />Look at this chart which they omitted, for unknown reasons, so this blog post is more comprehensible than the paper. <br /><br />The horizontal axis is the Higgs boson mass \(m_H\) and the vertical axis shows the branching ratios of Higgs decays – the probability that the Higgs decays to some final products or others. You may see that near the observed value \(m_H \sim 125\GeV\), there are relatively many decays that are relatively close to each other. None of them is dominant and beating all others etc.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />OK, the Brazilian folks simply postulated an obvious idea that you could have – what if Nature tries to maximize the diversity? OK, so they took the branching ratio as a function of the variable Higgs mass from some software on the market and maximized the Shannon entropy\[<br /><br />S = -\sum_{i=1}^m b_i (m_H)\ln b_i (m_H)<br /><br />\] where \(b_i\) are the branching ratios i.e. the probabilities of qualitatively different decays.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />What are the decays in the Standard Model? They are<br /><ul><li>\(\gamma\gamma\), \(W^\pm W^{\mp *}\), \(ZZ^*\), \(\gamma Z\)</li><li>\(e^+e^-\), \(\mu^+\mu^-\), \(\tau^+\tau^-\)</li><li>\(6\times q\bar q\)</li><li>\(g\bar g\)</li></ul>The asterisk indicates that one of the particles is virtual – which is the case if the real particles in the final state would be too heavy.<br /><br />OK, it's the three "particle-antiparticle" pairs of electroweak gauge bosons, the fourth similar but asymmetric decay is \(Z\gamma\), then there is the gluino pair, six quark pairs, and three charged lepton pairs. Now, the top quark is too heavy, heavier than the Higgs boson, so in the range of possible Higgs masses below the top quark mass, both tops would have to be virtual and the top-antitop Higgs decay is very unlikely.<br /><br />That means that instead of fourteen, they just consider \(m=13\) decays, calculate the entropy as a function of the Higgs mass, and claim that \(125\GeV\) is the value that maximizes the entropy – or the diversity, if you wish. Cute. The arguments in favor of this discovery are obvious:<br /><ul><li>they apparently obtained the right Higgs mass</li><li>they used something that seems rather canonical in the probability calculus, namely the <a href="https://en.wikipedia.org/wiki/Maximum_entropy_probability_distribution">maximum entropy probability distributions</a></li></ul>The latter tells you that if you know a probability distribution imperfectly, you should choose the distribution that maximizes the Shannon entropy \(-\sum_i p_i \ln p_i\). It's surely a special distribution in any restricted subclass, there is something canonical about it. However, the precise explanation "in what sense the Shannon-maximizing" distribution is "the best" is subtle and people may easily overstate its importance or unavoidability. In particular, I would say that if you obtain some probability distributions by proper Bayesian inference, you shouldn't replace it with a different one just because this different one maximizes the Shannon entropy. Instead, the prescription is only valid if you know the proability distribution "incompletely". But an incomplete distribution with "holes" etc. is something that you can't really get from measurements of the system if those are complete enough.<br /><br />Nevertheless, the maximum entropy distribution principle does recommend you to choose the "maximally ignorant", egalitarian-divided probabilities for the degrees of freedom that are unknown and whose uncertainty is unknown. OK, they maximize the function of the Higgs mass and claim that \(125\GeV\) is the sweetest spot.<br /><br />You may get overly excited by the positive arguments and neglect the doubts – suppress your skepticism. I think that in that case, you must be considered a numerologist. Like a broken clock, a numerologist may be right twice a day, of course. But the reasons to dismiss the result are really more powerful and fall into three categories:<br /><ul><li>errors and unnatural choices in the calculation even if you accept the fundamental premises</li><li>the apparent inability to calculate anything beyond the single number, the Higgs mass, using this apparently ambitious principle</li><li>the acausal character of the implicitly suggested "mechanism" which indicates that it should be impossible for such a maximization rule to operate in Nature</li></ul><b>Concerning the first class</b> of the complaints, I think it must be wrong that they consider just the 13-14 channels and the corresponding 13-14 terms in their entropy. Why? Because locally, the color of the quarks and gluons should be considered distinguishable.<br /><br />They were not calculating any "well-established kind of entropy in the context" or the "real entropy of any parficular physical system". They just took the Shannon entropy formula and substituted some numbers that look "marginally sensible" to be substituted. Because there's no meaningful underlying theory, I can't prove what is "right" and "wrong". Their formula is really their axiom, so it's "right" in their axiomatic system.<br /><br />But I find it extremely unnatural that there is no coefficient of \(3\) in front of their terms for the quark channels; and the corresponding factor of \(8\) for the gluon channel. For example, the gluon branching ratio should really be divided to 8 equal pieces \(b_{gg}/8\) and their logarithms additively differ by \(-\ln 8\). These extra terms \(\ln 8\) multiplying the gluon terms in their equation would modify the function \(S(m_H)\) and the maximization procedure.<br /><br /><b>Concerning the second class</b> of the complaints, their entropy maximization principle seems really cool. It is numerologically claimed to work for the Higgs boson. But if such a principle worked, wouldn't it be strange that it only works for the Higgs boson mass? The Higgs boson mass is just one parameter of the Standard Model. Shouldn't it work for the quark and lepton masses – or their Yukawa couplings – as well? Or the masses of the electroweak gauge bosons and/or the gauge couplings? Even if the principle only determined one parameter, shouldn't it be a more generic function of the Higgs mass and other parameters rather than the Higgs mass itself? Why the precise Higgs mass, a particular coordinate on the parameter space? And shouldn't such a principle ultimately determine even the constants that don't seem to be associated with decays such as the cosmological constant?<br /><br />You know, the claim – pretty much a claim that they try to hide – that such a procedure only determines the Higgs mass seems like a classic sign of a numerological fallacy. Numerologists love to take some number, completely take it out of the context, and produce some "calculation" of this number. They ignore that if some deep principle determines this number, the same principle should really determine <em>many other</em> numbers. The numerological derivations of a number have usually nothing to do with the "context", what the mathematical constant is actually supposed to represent. By definition, numerologists are too focused on patterns in numbers and largely ignore what the numbers are supposed to mean.<br /><br />They don't seem to discuss this problem at all which indicates either that they're deliberately obfuscating problems, which is dishonest, or they don't understand why this is a problem for almost all similar numerological determinations of any constants. In both cases, it's just bad. Aside from their overlooking of the color degeneracy factors, this is another reason to conclude that they're simply not careful physicists. And this conclusion makes it likely that they have also done some other errors, perhaps completely numerical ones, but (because my belief in the paper is close to zero) I totally lack the motivation to find the answer to the question whether such mistakes also plague the paper.<br /><br /><b>Concerning the third complaint</b>, well, such a maximization of entropy should be impossible for causal reasons. The higher diversity of the Higgs decays doesn't seem to "useful" to explain anything; there is no known carefully verified rational reason why it should be true. Unlike the extreme anthropic principle that favors "universes with many intelligent observers" because the intelligent observers are not only "like us" but useful for doing any science, and in this sense a desirable component of the universe, the diversity of the Higgs decays doesn't seem to be good for anything. So the justification is even more absent than in the case of the "strong anthropic principle" – and that is already pretty bad.<br /><br />The reason why this diversity should be a "cause" of the selection of the Higgs mass is lacking. Even more seriously, one may apparently prove that such a determination should be impossible. Why? Because the Higgs mass – and parameters resulting from some vacuum selection – took place when the Universe was extremely young, dense, and hot. Perhaps Planckian. And maybe even more extreme than that. At that time, Higgs bosons didn't have the low energy and didn't have the freedom to decay to something at low energies "almost in the vacuum". Everything had huge energy and was interacting with other particles – whose density was huge – constantly.<br /><br />So the "13-14 low-energy decay channels of a Higgs boson" weren't even an important part of the physics that governed the very early Universe when the vacuum selection choices were made! So how could the Universe make a choice that would maximize some entropy calculated from some low-energy phenomenological functions – which only seemed empirically relevant much later (but still a fraction of a second after the Big Bang)? It just doesn't make any sense. Such a mechanism could only work if the causal ordering were suppressed (which would almost unavoidably imply a conflict with the usual, causal laws of Nature that determine the evolution differently) and the universe were really planning the future in a teleological way. But why should exactly this kind of diversity be God's plan?<br /><br />Also, many superficial people who just defend some "entropy maximization" typically fail to understand that the right reasons and mechanisms for the entropy maximization in physics are known. They boil down to the second law of thermodynamics. The entropy goes up because the probabilities of a transition between the "initial ensemble of states" and the "final ensemble of states" is averaged over the initial states but summed over the final ones. That's why the probability of the inverse process is effectively suppressed by the factor of \(N_i/N_f\) which is why the evolution favors the evolution to higher-entropy states. This is the cleanest justification why the entropy doesn't want to go down.<br /><br />The second law of thermodynamics is a qualitative law but we actually know these quantitative proofs of this law and these derivations – similarly the H-theorem (the objection that it depends on "shaky" assumption such as the ergodic principle are bogus – all these assumptions are surely valid in practice) – tell us not only that the entropy goes up but also how much and why. If you postulate another "high entropy wanted" law for Nature, it may look like being a "morally allied" with the second law of thermodynamics. But because the details of your law – how high the entropy wants to be and why – will be different, your new law will actually contradict the well-established detailed derivations behind the second law!<br /><br />So the paper is hopeless.<br /><br />Nevertheless, over the years and even recently, I've spent dozens of hours by "spiritually similar" attempted derivations. In particular, those derivations were a part of my Hawking-Hartle research. The Hawking-Hartle state is the preferred wave function of the universe – especially applicable as the initial state of the universe – which is a solution of the Wheeler-DeWitt solution and may be obtained as a path integral in a spacetime region that isn't bounded by two boundaries (carrying the initial and final state), as appropriate for the calculation of the evolution or S-matrix, but just one boundary (a three-sphere surrounding the Big Bang point).<br /><br />The Hartle-Hawking state is clearly a possible paradigm to explain the parameters of Nature that won't go away unless another paradigm, like the multiverse, is really established – or some remarkable, rigorously provable bug is found in the Hartle-Hawking principle of the most general type. Or someone makes the Hartle-Hawking paradigm rigorous and quantitative and checks that it makes wrong predictions. But the Hartle-Hawking paradigm hasn't been terribly successful and naive, minisuperspace calculations of the Hartle-Hawking state dominate the literature.<br /><br />Well, I always wanted to apply it as a rule to determine the right vacuum of string/M-theory. All the numerous details about the compactified dimension could arise from the paradigm – while the non-stringy Hartle-Hawking literature is obviously too obsessed with the four large spacetime dimensions. If that's true, the Hartle-Hawking wave function could be peaked near the vacua with some qualitative properties. It could be peaked around vacua with a low cosmological constant or high Planck-electroweak hierarchies or high hierarchies in general or low Hodge numbers of the Calabi-Yau manifolds, among other "preferred traits".<br /><br />If the Hartle-Hawking paradigm is correct at all, and if string/M-theory is correct, which are two independent assumptions, then it seems extremely likely that the Hartle-Hawking state would prefer some qualitative traits of the string vacua. And they could be directly relevant for the explanation of some observed traits in Nature – such as the observation of some particular hierarchies or deserts.<br /><br />The Hartle-Hawking state would still allow many different vacua because it gives rise to a smooth probability distribution. But it could be peaked and the peak could be rather narrow near some point. The maximization needed to find such a point could be mathematically analogous to the Brazilian paper that I have discussed above.<br /><br />But the details matter. The Devil is in the details. And the details – which are not really small details, if you look at it rationally – imply that this Brazilian paper is hopelessly wrong and irrational. If someone is on a mission to promote it on the Internet and insult everybody who has good reasons not to take this Brazilian paper seriously at all, it's a problem and a ban becomes the optimal solution.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-78354743579067763932019-06-27T09:55:00.001+02:002019-06-27T15:49:30.720+02:00A three-parameter jungle of F-theory Standard Models<iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=B009YXFX0G&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>I want to mention two cool new papers now. First, a paper showing that natural supersymmetry is alive and well.<br /><blockquote><a href="https://arxiv.org/abs/1906.10706">The current status of fine-tuning in supersymmetry</a><br /></blockquote>Melissa, Sascha Baron-Cohen (Borat), and Roberto (Holland+Kazakhstan+Spain – and I've sent a few more people to arXiv.org again LOL) have analyzed the degree of fine-tuning in supersymmetric models using two widely accepted formulae. They found out that totally natural SUSY models are compatible with the LHC exclusion limits – the degree of fine-tuning is just 3-40 or 60-600 for low-scale measure or high-scale measure, respectively. <br /><br />The models get particularly viable if you look at the pMSSM (phenomenological minimal supersymmetric standard model – parameterized by a limited number of parameters close to the observations; I think it should have been expected) and the pMSSM-GUT is doing much better in fine-tuning than other GUT models. And when the fine-tuning depends primarily on the higgsino mass which may still be very low, and it's possible in huge regions of the parameter space, the fine-tuning may be very low.<br /><br />Tons of writers if I avoid the more accurate term "lying or deluded inkspillers" have persuaded some 97% of the Internet users who care – it's my estimate based on the comments I am receiving – that the LHC has excluded natural supersymmetry. Well, the calculations in the actual experts' papers show something very different. This 39-page-long paper with 9 MB of graphs concludes in the abstract: "We stress that it is too early to conclude on the fate of supersymmetry/MSSM, based only on the fine-tuning paradigm."<br /><br />So when someone tells you that the LHC has said something fatal about supersymmetry or naturalness, don't forget you are being lied to.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />That was on hep-ph. The second paper I want to mention is on hep-th and is dedicated to a similar topic as a <a href="https://motls.blogspot.com/2019/03/one-quadrillion-standard-models-in-f.html?m=1">quadrillion Standard Models in F-theory</a> in March:<br /><blockquote><a href="https://arxiv.org/abs/1906.11092">Generic construction of the Standard Model gauge group and matter representations in F-theory</a><br /></blockquote>Like Cvetič et al. in March, Wati Taylor and Andrew Turner (MIT) look for promising realistic classes of F-theory compactifications.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Taylor and Turner demand the final gauge group to be the exact Standard Model gauge group\[<br /><br />(SU(3)\times SU(2)\times U(1)) / \ZZ_6<br /><br />\] at all times. They like models with 6 uncompactified dimensions so they look at the F-theory models for those, assuming that the realistic 4D models are obtained as some compactification of two more dimensions from a 6D model that already has the correct gauge group.<br /><br />In six dimensions, one has to satisfy the nontrivial anomaly cancellation conditions. Note that in this 6D-to-4D F-theory model building, the 6D model is almost completely described by a geometry (an elliptically fibered 3-fold) and it mostly specifies the gauge group. While compactifying to 4D, one may and must add some fluxes (which are "non-geometric" information), and these fluxes are correlated with the chiral matter that appears in 4D physics.<br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=0821893963&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>They impressively claim that if they assume the right gauge group above; the MSSM matter spectrum; six large dimensions; and the absence of tensor multiplets in 6D, they have a complete proof of having found <em>all</em> F-theory compactifications with these conditions. Somewhat less certainly, they want us to believe that even if the "no tensor multiplets" condition were relaxed, or if 6D were replaced by 4D, they could still do a similar classification.<br /><br />A cool result is that the largest bunch of constructions obeying these conditions is a well-defined class of compactifications that are obtained by Higgsing \(SU(4)\times SU(3)\times SU(2)\) F-theory models in 6D. This class is parameterized by 3 parameters: \(b_3,b_2,\beta\). 71 such models exist when there are no tensor multiplets. Three bifundamental fields are involved in these vacua, various bases are possible.<br /><br />You know, the three parameters are just integers and they have to obey inequalities\[<br /><br />\eq{<br />4b_3 + 3b_2 + 2\beta&\leq -8a\\<br />b_3+b_2+\beta &\geq -a<br />}<br /><br />\] These inequalities bind the integers from both sides and there are 98 solutions. Geometries may be built for each etc. although I feel they only superficially mention the geometries – and their Fano bases and other bases etc. The paper is more field-theoretical than geometric in character.<br /><br />It seems that the authors must really love the \(SU(4)\times SU(3)\times SU(2)\) in 6D and trust it's a promising extension of the existing groups. It's not a Pati-Salam group – they also have some Pati-Salam realizations of the Standard Model – but this Taylor-Turner seems to be analogous to Pati-Salam and according to this analysis, it may be favored over Pati-Salam in F-theory.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-1970826501184437922019-06-26T18:47:00.000+02:002019-06-30T06:08:53.408+02:00Are feeling-based popular articles about symmetries helpful?<a href="https://motls.blogspot.com/search?q=K+C+Cole&m=1&by-date=true">K.C. Cole</a> is one of the better science writers – who is surely choosing better sources for her texts than almost all other writers about physics – and she just published a new text in the Quanta Magazine:<br /><blockquote><a href="https://www.quantamagazine.org/einstein-symmetry-and-the-future-of-physics-20190626/">The Simple Idea Behind Einstein’s Greatest Discoveries</a><br /></blockquote>The title is friendly towards symmetries, as you can see, and many parts of her text try to suggest details about the importance of symmetry in the 20th and 21st century physics. The subtitle is unfriendly, however:<br /><blockquote>Lurking behind Einstein’s theory of gravity and our modern understanding of particle physics is the deceptively simple idea of symmetry. But physicists are beginning to question whether focusing on symmetry is still as productive as it once was.<br /></blockquote>I concluded that the real intended story is that the symmetries are no longer considered as fundamental as they used to be. And I think that such a statement would be correct – although this transition wasn't really taking place in 2019 but rather in the 1990s or 1980s. However, I don't think that the body of Cole's article actually contains evidence that a rational reader could consider a justification of her subtitle.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />OK, her article touches many topics related to symmetries: special relativity and the Lorentz invariance, beauty of equations according to Dirac, general relativity and its vaguely suggested connection with symmetries, Emmy Noether, global symmetries vs gauge symmetries, gauge symmetries' being redundancies, spontaneously broken symmetry as a non-symmetry of solutions when the equations are symmetric, and many other topics. <br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />But each of these topics is sketched or mentioned so superficially (and she jumps from one topic to another so quickly) that I find it inconceivable that someone could actually <em>understand</em> any of these insights, even partially, after having read the article. To be more precise, I haven't been persuaded that the writer actually understands any of these things herself. Like how the Lorentz symmetry acts in special relativity. Or what the spontaneous symmetry breaking does in physics. <br /><br />Or what Emmy Noether is actually famous for. Cole seems to promote partly wrong statements, such as that Noether has linked the energy conservation in GR to the symmetry exchanging reference frames. Well, the relevant symmetry transformation related to the energy conservation law is a time translation, not really something that we consider "switching between reference frames". On top of that, these coordinate-changing symmetries are just redundancies (local symmetries) in GR, so there's <a href="https://motls.blogspot.com/2010/08/why-and-how-energy-is-not-conserved-in.html?m=1">no general [total] energy conservation law in generic spacetimes of GR</a>! So the sentence seems to be defective at so many levels that I concluded that it can't be a bunch of coincidences. The writer must really fail to understand how it works.<br /><br />Despite this big uncertainty about the understanding of <em>anything</em> by the writer, the writer nevertheless feels confident enough to present the far-reaching conclusions such as "the symmetry isn't as productive as it used to be". Is that statement right, a rational reader must ask? Can the communication of such feelings – and they're really feelings, not conclusions of any rational analysis – be helpful to direct readers' searching for his own understanding? I just doubt it.<br /><br />Does it make sense for a youngster interested in physics to read articles about symmetry that are written by someone who doesn't actually understand any of the stuff at a level recognizable to the experts? My answer is No.<br /><br />In the past, good popular writing about science <em>was</em> sort of analogous to textbooks that actually try to train someone so that he really understands the stuff and may become a professional. Popular books – e.g. Martin Gardner's books about relativity – were more playful, slower, using some stories, but the basic goal was the same as the goal of the textbooks.<br /><br />I think it is no longer the case. Articles such as Cole's don't actually want to teach anything to anybody and they can't even persuade the experts that the writer actually understands what she is writing about. Articles such as Cole's are communicating some feelings and some predetermined, intrinsically political conclusions that the readers are expected to parrot. The reader should simply take it as a fact – because it's written by a person widely called a "science writer" – that symmetry used to be very productive but it is no longer the case. It's too bad because it has very little to do with science and the scientific method of changing collective or individual opinions about <em>anything</em>. The word "science" is just being stolen for something that is no longer "science".<br /><br />OK, where are the places of the body that show that practitioners no longer consider symmetry productive? Here is the first one, I think:<br /><blockquote>There has been, in particle physics, this prejudice that symmetry is at the root of our description of nature.<br /></blockquote>Right. I would agree with Justin Khoury. It's been a pillar of some faith, some armchair physicists still look at the things in this way, and real experts generally believe that this complete obsession with symmetries is wrong today. And Khoury has used a relatively hostile word "prejudice" for what used to be the status quo.<br /><br />Well, it may have been a prejudice. But you could also call it a "lore". I think that Khoury wouldn't protest if the word "lore" had been used instead of "prejudice". It doesn't really make any difference for a physicist – but for journalists like K.C. Cole who are obsessed with feelings, the difference between "prejudice" and "lore" could be substantial. The special relativity is built from the Poincaré symmetry, GR is built from the diffeomorphism symmetry, the Standard Model may be built from the \(SU(3)\times SU(2)\times U(1)\) gauge symmetry, and so on. That was a picture of the past – a reason why physicists tended to consider the symmetry primary.<br /><br />We no longer see it in this way – because symmetries may be emergent, accidental, flexible, appearing, disappearing, and gauge symmetries aren't real physical symmetries because they're redundancies that depend on the chosen description of physics – but Cole hasn't really explained why. She doesn't really explain why the gauge symmetry is just a redundancy. She doesn't explain how the descriptions with different gauge symmetries may be dual to each other, how they may be gauge-fixed or deformed to each other on the moduli space, and so on. So the reader is just expected to <em>mindlessly copy</em>, without any real evidence, the opinion of K.C. Cole that "symmetry is no longer as productive as it used to be" although there is no real justification of that assertion in the article. If we don't count some negatively sounding words without sentences, such as "prejudice" in someone's quote, and indeed, we shouldn't pay attention to those.<br /><br />That's bad. Whether the reader understands one thing or another about symmetry has some limited importance but there is something more important at stake. For a reader to be scientifically literate, he just shouldn't accept assertions that aren't justified by any evidence. This kind of "skepticism" or "caution" is an essential prerequisite for the scientific thinking about anything. And this article is an example where the principle fails. If the reader behaves rationally, the article won't really move him by a micron. It's a useless article. A necessary condition for the article to actually move someone's ideas somewhere is that he <em>blindly believes what he reads</em>. And that's a deviation from the scientific discourse that is much more devastating than a misunderstanding of one technicality involving the notion of symmetry or another.<br /><br />Well, there are two more segments in the article that could be claimed to be "the evidence that the importance of symmetry has dropped":<br /><blockquote>Over the past several decades, some physicists have begun to question whether focusing on symmetry is still as productive as it used to be. New particles predicted by theories based on symmetries haven’t appeared in experiments as hoped, and the Higgs boson that was detected was far too light to fit into any known symmetrical scheme. Symmetry hasn’t yet helped to explain why gravity is so weak, why the vacuum energy is so small, or why dark matter remains transparent.<br /><br />[...]<br /><br />At the same time, symmetry-based reasoning predicted a slew of things that haven’t shown up in any experiments, including the “supersymmetric” particles that could have served as the cosmos’s missing dark matter and explained why gravity is so weak compared to electromagnetism and all the other forces.<br /></blockquote>The only problem is that these assertions are mostly wrong. The new particles haven't shown up in experiments <em>so far</em> and there has never been any universally enough accepted prediction of a whole framework – as opposed to particular competing models that make lots of assumptions – that some new particles should have shown up by now. All the predictions assuming naturalness are <em>probabilistic</em> predictions that have never guaranteed and could never guarantee the discovery of anything. Supersymmetric particles remain the most well-motivated possible particles in new physics.<br /><br />Nothing has qualitatively changed. It has always been known that supersymmetry and perhaps other symmetries relating the Higgs boson to something else etc. have to be broken. And all these qualitative things remain true and promising possibilities. In particular, it's comparably likely to the probability of the 1990s that the weakness of gravity or the smallness of the cosmological constant has an explanation in which symmetries play an important role. The lightness or stability of the dark matter probably depends on some new symmetry, too. These possibilities have not been <em>ruled out or falsified</em>, at least not if one uses the scientific definitions of these verbs.<br /><br />Symmetries still play many roles in all of that – and they unavoidably appear in newly proposed explanations of observations in physics. Supersymmetry is a symmetry, or a Grassmannian generalization of Lie algebras. Also, symmetries surely do explain why dark matter is transparent, whatever it is. Dark matter is dark because it doesn't interact with the electromagnetic field and it doesn't interact with the electromagnetic field because its pieces are electrically neutral – i.e. invariant under the electromagnetic \(U(1)\) symmetry transformations! K.C. Cole is basically saying that the notion of symmetry is being <em>expelled</em> from the reasoning about all these questions but it's obviously complete nonsense. It will never be expelled because these are settled connections and explanations and the symmetry will never lose its role in those explanations. The only thing that is happening is that there may be a <em>deeper</em> explanation of these known things where the symmetries aren't among the most fundamental concepts.<br /><br />The statement that "symmetries don't explain why dark matter is transparent" is either wrong or vacuous and no real expert would make such a statement. (I just picked an example but the same criticism applies to many other propositions in Cole's article.) But in the genre such as K.C. Cole's article, it's just fine to write such wrong statements because the <em>political spirit</em> is consistent with the main message she wants to convey. She wants to convey the view that <em>symmetry has deteriorated in recent years or decades</em> – which is really a feeling, not a fact – and she thinks that given this goal, anything "negative" may be or should be written about symmetries. Whether the statements are actually correct doesn't have to be verified. <br /><br />So she isn't really teaching any physics – the primary reason is that she probably doesn't understand any. But even if I remain slightly uncertain about this proposition, there are just way too many hints in the article that it's a material written by and for "humanities" types, for people interested in feelings, grievances, entitlements, and identity politics, not for the "natural science" types who care about equations, experiments, mathematical proofs, and facts.<br /><br />What are the signs that this belongs to the "humanities" genre? One of the traits that are innocent but they drive me up the wall is the permanent attribution of some elementary statements to physicists. So she has communicated with five main physicists: Stephon Alexander, Robbert Dijkgraaf, Mark Trodden, Justin Khoury, and David Kaiser (a part-time historian). Sorry if I overlooked someone.<br /><br />In her article, you find 4 quotes of the type "Alexander said this or that". "Trodden said this or that" about 5 times, "Dijkgraaf said this or that" 4 times, "Khoury said something" 3 times, and "Kaiser said something" 6 times. That's 22 similar quotes in total. You know, people may have different <em>opinions</em> but most of science just isn't about some idiosyncratic opinions. Physics is an objective natural science. And most of the stuff she talks about really <em>is</em> some physics that has been settled for 50 years – and in very many cases, over 100 years.<br /><br />Most of the 22 quotes end up being similar to<br /><blockquote>“If that weren’t the case [the Cosmos is uniform at cosmological scales, a manifestation of a symmetry], cosmology would be a big mess,” Khoury said.<br /></blockquote>Do you understand why I am angry about that? It just doesn't matter at all that it was Khoury who said it. Every competent cosmologist could say – and has said – a sentence that is nearly equivalent. If the Universe were inhomogeneous at the cosmological scales, we couldn't design neat FRW Ansätze for the cosmological evolution and we would have to study "where we exactly live" because the phenomena we observe around the Solar System would heavily depend on our special place in the Universe. Are we close to some "center of the Universe" or far from it? Those things would matter. But there's no real "center of the real Universe" where we live so cosmology may avoid these questions and the research of cosmology is cleaner. We may study the whole Universe by observations made from the Earth and we may extrapolate most of the conclusions to the whole Universe, too. Thank God.<br /><br />Khoury knows it. But I assure you that Dijkgraaf, Alexander, Trodden, your humble correspondent, maybe Kaiser, and everyone else who got a well-deserved good grade in a cosmology graduate course knows these things, too. The first problem with the attribution is that lots of laymen who read Cole's article will conclude e.g. that Justin Khoury is the guy who discovered that the Universe was uniform, or that the uniformity was important, or that it was related to symmetries. Just to be sure, he didn't discover either. To make things worse, I haven't even been persuaded that Cole herself understands that Khoury didn't discover either!<br /><br />But there's a more general problem resulting from the attribution. It's about the spirit of science.<br /><br />You know, technically, it may be right that Khoury said this or that, Trodden said this or that, Dijkgraaf said this or that, and Alexander said this or that. But by making these assertions that are attributed to somebody, K.C. Cole implicitly also says something else, namely that it <em>matters</em> who said it. But this implicit assertion is completely incorrect. In science, it doesn't matter who made one proposition or another. In physics, <em>black lives don't matter</em> and white lives don't matter, either. Also, men don't matter. Let alone women. Natural science isn't about humans or personal opinions. It's about objective evidence that is accessible to <em>everybody</em> with a sufficient intelligence, integrity, attention, background, and patience. It's just not true that everything is personal. The number of correct theories of relativity or the correct interpretations of quantum mechanics is fewer than 26, the number of genders. The only thing that is equal to the number of genders is the spacetime dimension of bosonic string theory. ;-) Even the number of genders is really lower than those people assume but I don't want to make my text controversial by suggesting that there exist men and women! ;-)<br /><br />So she doesn't really explain any of the points about the importance of symmetries – or the decline of that importance – at least not quite correctly. But she does explain something that surely affects many readers. And the influence is harmful. She conveys the totally wrong lesson that it matters who made a proposition in physics. She is helping to brainwash the readers into thinking – or failing to think – in analogy with the brain-insufficient practitioners of the humanities. People who want to mindlessly parrot and who are just choosing their allies in an <em>ad hominem</em> way, to share the grievances with them. People who don't give a damn about evidence, logical arguments, equations, or observations. At most, they <em>say</em> that they care about the evidence etc., because it "sounds nice", but they're lying because in practice, they are using something completely different to decide what they should root for etc.<br /><br />That's why I think that the net effect of articles such as this K.C. Cole's text is <em>negative</em> and because K.C. Cole's article is still one of the <em>best</em> popular texts about physics that are appearing in (almost) mass media these days, it seems obvious that the net contribution of the science writers as an occupation to mankind's scientific literacy is <em>unquestionably negative</em>. They're really helping mankind to evolve towards Idiocracy. Maybe some other journalists are even more harmful but that doesn't imply that the current science journalists have a positive sign.<br /><br />You might suggest that there's a simple "legitimate" explanation why she attributes mostly elementary statements to the 5 physicists 22 times. She isn't a real authority. So it's right for her to "report what the authorities say" which is why the statements are more authoritative once the physicists endorsing them are named. But if that's so, I would like to know the name of the physicist who has recommended the far-reaching and controversial summary in the subtitle, or any of the wrong statements such as "symmetry hasn't helped to explain why dark matter is transparent". It seems she is making the text look more authoritative by attributing some (sensible) statements to physicists, but the most important statements are wrong, unattributed, and the reader is supposed to overlook it.<br /><br />This mess is unavoidable in the "humanities" type of science journalism. You know, if one writes good popular science, one doesn't need to refer to the authorities. It's just good, the smart readers see it, and some experts who read the popular stuff will see it, too. Martin Gardner – to continue with an example I mentioned above – was primarily keen on recreational mathematics. He was no professional physics researcher, ever. But he just understood special relativity well. He wrote popular books about it where he didn't need to refer to "authoritative" sources because the real authority came from the arguments that made sense because he actually understood the stuff. <br /><br />These days, journalists and popular writers generally understand nothing and their writing doesn't make much sense beyond the universal templates that they have learned in their journalism courses which is why they have to build on obnoxious appeals to authorities and why their texts unavoidably end up being misleading political tirades. Many of them openly disagree with the thesis that science is about the evidence, about the arguments' making sense, not about authorities (many people claiming to be science journalists are even willing to support insane clichés about the formidable 97% consensus and similar things). That's a simple way to see that the ideas and especially the methodologies they are trying to spread have very little to do with science. They're mostly abusing the word because it has earned quite some capital and they find it useful to be parasites on the good name of science. But the capital wasn't earned by these journalists or their type of "work" at all.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-72425676004470680472019-06-24T08:26:00.000+02:002019-06-24T17:20:08.397+02:00Turok et al.: a quantum fluctuation complaint against inflation<b>...and like most of Turok's papers, it's fundamentally wrong...</b><br /><br />Most of the arXiv.org papers that I cover are papers that I consider good – innovative, interesting, correct, solving something, presenting real possibilities. But I am not one of those people who think that people's judgement should be censored so that only "nice" appraisals are heard. In a healthy scientific process, one must unavoidably hear about wrong and bad papers. The elimination of wrong things is actually the <em>primary</em> procedure that the scientific method revolves around.<br /><br />One very bad hep-th paper today is<br /><blockquote><a href="https://arxiv.org/abs/1906.09007">Quantum Incompleteness of Inflation</a><br /></blockquote>by Di Tucci, Feldbrugge, Lehners, and Turok (Potsdam+Perimeter). Helpfully enough, the alphabetic sorting of the author names coincides with the sorting according to the increasing age or experience. Neil Turok is obviously the "boss". The last, oldest three authors have written numerous <a href="https://motls.blogspot.com/search?q=Turok+Hartle+Hawking&m=1&by-date=true">wrong papers criticizing the Hartle-Hawking paradigm</a> for the initial wave function of the Universe. Now, Alice Di Tucci, the most junior member, was added to write a very similar criticism of cosmic inflation, too.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Neil Turok has written numerous papers claiming that inflation and other pillars of state-of-the-art physics is just wrong. He has claimed that inflation didn't solve any problem of the fine-tuning style. I believe that his criticisms unmask his deep misunderstanding of the difference between the past and the future, the fundamental rules of reasoning in science, and he generally fails to get what a good student must understand rather early on.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />As I discussed e.g. in <a href="https://motls.blogspot.com/2014/03/alan-guth-and-inflation.html?m=1">Alan Guth and Inflation</a>, one may easily explain why cosmic inflation solves the flatness problem and other problems. By assuming such an innocent thing as a positive value of the vacuum energy density \(V(\phi)\) as a function of a scalar field, the inflaton, it produces a de Sitter space which may be sliced in an FRW way. In those coordinates, it looks like an exponentially expanding space. The volume naturally goes up and the density of magnetic monopoles, perturbations of the metric and other fields etc. goes down. So one naturally produces a nearly perfect exponentially large space with exponentially small defects and perturbations. It still has a lot of energy density in the inflaton's kinetic energy and that may be used to create nicely homogeneous seeds of galaxies at the end of the inflation.<br /><br />The flatness may be described by the parameter \(|\Omega-1|\), a deviation from the flatness. In the normal cosmology, one may show that as the Universe was getting older, \(|\Omega-1|\) was visibly increasing. Because \(|\Omega-1|\) is observed to be really small even today, the regular cosmology implies that it had to be <em>really tiny</em> when the Universe was really young. Because this unnaturally small value of \(|\Omega-1|\) had to be chosen in each region of the Universe which seems independent from all others, the required amount of fine-tuning seems insanely huge. Inflation modifies this conclusion by a term from the vacuum energy density that basically implies that \(|\Omega-1|\) has been going down, so its small current value is <em>explained</em> assuming natural enough initial conditions. Within inflation, the large, nearly flat, nearly homogeneous, nearly monopole-free etc. Universe is a largely unavoidable result of some evolution that only differs from the regular inflation by some de-Sitter-related terms with the opposite sign than we're used to.<br /><br />The explanation involving the exponential expansion is analogous to an explanation of the destroyed Hiroshima in Summer 1945. That event has boiled down to a nuclear chain reaction – another exponentially growing process. The existence of an object – the Little Boy – which is qualitatively similar to other objects (because uranium is analogous to hydrogen) but that also naturally ignites a chain reaction is an explanation of a huge explosion. In the same way, inflation is an explanation of the explosion that has made our Universe this large and nearly flat etc.<br /><br />Turok just doesn't get that the equations of inflation make the "final state" which we observe much more plausible – not insanely unlikely – and he nonsensically talks about the highly special fine-tuning of the initial conditions which the inflation demands – which is clearly the opposite of the truth.<br /><br />Lots of cosmologists have explained to him why he is just plain wrong but he keeps on pretending that he still believes in his bogus criticism. Now, "on top of his usual powerful arguments against inflation", as he spins them, he also adds a "quantum mechanical criticism". It seems very clear to me that Turok has first decided what the conclusion should be and then he ordered the three more junior collaborators to write some equations – almost 100 displayed equations, rather non-trivial ones – to make the paper look more scientific. But the equations don't actually imply the conclusions when you're analyzing things properly.<br /><br />What is the basic logic supposed to be? They calculate something about the inflation using the Picard-Lefschetz theory, the same mathematical method that Turok has employed in his <a href="https://motls.blogspot.com/2019/06/most-laymen-have-remarkable.html?m=1">criticisms</a> of the Hartle-Hawking program. In something they call the semiclassical approximation, although it differs from all the calculations that are considered the semiclassical approximation by sane cosmologists, they decide that the path integral gets contributions from two stationary points, not just one. Aside from the expanding Universe, there is also a history involving a bounce. Here a miracle occurs, they suddenly claim that it means an inconsistency, and inflation is doomed.<br /><br />None of these big statements make any sense. If they analyzed the perturbations using the semiclassical methods properly, they would find out the usual conclusions about the spectrum of primordial gravitational waves that are predicted by cosmic inflation – and related things. Instead, they just use all these terms and their equations as tools to make their wrong statement – the inflation doesn't work – look more credible.<br /><br />It makes no sense to go through all the equations and I am convinced that not a single reader of their paper aside from themselves will pay attention to every equation in their paper. What's more important is that the big methodological assumptions how all the mathematics should be used are incorrect. For example, on Page 11, we read<br /><blockquote>The propagator consists of the interference of two classical solutions. <br /></blockquote>But this sentence is a deep misunderstanding of the perturbative treatment of a QFT. A propagator is by definition the building block that is extracted from the quadratic approximation of the action as it fluctuates around a <em>single</em> classical configuration. If you derive Feynman diagrams – with propagators and vertices – you must first find a classical solution, i.e. an extremum of the action, then you expand the action around that point. The terms linear in the perturbations are absent because it is a solution. The bilinear ones give you a free field theory and you derive the propagators from them. And the higher-order ones produce the vertices.<br /><br />To write a propagator as a sum over two different classical solutions is just a conceptual mistake.<br /><br />OK, they discuss the existence of two saddle points as if it were a catastrophe. It's normal for basically any nontrivial function of a complex variable to have two or many saddle points. This mundane fact doesn't imply any breakdown of mathematics or physics which is what they irrationally claim. One must be careful how to treat the several points. In most cases, it's just one of them that is dominant and the others contribute some tiny corrections or great corrections to very special effects that would be otherwise impossible (e.g. 't Hooft's interaction coming from instantons) or something else. <br /><br />The existence of additional stationary points is interesting physics to be studied, not a sign of the Armageddon!<br /><br />The propagator obtained from two stationary points at the same time isn't the only conceptual blunder in the paper, of course. For example, on page 32, we read:<br /><blockquote>Our calculation demonstrates that quantum gravity effects cannot be ignored at the beginning of inflation – put differently, the beginning of inflation is highly sensitive to UV effects, not just in the sense of its potential being sensitive to curvature corrections etc., but also in terms of its quantum vacuum. Since all predictions of inflation depend sensitively on the quantum vacuum, this is not a small issue.<br /></blockquote>These sentences clearly show that they just don't get what is the "range of validity" of inflation or "what interval of issues inflation is supposed to address". The beginning of any theory about the very early events in the Universe is <em>unavoidably</em> sensitive to UV effects because the Universe started as a small and hot one which is where the UV effects matter. In principle, at the very beginning of the life of the Universe, the finest effects in quantum gravity or the Planck scale physics matter. This is not "bad news" in any way. It's basically a tautology – two nearly equivalent ways to describe the very <em>scientific discipline</em>. To spin this fact negatively is totally irrational.<br /><br /><iframe width="560" height="315" src="https://www.youtube.com/embed/Sj_9CiNkkn4" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe><br /><br /><em>An ABBA song about Turok's town and the victory status of his papers.</em><br /><br />But cosmic inflation isn't a final theory of quantum gravity solving all the subtleties of the Planck scale physics. Instead, cosmic inflation is another epoch in the history of the Universe which took place at shorter characteristic distances (and higher energy scales; and when the Universe was younger) than the regular big bang theory; but the scale of inflation is still assumed to be lower than the Planck scale.<br /><br />However, the beginning of inflation is close enough to the Planck scale which means that all relevant physical questions of that moment are obviously sensitive to the UV physics to a greater extent than the low-energy phenomena that e.g. condensed matter physicists observe today. But the success of inflation is that <em>the end of the inflation</em> is almost insensitive to the detailed initial conditions. The fundamental dumbness of the Turok-style criticism of inflation is that he always talks about the "beginning" where the alleged Turok problems are supposed to hide.<br /><br />But that completely misses the point because what inflation – or a similar cosmological theory – explains or is supposed to explain isn't the beginning of inflation but the <em>end of inflation</em> or the <em>current state of the Universe</em> which is what we actually observe! Because the regular big bang theory epochs seem to be theoretically understood, at least approximately, the understanding of the "present state of the Universe" is almost equivalent to the understanding of the "end of inflation" – one may rather reliably translate between these two moments. You can't find any comment about the "end of inflation" in his papers!<br /><br />If there are some Planckian pathological effects that seem wrong in inflation, it's at most a challenge, not an argument against inflation. Unless Turok or someone else performs a rigorous analysis of inflation within a consistent theory of quantum gravity, which probably means string theory, and they haven't done so, any analysis must be considered preliminary and any inconsistency in it may very well be an illusion. Even if the success of inflation were "only" confirmed at the classical level, it would be huge evidence in favor of inflation – and a reason to try harder.<br /><br />The success of inflation is that as inflation proceeds, and adds some 50-60 or more <em>e</em>-foldings to the size of the Universe, the conditions in the Universe get more hospitable and more compatible with our observations at the present which is a <em>good thing</em>. That's how scientific theories are supposed to work: they add some mechanism or something that should explain our <em>present</em> observations. The scientific theories are rated according to how well they perform <em>this task</em>. The focus by Turok et al. on the beginning of inflation or its assumptions means that Turok et al. don't really understand the scientific method as a whole. Science can't dismiss a theory <em>a priori</em> (incidentally, they spell it as "a priory", oops). Science evaluates theories according to their ability to produce lots of desirable conclusions about the present observations from a limited set of assumptions (e.g. about the initial state).<br /><br />The new Turok et al. paper has lots of pictures, with some contours in a complex plane. The prettiest picture is the colorful one on page <a href="https://arxiv.org/pdf/1906.09007.pdf#page=22">21 (22 of 37)</a>. You may see that the content of this colorful picture is very similar to the pictures in <a href="https://arxiv.org/pdf/hep-th/0301173.pdf">my 2003 paper</a> with <a href="http://inspirehep.net/search?ln=en&ln=en&p=find+a+motl+and+a+neitzke+and+title+hole&of=hb&action_search=Search&sf=&so=d&rm=&rg=25&sc=0">Andy Neitzke</a> (which is approaching 250 followups). In fact, the contexts are really analogous – perturbations in a gravitational theory – and we were dealing with some highly analogous problems (I won't say that the problems are completely equivalent but the proximity is clear).<br /><br />In my and Neitzke's calculation of the quasinormal modes – a new method, after a "<a href="http://inspirehep.net/search?ln=en&ln=en&p=find+a+motl+and+title+analytical&of=hb&action_search=Search&sf=&so=d&rm=&rg=25&sc=0">continued fraction</a>" algebraic method that cracked the problem a month earlier – we dealt with some Bessel's functions and two independent solutions of a related equation, an "outgoing wave" and an "incoming wave". In the complex plane, these two were mixing up with each other according to some monodromy rules. We needed some 3 weeks of intense thinking to clearly formulate what is happening with these two solutions and how the effects – and the monodromy – implies the statement about the frequency that was proportional to \(\log 3\), as we knew in advance.<br /><br />So we knew the right result, we knew that a "monodromy" was relevant from the beginning, but we were still confused about detailed properties of the statement we wanted to make that would imply what we needed. But we would have never published a paper before it made sense – e.g. a paper claiming that the \(\log 3\) isn't there because we couldn't prove it for 3 weeks, or a paper claiming that the quasinormal modes calculations are intrinsically inconsistent or something like that. If things don't make complete sense after 2 weeks, well, you need at least 3 weeks! A blurry, confusing picture that someone preserves for some time proves <em>absolutely nothing</em> – except for an upper bound on the professional skills of the person. Here, Turok et al. are also dealing with the co-existence of two solutions describing some perturbations of a metric in general relativity. And they also just try to fill details to obtain a result they "know", namely that there is something wrong about inflation.<br /><br />The main difference is that the result we assumed with Andy as a known one was correct because it was actually calculated by another solid method of mine (also approaching 250 citations). On the other hand, Turok is only trying to defend an arbitrary, wrong, unjustified or unjustifiable assertion against inflation. If he thinks that it's supported by something, it's mainly supported by his ego that outshines his physics abilities by several orders of magnitude.<br /><br />It's unfortunate when research is organized in this way – when senior collaborators who have mostly produced wrong statements in their life get the power to "force" their junior collaborator to collaborate on the technical content of a paper whose conclusion is both incorrect and decided in advance. Such junior collaborators are turned into <em>collaborationists</em>.<br /><br />This paper is just wrong. Aside from the misunderstanding of "what it means for a theory to explain something" and some rudimentary conceptual mistakes, what I find amazing is how the authors completely ignore what is actually known about these matters. People have used equivalent semiclassical calculations to calculate the primordial gravitational waves predicted by inflation and related effects. One could argue that the knowledge of these calculations belongs to the required toolkit of any modern theoretical cosmologist today. Turok et al. don't say what's wrong with <em>those</em> calculations. They just present their, different calculation whose final claims are completely different and clearly much less compatible with the observations. Nevertheless, they seem to suggest that this new, very different calculation should just replace the normal semiclassical claculations of inflation because Turok has a larger ego. Sorry, science doesn't work in this way.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-29243157526961681142019-06-21T08:24:00.000+02:002019-06-21T08:35:38.841+02:00McAllister et al.: weak gravity makes some low-volume cycles mandatoryOut of the 14 new <a href="https://arxiv.org/list/hep-th/new">primarily hep-th papers</a> today, about 8 (a majority) may be counted as "string theory" which is great. Even more impressively, 4 papers are about Calabi-Yau manifolds. Let me look at the first one – which was posted at 18:00:00 UTC, guaranteeing the first place. These guys may have mastered the correct calculation of the delay after you press the enter key and after the packets get to the arXiv.<br /><br /><span class="noborimg"><img src="https://lh3.ggpht.com/lubos.motl/SNzHOSzB_JI/AAAAAAAABCo/hQHOSzwUfcY/animated-quartic.gif" width=407></span><br /><br />A counting problem involving the Calabi-Yau manifolds is one of the most popular examples of the deep implications that string theory has for the world of mathematics. <br /><br />A real-six-dimensional manifold of a particular topology, the quintic (or the quintic hypersurface), has some non-contractible lower-dimensional manifolds in it. Some of them are (complex) "lines" in some algebraic sense. Their number has been known to be 2875 for quite some time. The more complex submanifolds, the "conics", are more numerous. Mathematicians have only known that their number was 609,250 since 1986.<br /><br />To count the higher-degree curves seemed like an impossibly difficult problem for the mathematicians. Suddenly, string theorists arrived and claimed that the Calabi-Yau manifold above was a mirror dual to another – string theory on both manifolds may be exactly physically equivalent – and physicists were therefore able to easily compute as many numbers in the sequence as they wanted, thus proving that string theorists are better mathematicians than the mathematicians.<br /><br />As all TRF readers surely know by heart, the next two entries are <a href="https://en.wikipedia.org/wiki/Quintic_threefold">317206375 and 242467530000</a>.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Mirror symmetry is surely deep in this sense. I've been uncertain whether the Weak Gravity Conjecture is comparably deep. It's just some lame and seemingly obvious claim about the strength of the forces, right? Well, Kevin McAllister and his family (Cornell+Northeastern – but ancestrally, Stanford's settlements on the East Coast) elaborated on a clever way to show that the Weak Gravity Conjecture has deep implications for geometry which are somewhat analogous to the counting problem for the Calabi-Yau manifolds:<br /><blockquote><a href="https://arxiv.org/abs/1906.08262">Minimal Surfaces and Weak Gravity</a><br /></blockquote>OK, the first name isn't Kevin but I wanted to increase the traffic to arXiv.org. The main reason why the seemingly dull Weak Gravity Conjecture has implications for the higher-dimensional geometry is that the electromagnetic forces may be obtained from rather complex higher-dimensional constructions within string theory.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />They discuss Euclidean D3-brane instantons on 4-cycles of Calabi-Yau three-folds in type IIB string theory. I feel somewhat anxious about the instanton form of the Weak Gravity Conjecture. Liam and others, wouldn't be it at least equally logical to talk about type IIA string theory and D4-branes that wrap four-cycles to produce simple charged and massive particles? That's really the normal way to formulate the Weak Gravity Conjecture.<br /><br />OK, I will use the D4-brane language. If you wrap the D4-brane on a supersymmetric 4-cycle, the attractive gravitational force will be the same – up to an undetermined sign – as the \(U(1)\) repulsive "electric" force where the \(U(1)\) field comes from a contraction of a Ramond-Ramond field over the four-cycle. BPS objects clearly pass the Weak Gravity Conjecture marginally by saturating the inequality.<br /><br />But what about the non-supersymmetric cycles? Elements of the homology that are some general linear combination of holomorphic and antiholomorphic cycles? The mass of a D4-brane wrapped on this general cycle is equal to the tension of the D4-brane times the volume of the 4-cycle. The cycles also produce the electric forces, as I said, and the magnitude of the charge – normalized to make the electric force natural – is given by the Kähler potential,\[<br /><br />\sqrt{\Sigma_i (K^{-1})^{ij} \Sigma_j }.<br /><br />\] The force obeys \[<br /><br />{\rm Re} \,S_\Sigma \leq c ||\Sigma||<br /><br />\] where \(c\) is of order one and they actually determine it to be \(c=\sqrt{3/4}\) for their particular class of examples. I just want to make sure that you don't think that this \(c\) makes the inequality vacuous.<br /><br />OK, the gravitational force must be weaker than the electric one for this non-supersymmetric cycle which means that the minimum-volume submanifold in the non-supersymmetric cohomology class must be smaller than something. They decide that their final inequality is\[<br /><br />{\mathfrak r}_\Sigma \geq {\mathfrak r}_\Sigma^{\rm min} := \frac{2\pi}{c} \frac{{\rm Vol} (\Sigma_\cup)}{||\Sigma||} - 1. \tag{2.11}<br /><br />\] This may become highly nontrivial because the lattice of possible charges may become sparse or very sparse. Even though you have a small amount of freedom to pick the representative, a cycle of a surprisingly low, "sub-Pythagorean" volume is guaranteed to exist.<br /><br />I think their claim is some generalization of a schoolkid's statement that there exists a connection between points \((x,0)\) and \((0,y)\) whose length is at most \(\sqrt{x^2+y^2}\). Except that their statement replaces the linear, flat line intervals \(x\) and \(y\) with some curved submanifolds of a 6-dimensional manifold.<br /><br />An alternative outcome could be, of course, that the Weak Gravity Conjecture is wrong. You could disprove the Weak Gravity Conjecture in a new way if you found a Calabi-Yau manifold and proved that the low-volume four-cycle whose existence they have derived doesn't exist. You must be warned: you're rather unlikely to succeed because such a result would also mean, basically, that our paper is wrong and it is a tall order. ;-) More seriously, there exist conceptual arguments – arguments that come from several lines of reasoning and end up with the same conclusion – that derive the conclusion from some solidly motivated statements about black holes, forces, quantum gravity, and string theory.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-78485748967290266192019-06-20T08:50:00.001+02:002019-06-20T09:02:16.039+02:00Baer et al.: stringy naturalness prefers less usual but accessible SUSY scenarios, risky electroweak symmetry breakingIn early February, I discussed a <a href="https://motls.blogspot.com/2019/02/baer-et-al-string-theory-predicted.html?m=1">paper by Howard Baer and 4 co-authors</a> which made some steps to update the estimates of superpartner masses and other parameters of new physics – by replacing naturalness with the string naturalness which takes "the number of string vacua with certain properties" as a factor that makes a vacuum more likely.<br /><br /><iframe width="407" height="277" src="https://www.youtube.com/embed/frZ9_ZGGf8M" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe><br /><br /><em>Ace of Base, Living in Danger – recorded decades before the intense Islamization of Sweden began. In the eyes of a stranger, such as a Czech, Swedes are surely living in danger. The relevance will become clear later.</em><br /><br />They have claimed that this better notion of naturalness naturally drives cubic couplings \(A\) to large values (because those are more represented in the string vacua, by a power law) which means a large mixing in the top squark sector and stop masses that may exceed \(1\TeV\). Also, the other (first two generation squarks...) scalars are "tens of \({\rm TeV}\) in mass". The lightest two neutralinos should be close to each other, with a mass difference around \(5\GeV\). Most encouraging is the derivation that the Higgs mass could be pushed up towards the observed \(125\GeV\), plus minus one.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />They have continued to publish papers – roughly one paper per month – and the first hep-ph paper today comes from a similar author team, too.<br /><blockquote><a href="https://arxiv.org/abs/1906.07741" rel="nofollow">Naturalness versus stringy naturalness (with implications for collider and dark matter searches)</a><br /></blockquote>I improved the title by closing the parenthesis. Baer, Barger, and Salam review some of the previous claims about the string naturalness – and look which general kinds of supersymmetry scenarios are likely according to the string naturalness.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />String theory and supersymmetry are friends – but they are independent and different, too. Any person who does some actual research about the deeper origin of the observed laws of particle physics (currently the Standard Model) must have some theoretical basis to produce estimated probabilities of various statements about new particles and similar things. If you refuse to consider any such measures or probabilities, it just means that you are a complete non-expert in this part of physics and you shouldn't contaminate the discussions about these topics by your noise.<br /><br />For bottom-up model builders, the "practical naturalness" has been the canonical framework to think about such matters. "Practical naturalness" says that none of the independent terms that add up to a quantity should be much greater in magnitude than the sum – the total quantity. It's a simple, partially justified rule, but it's also too heuristic and may be wrong or highly inaccurate, especially in some special (and perhaps even not so special) conditions.<br /><br />String theory is bound to modify these rules. As I said, it seems that string theory wants the \(A\) cubic couplings to be high and so on. This has other implications. We're being pushed to some more extreme corners of the parameter space – more extreme according to the previous notion of naturalness – and the counting is a bit different in these corners. In particular, some masses may be rather high while this doesn't imply too big a fine-tuning, and so on.<br /><br />Non-stringy supersymmetry model builders have often considered subsets of the MSSM parameter space such as the CMSSM (Constrained Minimal Supersymmetric Standard Model) and mSUGRA (minimum supergravity). These are obvious enough choices to reduce the number of soft parameters in the MSSM with broken supersymmetry. However, Baer et al. present evidence that such vacua are actually rather rare. High scale SUSY breaking models are more frequent but only some kinds. You need to read the paper to see the fate of PeV SUSY, minisplit SUSY, spread SUSY, and others.<br /><br />The stringy counting arguments seem to prefer light enough higgsinos (and the related \(m_{\rm weak}\) parameter) in the vicinity of a hundred or hundreds of \({\rm GeV}\). On the other hand, gluinos and other strongly interacting superpartners are said to be out of the LHC reach.<br /><br />Concerning the Higgs potential which is what breaks the electroweak symmetry, Baer et al. claim that the stringy naturalness pressures push the Universe to "living dangerously". It means that the parameters of these potentials are such that some of the "deadly" features of the potential are relatively nearby. By "deadly" features, I mean potentials that break the electromagnetic \(U(1)\); or they break the color \(SU(3)\); or that don't break the electroweak symmetry at all; or that produce a pocket universe weak scale of a magnitude that is clearly incompatible with the observed one.<br /><br />If they can get this preference for the dangerous life, couldn't they also explain by the stringy statistical arguments why the whole electroweak vacuum seems – due to the other minimum of the Higgs potential etc. – to be metastable and almost unstable? That the quadratic terms in the Higgs potential, when reversed back to the Planck scale, seem to be zero – that the Standard Model seems to be "conformal" in the UV? And other coincidences that people have noticed...<br /><br />At any rate, I find this research inconclusive but very interesting. The reasoning is imperfect but it's still much better than no reasoning or insisting on pure prejudices. And this reasoning indicates that the probability that some new particles such as higgsinos are just "hundreds of \({\rm GeV}\) in mass" and therefore (almost) accessible by the LHC is surely comparable to 50% or higher. The people who claim such a probability to be close to zero are just deluding themselves – they are defending themselves against a totally real possibility that they totally arbitrarily labeled blasphemous.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-63658327266942132512019-06-18T13:35:00.001+02:002019-06-18T13:55:48.605+02:00Acharya: string/M-theory probably implies low-energy SUSY<span class="isolimg"><a href="https://twitter.com/bobbyacharya" rel="nofollow"><img src="https://pbs.twimg.com/profile_images/2896020052/f00b09545bdb6acd97daad7959042e48.jpeg" width=144 align="left"></a></span>Bobby Acharya is a versatile fellow. Whenever you search for the author <a href="http://inspirehep.net/search?ln=en&ln=en&p=find+a+acharya%2Cb&of=hcs&action_search=Search&sf=&so=d&rm=&rg=25&sc=0">Acharya, B</a> on Inspire, you will find out that "he" has written 1,527 papers which have earned over 161,000 citations which would trump 144,000 citations of <a href="http://inspirehep.net/search?ln=en&ln=en&p=find+a+witten%2Ce&of=hcs&action_search=Search&sf=&so=d&rm=&rg=25&sc=0">Witten, E</a>. Much of this weird huge number actually has some merit because Acharya is both a highly mathematical theorist – an expert in physics involving complicated extra-dimensional manifolds – as well as a member of the ATLAS experimental team at the LHC.<br /><br />Today, he published<br /><blockquote><a href="https://arxiv.org/abs/1906.06886">Supersymmetry, Ricci Flat Manifolds and the String Landscape</a>.<br /></blockquote>String theory and supersymmetry are "allies" most of the time. Supersymmetry is a symmetry that first emerged – at least in the Western world – when Pierre Ramond was incorporating fermions to the stringy world sheet. (In Russia, SUSY was discovered independently by purely mathematical efforts to classify Lie-algebra-like physical symmetries.) Also, most of the anti-string hecklers tend to be anti-supersymmetry hecklers as well, and vice versa.<br /><br />On the other hand, string theory and supersymmetry are somewhat independent. Bosonic string theory in \(D=26\) has no SUSY – and SUSY is also broken in type 0 theories, some non-supersymmetric heterotic string theories, non-critical string theory, and more. Also, supersymmetry may be incorporated to non-gravitational field theories, starting with the Wess-Zumino model and the MSSM, which obviously aren't string vacua – because the string vacua make gravity unavoidable.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Some weeks ago, Alessandro Strumia was excited and told us that he wanted to become a non-supersymmetric stringy model builder because it was very important to satisfy one-half of the anti-string, anti-supersymmetric hecklers. It's a moral duty to abandon supersymmetry, he basically argued, so string theorists must do it as well and he wants to lead them. He didn't use these exact words but it was the spirit.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Well, string vacua with low-energy supersymmetry are rather well understood and many of them have matched the observed phenomena with an impressive (albeit not perfect, so far) precision – while those without supersymmetry seem badly understood and their agreement with the observations hasn't been proven too precisely. It's not surprising for many reasons. One of them is that supersymmetry makes physics both more stable, promising, and free of some hierarchy problems which is good phenomenologically; as well as full of cancellations and easier to calculate which is good from a mathematical viewpoint. <a href="https://www.youtube.com/watch?v=mVfsmaf1s9Y" rel="nofollow">Oh, SUSY</a>, with a pictorial walking.<br /><br />It is totally plausible that supersymmetry at low enough energies is an unavoidable consequence of string/M-theory – assuming some reasonably mild assumptions about the realism of the models. This belief was surely shared e.g. by my adviser Tom Banks – one of his prophesies used to be that this assertion (SUSY is unavoidable in string theory or quantum gravity) would eventually be proven. Acharya was looking into this question. <br /><br />He focused on "geometric" vacua that may be described by 10D, 11D, or 12D (F-theory...) supergravity – which may <em>then</em> be dimensionally reduced to a four-dimensional theory. Assuming that these high-dimensional supergravity theories are good approximations at some level, the statement that "supersymmetry is unavoidable in string theory" becomes basically equivalent to the statement that "manifolds used for stringy extra dimensions require covariantly constant spinors".<br /><br />Calabi-Yau three-folds – which, when used in heterotic string theory, gave us the first (and still excellent) class of realistic string compactifications in 1985 – are manifolds of \(SU(3)\) holonomy. This holonomy guarantees the preservation of 1/4 of the supercharges that have existed in the higher-dimensional supergravity theory in the flat space because the generic holonomy \(SU(4)\sim SO(6)\) of the orientable six-dimensional manifolds is reduced to \(SU(3)\) where only 3 spinorial components out of 4 are randomly rotated into each other (after any closed parallel transport) while the fourth one remains fixed.<br /><br />In table 1, Acharya lists all the relevant holonomy groups. If you forgot, the holonomy group is the group of all possible rotations of the tangent space that is induced by a parallel transport around any closed curve.<br /><br />\(SO(N)\) is the generic holonomy of an \(N\)-dimensional real manifold. It would be \(O(N)\) if the manifold were unorientable. This transformation mixes the spinors in the most general way so there are no covariantly constant spinors. But there could nevertheless be Ricci-flat manifolds of this generic holonomy. The three question marks are written on that first line of his table because they exactly correspond to the big question he wants to probe in this paper.<br /><br />Now, in real dimensions \(n=2k\), \(n=4k\), \(n=7\), and \(n=8\), one has the holonomies \(SU(k)\), \(USp(2k)\), \(G_2\), and \(Spin(7)\), respectively. All these special holonomies guarantee covariantly constant spinors i.e. some low-energy supersymmetry; and the Ricci-flatness of the metric, too. On the other hand, one may also "deform" the \(SU(k)\) and \(USp(2k)\) holonomies to \(U(k)\) and \(USp(2k)\times Sp(1)\), respectively, and this deformation kills both the covariantly constant spinors (i.e. SUSY) as well as the Ricci-flatness.<br /><br />Note that string/M-theory allows you to derive Einstein's equations of general relativity from a more fundamental starting point. In the absence of matter sources (i.e. in the vacuum), Einstein's equations reduce to Ricci-flatness i.e. \(R_{\mu\nu}=0\). This is relevant for the curved 4D spacetime that everyone knows. But it's also nice for the extra dimensions that produce the diversity of low-energy fields and particles. <br /><br />So whether you find it beautiful or not, and all physicists with a good taste find it beautiful (and the beauty is very important, I must make you sure about this basic fact because you may have been misled by an ugly pundit), string/M-theory makes it important to study Ricci-flat manifolds – both manifolds including the 4 large dimensions that we know, as well the compactified extra dimensions. The former is relevant for 4D gravity we know; the latter is more relevant for the rest of physics.<br /><br />Acharya divides the question "whether the Ricci-flat manifolds without covariantly constant spinors exist" into two groups:<br /><br />* simply connected manifolds<br />* simply disconnected manifolds<br /><br />In the first group, he doesn't quite find the proof but it seems that he believes that the conjecture that "no such compact, simply connected, Ricci flat manifolds without SUSY exist" seems promising.<br /><br />In the second group, there exist counterexamples. After all, you may take quotients (orbifolds) of some supersymmetric manifolds – but the orbifolding maps the spinors to others in a generic enough way which breaks all of supersymmetry. So SUSY-breaking, Ricci-flat compactifications exist.<br /><br />However, at the same moment, Acharya points out that all such simply disconnected Ricci-flat manifolds seem to suffer from an instability – a generalization of Witten's "bubble of nothing". It's given by a Coleman-style instanton that has a hole inside. The simplest vacuum with this Witten's instability is the Scherk-Schwarz compactification on a circle with antiperiodic boundary conditions for fermions (the easiest quotient-like way to break all of SUSY because when a constant is antiperiodic, it must be zero). The antiperiodic boundary conditions are perfect for closing a cylinder into a cigar (a good shape for Coleman-like instantons in the Euclideanized spacetime, especially because of Coleman's obsessive smoking) on which the spinors are well-behaved.<br /><br />So the corresponding history in the Minkowski space looks like a vacuum decay – except that the new vacuum in the "ball inside" – which is growing almost by the speed of light – isn't really a vacuum at all. It's "emptiness" that doesn't even have a vacuum in it. The radius of the circular dimension – which is \(a\to a_0\) for \(r\to\infty\) – continuously approaches \(r=0\) on the boundary of Witten's bubble of nothing – basically on \(|\vec r|=ct\) where \(c\) is the speed of light – and it stays zero for \(|\vec r|\lt ct\) which means that there's no space for \(|\vec r| \lt ct\) at all.<br /><br />Such instabilities are brutal and Acharya basically proves that these instabilities make all Ricci-flat, simply disconnected, non-supersymmetric stringy compactifications unstable. We see that our Universe doesn't decay instantly so we can't live in such a vacuum. Instead, the extra dimensions should either be supersymmetric and simply disconnected; or they should be simply connected. When they're simply connected, the conjecture – which has passed lots of tests and may be proven – says that these compactifications imply low-energy supersymmetry, anyway.<br /><br />If this conjecture happened to be wrong, it would seem likely to Acharya – and me – that the number of non-supersymmetric, simply connected, Ricci-flat compact manifolds would probably be much higher than the number of the supersymmetric Ricci-flat solutions. If it were so, SUSY breaking could be "generic" in string/M-theory, and SUSY breaking could actually become a rather solid prediction of string/M-theory. (Well, the population advantage should also beat the factor of \(10^{34}\) to persuade us that we don't need to care about the non-supersymmetric vacua's hierarchy problem.) Note that with some intense enough mathematical work, it should be possible to settle which of these two predictions are actually being made by string theory.<br /><br />Acharya has only considered "geometric/supergravity" vacua. It's possible that some non-geometric vacua not admitting a higher-dimensional supergravity description are important or numerous or prevailing – and if it is so, the answer about low-energy SUSY could be anything and Acharya's work could become useless for finding this answer.<br /><br />But some geometric approximation may exist for almost all vacua - dualities indicate that there are often <em>several</em> geometric starting points to understand a vacuum, so why the number should be zero too often? – and the incomplete evidence indicates that low-energy SUSY is mathematically needed in stable enough string vacua. When I say low-energy SUSY, it may be broken at \(100\TeV\) or anything. But it should be a scale lower than the Kaluza-Klein scale of the extra dimensions – and maybe than some other, even lower, scales.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-88982114939145582572019-06-17T09:07:00.000+02:002019-06-17T17:15:29.212+02:00μνSSM produces nice neutrino masses, new 96 GeV HiggsThe most interesting new hep-ph preprint is<br /><blockquote><a href="https://arxiv.org/abs/1906.06173">Precise prediction for the Higgs-Boson Masses in the μνSSM with three right-handed neutrino superfields</a> (58 pages)<br /></blockquote>by Sven Heinemeyer (CERN) and Biekötter+Muñoz (Spain) – BHM. They discuss some remarkable combined virtues of a non-minimal supersymmetric model of particle physics.<br /><br /><span class="noborimg"><img src="https://lh3.ggpht.com/_4ruQ7t4zrFA/SvvuBKO7CNI/AAAAAAAADf8/z6dXJfhzbiI/susy.jpg"></span><br /><br />Note that none of the so far observed elementary particles – bosons or fermions – seems to be a superpartner of another observed fermion or boson, respectively. But for theoretical reasons, it is more likely that these superpartners exist and a supersymmetric Standard Model is a more accurate description of Nature than the Standard Model – the minimum model encompassing the currently observed particles.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />From a string theorist's, top down perspective, there may exist many different supersymmetric models that are relevant at low energies (energies accessible by colliders), with or without grand unification, with or without various hidden sectors. String theory or more generally quantum gravity surely guarantees an infinite number of very massive particle species – that gradually become generic black hole microstates once their mass is above or well above the Planck mass.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />But from a bottom-up perspective, what are the first new particles that are likely to be observed? The golden standard extension of the Standard Model is the MSSM, the Minimal Supersymmetric Standard Model. Take all particles of the Standard Model, extend them to a superfield (the superpartner has a spin lower by 1/2, except for the superpartners of scalars that need to go to +1/2, of course), and add all the new couplings compatible with supersymmetry. <br /><br />Because you find out that the Higgs superfield is chiral, you will need to double the number of Higgs fields – to have two doublets, each of which is also a superfield – to produce the masses for up-type as well as down-type quarks. This doubling of the Higgses is also necessary to cancel some anomalies that would otherwise arise from the new chiral higgsinos. As far as physical particles go, you will get 5 Higgses (8-3, 3 are eaten by the gauge bosons to become massive and gain a longitudinal polarization): the normal CP-even Higgs, its lighter sibling, the CP-odd neutral boson, and a particle-antiparticle pair of charged Higgses. The higgsinos are mixed with photinos and zinos to give you four neutralinos; while the charged higgsinos mix with the winos to produce two charginos.<br /><br />Aside from other virtues, the MSSM is better (because less unnaturally fine-tuned) than the Standard Model because it eliminates all of the hierarchy problem or most of it – if the superpartners are light enough, they cancel the potentially huge loop corrections to the Higgs mass, with some precision. Also, MSSM is usually (but not always) considered with an unbroken R-parity (the number of new superpartners modulo two) which makes the lightest superpartner, the LSP, stable and an excellent candidate for dark matter.<br /><br />In the MSSM, the self-interaction of the Higgses arises due to a cubic superpotential which has a coefficient \(\mu\). This \(\mu\) could also be expected to be large and there's a milder, new hierarchy-like problem, the \(\mu\)-problem. The most trusted supersymmetric model beyond the MSSM is the NMSSM, the Next-To-Minimal Supersymmetric Standard Model which upgrades this parameter \(\mu\) into a new superfield \(S\), a new singlet Higgs superfield. The \(\mu\)-problem is avoided and the NMSSM has some other advantages.<br /><br />BHM argue that another supersymmetric extension of the Standard Model, the mu-from-nu SSM or μνSSM, should be considered the "third most canonical" supersymmetric extension of the Standard Model if not better. The μνSSM also has a new superfield \(\mu\) which plays the same role as \(\mu\) in NMSSM. However, in μνSSM, the fermionic components of this new field is simultaneously the right-handed neutrino. So the new singlet Higgses and right-handed neutrinos are unified into a superfield, a nice and economic choice to exploit the available chairs in the superfields – it's nice if it can be compatible with observations. And it can, they argue.<br /><br />The neutrino masses have the right magnitude because the electroweak seesaw mechanism naturally follows from the equations. The R-parity is broken but a long-lived gravitino seems like a good dark matter candidate (which is invisible to the direct searches). Also, BHM seem convinced by the mathematics that there is no reason for a "flavor blindness" of the parameters in this model. You might be afraid of flavor-changing predictions but they say that with the constraints on the neutrino mass matrices, these FCNC-like predictions are within the experimental bounds.<br /><br />Because we have three generations of neutrinos, it's natural to have three new \(\mu\)-like superfields with three right-handed neutrinos and three new singlet Higgs fields. In this new paper, for the first time, BHM consider the full model with three such new \(\mu\)-fields. And with the help of some software, they also analyze the full one-loop diagrams and the equally accurate renormalization group flows to say something about the masses. Note that the loop diagrams matter in supersymmetric models – for example, even in the MSSM, they are vital to increase the tree-level prediction of the Higgs mass from \(83\GeV\) to \(125\GeV\). The loop diagrams fulfill some additional tasks in the μνSSM.<br /><br />As a great by-product, the <a href="https://motls.blogspot.com/search?q=Higgs+96&m=1&by-date=true">preliminary \(96\GeV\) Higgs boson</a> indicated by some diphoton and bottom-pair excesses at LEP and CMS, may be one of the mass bosonic eigenstates of these new \(\mu\)-fields (sneutrinos). In some other section, they discuss quite a precise setup with sneutrino masses near \(1235\GeV\), this precision is sort of intriguing. I didn't understand whether these very different values of the sneutrino masses follow from one scenario or two.<br /><br />The folks seem genuinely excited about the \(96\GeV\) excess and waiting for new clues about these experimental hints. I am somewhat excited, too – but they're excited enough to find the energy to write 58 pages on calculations in a potentially relevant model.<br /><br /><iframe width="407" height="277" src="https://www.youtube.com/embed/ZPAYQyu7lo0" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe><br /><br />Because we discussed fake Spaniards with Erwin, here is a Czech remake "A lamb and a wolf" of a random medieval Spanish Christmas carol <a href="https://www.youtube.com/watch?v=g67k0g4oILo">Riu Riu Chiu</a> – which, as you will probably agree, is better than the Spanish original song. From the 1990 album "<a href="https://www.youtube.com/watch?v=hQfqJNvdemQ" rel="nofollow">You have to insist on your truth</a>" – byt the Spiritual Quintet band, when brothers Nedvěd were members (the membership seems frequently changing). This band isn't quite mainstream on radios but most Czechs are familiar with this kind of music which dominates the campfires (although the Spiritual Quintet clearly sings more religious music than the most famous songs by the Nedvěd brothers and similar musicians). Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-77688644933081119612019-06-09T13:46:00.000+02:002019-06-09T14:21:06.095+02:00Direct anthropic bound on the weak scale from supernovæ explosions – or how I learned to stop worrying and love the Higgs<em>Guest blog by Prof Alessandro Strumia, not only a famous misogynist but also a physicist ;-)</em><br /><br /><span class="isolimg"><img src="https://ichef.bbci.co.uk/news/624/cpsprodpb/EBC0/production/_105925306_whatsubject.jpg" width=144 align="left"></span>I thank Luboš for hosting this post, where I present a strangelove-like idea that might be the long-sought explanation of the most puzzling aspect of the Standard Model (SM) of the Fundamental Interactions: the existence of two vastly different mass scales. The electro-weak Fermi scale (set by the Higgs mass, that controls the mass of all other elementary Standard Model particles) is 17 orders of magnitude smaller than the gravitational Planck scale (the mass above which any elementary particle is a black hole, according to Einstein Relativity and Quantum Mechanics).<br /><br />The puzzle is that, according to many theorists, the Standard Model Higgs is unnatural because its squared mass receives Planck-scale quantum corrections, so that cancellations tuned by one part in \(10^{34}\) are needed to get the small Fermi scale. This naturalness argument lead theorists to expect that the Higgs cannot be alone, that it must exist together with new physics that protects its lightness. Theorists proposed concrete examples of new physics that makes the Higgs natural: supersymmetry, technicolor, extra dimensions... Dozens of thousands of research publications studied these ideas and supersymmetry seemed to work so beautifully that most theorists expected that the Fermi scale is the scale of supersymmetry breaking.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />The physics of the fundamental interactions enjoyed a decennium of great interest, returning to be a data-driven field, when in 2010 the Large Hadron Collider (LHC) started to explore physics above the Fermi scale. Experiments could finally answer the biggest question identified in decades of theoretical speculations: the origin of the Fermi scale.<br /><br />The dominant expectation, based on naturalness, was that the LHC would have opened a golden age for high-energy physics, discovering the Higgs boson together with the new physics that protects its lightness. Some theorists worried that too much new physics could be a background to itself. <br /><br />This is no longer a worry: LHC discovered the Higgs and no new physics. Data agree with the Standardissimo Model. The lack of supersymmetry and of any other new physics that makes the Fermi scale “natural” is now considered as a serious issue.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Unnaturalness is so important that, before accepting such conclusion, one would like to check that it persists at higher energies. But LHC already reached 13 TeV and most of its discovery potential has been exploited. No higher-energy collider is in construction. Getting funds for reaching higher energies and possibly finding more nothing is difficult: a new 100 TeV collider seem to cost 29 billions of dollars. It's a lot of money. We're gonna have to earn it. <a href="https://arxiv.org/abs/1906.02693">A paper on arXiv today</a> includes gender as motivation for giving it to CERN. Supersymmetry would have been a better motivation: that's why before LHC physicists dubbed the present situation as “nightmare scenario”. Waiting for 100 TeV data at my 100th birthday, I provisionally assume that present negative results from LHC mean that the Fermi scale is unnatural.<br /><br />Crisis can lead to progress. It is maybe not exaggerated to see a parallel between the present negative results from LHC and the negative results of the Michelson-Morley experiment, that in 1887 shacked the strong belief in the ugly aether theory, opening a crisis later beautifully resolved by relativity. Today we are confused about naturalness. Nature is surely following some logic. Marx said that «history repeats itself, first as tragedy, then as farce». So maybe this time nature follows a ugly logic missed by physicists who seek something beautiful.<br /><br />The unnatural smallness of the Fermi scale could be due to anthropic selection. The A-word is not politically correct among physicists, but anthropic selection is like <a href="https://www.laphamsquarterly.org/magic-shows/miscellany/niels-bohrs-lucky-horseshoe">the horseshoe of Bohr</a>: it works even when physicists don't believe in it.<br /><br />Anthropic selection might sound science fiction, but it easily follows from our present theoretical understanding of physics. All what is needed is a theory (possibly string theory) that admits as minima of its potential a “landscape” of many vacua (say, \(10^{500}\)) with different values of their vacuum energy and of their Fermi scale (more in general with different particle physics, as particles are excitations around the vacuum). Thanks to enough diversity, rare vacua have “good” physical laws that allow for complex nuclei, chemistry, stars... and life and observers. Thanks to cosmological inflation, different vacua are realised in different regions of space-time, separated by deserts and walls (known as “cosmological horizons” and “potential barriers”). Thanks to diversity plus separation, our universe can be a region in one “good” vacuum immersed in a bigger “multiverse” of shi**ole regions. As “life” can only form in rare regions with “good” physics, observers worry about naturalness because they measure fundamental constant that seem tuned for their existence, but not more tuned than that.<br /><br />Weinberg in 1987 proposed an anthropic argument for the smallness of the cosmological constant. Agrawal, Barr, Donoghue and Seckel in 1997 noticed that light fermion masses \(m_f\) have special values that allow for the possible existence of many nuclei, rather than just Hydrogen and/or Helium. More complex chemistry seems needed for “life”. However this anthropic boundary does not explain the smallness of the Fermi scale \(v\), because fermion masses are obtained in the Standard Model as \(m_f=y_f v\) (dimension-less Yukawa couplings \(y_f\) times Fermi scale \(v\)): a SM-like vacuum with the same “good” fermion masses obtained from bigger Fermi scale \(v\) times smaller Yukawas \(y_f\) needs less tuning, and would thereby be more likely in a multiverse. So far the Standard Model seems uselessly unnatural even if fermion masses are anthropically selected.<br /><br />An anthropic explanation of the smallness of the Fermi scale needs an anthropic boundary that directly restricts the Fermi scale. In order to search for such extra boundary, we look at events where weak interactions play a key role. There are two events where non-trivial physics happens thanks to the same numerical coincidence\[<br /><br />v\sim M_{\rm Planck}^{1/4} \Lambda_{\rm QCD}^{3/4}<br /><br />\] that involves the Fermi scale, the Planck mass and the naturally small QCD scale (or proton mass).<br /><br />The first event is Big Bang Nucleosynthesis: Hall, Pinner and Ruderman showed in 2014 that BBN produces comparable Hydrogen and Helium abundances because neutrinos decouple at a temperature comparable to the proton/neutron mass difference, and because BBN happens when the age of the Universe is 3 minutes, comparable to the neutron life-time. This is puzzling, but it does not seem to lead to an anthropic boundary.<br /><br />The second event is core-collapse supernova explosions. According to their standard theoretical understanding (partially validated by the 1987 observation of supernova neutrinos), explosions happen because weak interactions of outflowing neutrinos push the material outwards. This pushing is effective because neutrinos are trapped for a few seconds, a time comparable to the gravitational time-scale of a supernova. We argued that explosions disappear if the Fermi scale \(v\) is changed by a factor of few in either direction. If \(v\) is too small, neutrinos are too much trapped and exit too late when the collapse is over. If \(v\) is too large, neutrinos are not trapped and immediately fly away with negligible weak interactions.<br /><br /><iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/aysiMbgml5g/0.jpg" frameborder="0" height="288" src="https://www.youtube.com/embed/aysiMbgml5g?feature=player_embedded" width="407"></iframe><br /><br />Core-collapse supernova explosions spread intermediate-mass elements that seem needed by “life”, such as Oxygen. This is illustrated by the following periodic table, where elements are colored according to what produces them, and primary and secondary elements that seem needed by the chemistry of “life” are highlighted.<br /><br /><a href="https://1.bp.blogspot.com/-np9wLzvVa8w/XPzIEUZzekI/AAAAAAAAAAg/dGUEX7T7eoASF5xArI6G8hbaujAdkFllwCLcBGAs/s1600/PeriodicTable.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="569" data-original-width="1600" height="141" src="https://1.bp.blogspot.com/-np9wLzvVa8w/XPzIEUZzekI/AAAAAAAAAAg/dGUEX7T7eoASF5xArI6G8hbaujAdkFllwCLcBGAs/s400/PeriodicTable.jpg" width="400" /></a><br /><br />Core-collapse supernova explosions (in green) seem anthropically relevant.<br /><br />In conclusion, we might observe an unnaturally small value of the Fermi scale because of anthropic selection: no observers exist in universes where the Fermi scale has larger, more natural, values.<br /><br />I over-simplified: scientific details and doubts can be found in <a href="https://www.cp3-origins.dk/tube/how-i-learned-to-stop-worrying-and-love-the-higgs">this talk</a> and in <a href="https://arxiv.org/abs/1906.00986">this arXiv preprint</a> in collaboration with D'Amico, Urbano and Xue. We are high-energy physicists, not experts of supernova explosions nor of astro-biology. I hope that experts can better test the idea: it's important because it might explain the smallness of the Fermi scale, and this is a major topic in fundamental physics since decades.<br /><br />Actually (despite my jokes) this is a deadly serious topic. Fundamental physics now risks abandoning the high-energy frontier. But our scientific job is seeking the correct understanding, even if it means losing our job.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-48971469986085988772019-06-01T08:06:00.000+02:002019-06-01T08:40:31.741+02:00Wolfram on Gell-Mann<span class="isolimg"><a href="https://twitter.com/stephen_wolfram" rel="nofollow"><img src="https://pbs.twimg.com/profile_images/809067753890050049/UpC1-Kjf_200x200.jpg" width=144 align="left"></a></span>I got a permission to post a very interesting text by <a href="https://www.stephenwolfram.com/">Stephen Wolfram</a> so if you're thirsty for some intellectual adrenaline and if you can survive without tons of writers' humility ;-), keep on reading.<br /><br /><b>Remembering Murray Gell-Mann (1929–2019), Inventor of Quarks</b><br /><em>Guest blog by Stephen Wolfram</em><br /><br /><b>First Encounters</b><br /><br />In the mid-1970s, particle physics was hot. Quarks were in. Group theory was in. Field theory was in. And so much progress was being made that it seemed like the fundamental theory of physics might be close at hand.<br /><br />Right in the middle of all this was Murray <a href="https://www.wolframalpha.com/input/?t=crmtb01&f=ob&i=murray+gell-mann" rel="nofollow">Gell-Mann</a>—responsible for not one, but most of the leaps of intuition that had brought particle physics to where it was. There’d been other theories, but Murray’s—with their somewhat elaborate and abstract mathematics—were always the ones that seemed to carry the day.<br /><br />It was the spring of 1978 and I was 18 years old. I’d been <a href="https://www.stephenwolfram.com/publications/academic/?cat=particle-physics" rel="nofollow">publishing papers on particle physics</a> for a few years, and had gotten quite known around the international particle physics community (and, yes, it took decades to live down my teenage-particle-physicist persona). I was in England, but planned to soon go to graduate school in the US, and was choosing between Caltech and Princeton. And one weekend afternoon when I was about to go out, the phone rang. In those days, it was obvious if it was an international call. “This is Murray Gell-Mann”, the caller said, then launched into a monologue about why Caltech was the center of the universe for particle physics at the time.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Perhaps not as starstruck as I should have been, I asked a few practical questions, which Murray dismissed. The call ended with something like, “Well, we’d like to have you at Caltech”.<br /><br />A few months later I was indeed at Caltech. I remember the evening I arrived, wandering around the empty 4th floor of <a href="https://twitter.com/stephen_wolfram/status/1106688232299864065" rel="nofollow">Lauritsen Lab</a>—the home of Caltech theoretical particle physics. There were all sorts of names I recognized on office doors, and there were two offices that were obviously the largest: “M. Gell-Mann” and “<a href="https://www.stephenwolfram.com/publications/short-talk-about-richard-feynman/" rel="nofollow">R. Feynman</a>”. (In between them was a small office labeled “H. Tuck”—which by the next day I’d realized was occupied by Helen Tuck, the lively longtime departmental assistant.)<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />There was a regular Friday lunch in the theoretical physics group, and as soon as a Friday came around, I met Murray Gell-Mann there. The first thing he said to me was, “It must be a culture shock coming here from England”. Then he looked me up and down. There I was in an unreasonably bright yellow shirt and sandals—looking, in fact, quite Californian. Murray seemed embarrassed, mumbled some pleasantry, then turned away.<br /><br /><b>With Murray at Caltech</b><br /><br />I never worked directly with Murray (though he would later describe me to others as “our student”). But I interacted with him frequently while I was at Caltech. He was a strange mixture of gracious and gregarious, together with austere and combative. He had an expressive face, which would wrinkle up if he didn’t approve of what was being said.<br /><br />Murray always had people and things he approved of, and ones he didn’t—to which he would often give disparaging nicknames. (He would always refer to solid-state physics as “squalid-state physics”.) Sometimes he would pretend that things he did not like simply did not exist. I remember once talking to him about something in quantum field theory called the <a href="https://en.wikipedia.org/wiki/Beta_function_(physics)" rel="nofollow">beta function</a>. His face showed no recognition of what I was talking about, and I was getting slightly exasperated. Eventually I blurted out, “But, Murray, didn’t you invent this?” “Oh”, he said, suddenly much more charming, “You mean g times the psi function. Why didn’t you just say that? Now I understand”. Of course, he had understood all along, but was being difficult about me using the “beta function” term, even though it had by then been standard for years.<br /><br />I could never quite figure out what it was that made Murray impressed by some people and not others. He would routinely disparage physicists who were destined for great success, and would vigorously promote ones who didn’t seem so promising, and didn’t in fact do well. So when he promoted me, I was on the one hand flattered, but on the other hand concerned about what his endorsement might really mean.<br /><br />The interaction between Murray Gell-Mann and <a href="https://www.stephenwolfram.com/publications/short-talk-about-richard-feynman/" rel="nofollow">Richard Feynman</a> was an interesting thing to behold. Both came from New York, but Feynman relished his <a href="https://www.youtube.com/watch?v=E1RqTP5Unr4" rel="nofollow">“working-class” New York accent</a>, while Gell-Mann affected the best pronunciation of words from any language. Both would make surprisingly childish comments about the other.<br /><br />I remember Feynman insisting on telling me the story of the origin of the word “quark”. He said he’d been talking to Murray one Friday about these hypothetical particles, and in their conversation they’d needed a name for them. Feynman told me he said (no doubt in his characteristic accent), “Let’s call them ‘quacks’”. The next Monday he said Murray came to him very excited and said he’d <a href="https://archive.org/details/finneganswake00joycuoft/page/n777" rel="nofollow">found the word “quark” in James Joyce</a>. In telling this to me, Feynman then went into a long diatribe about how Murray always seemed to think the names for things were so important. “Having a name for something doesn’t tell you a damned thing”, Feynman said. (Having now spent so much of my life as a <a href="https://blog.stephenwolfram.com/2019/05/what-weve-built-is-a-computational-language-and-thats-very-important/" rel="nofollow">language designer</a>, <a href="https://blog.stephenwolfram.com/2010/10/the-poetry-of-function-naming/" rel="nofollow">I might disagree</a>). Feynman went on, mocking Murray’s concern for things like what different birds are called. (Murray was an avid bird watcher.)<br /><br />Meanwhile, Feynman had worked on particles which seemed (and turned out to be) related to quarks. Feynman had called them “<a href="https://www.stephenwolfram.com/publications/academic/model-parton-showers-qcd.pdf">partons</a>”. Murray insisted on always referring to them as “put-ons”.<br /><br />Even though in terms of longstanding contributions to particle physics (if not physics in general) Murray was the clear winner, he always seemed to feel as if he was in the shadow of Feynman, particularly with Feynman’s showmanship. When Feynman died, Murray wrote a <a href="https://authors.library.caltech.edu/60328/1/1.881192.pdf">rather snarky obituary</a>, saying of Feynman: “He surrounded himself with a cloud of myth, and he spent a great deal of time and energy generating anecdotes about himself”. I never quite understood why Murray—who could have gone to any university in the world—chose to work at Caltech for 33 years in an office two doors down from Feynman.<br /><br />Murray cared a lot about what people thought of him, but would routinely (and maddeningly to watch) put himself in positions where he would look bad. He was very interested in—and I think very knowledgeable about—words and languages. And when he would meet someone, he would make a point of regaling them with information about the origin of their name (curiously—as I learned only years later—his own name, “Gell-Mann”, had been “upgraded” from “Gellmann”). Now, of course, if there’s one word people tend to know something about, it’s their own name. And, needless to say, Murray sometimes got its origins wrong—and was very embarrassed. (I remember he told a friend of mine named <a href="https://www.wolframalpha.com/input/?t=crmtb01&f=ob&i=nathan+isgur" rel="nofollow">Nathan Isgur</a> a long and elaborate story about the origin of the name “Isgur”, with Nathan eventually saying: “No, it was made up at Ellis Island!”.)<br /><br />Murray wasn’t particularly good at reading other people. I remember in early 1982 sitting next to Murray in a limo in Chicago that had just picked up a bunch of scientists for some event. The driver was reading the names of the people he’d picked up over the radio. Many were complicated names, which the driver was admittedly butchering. But after each one, Murray would pipe up, and say “No, it’s said ____”. The driver was getting visibly annoyed, and eventually I said quietly to Murray that he should stop correcting him. When we arrived, Murray said to me: “Why did you say that?” He seemed upset that the driver didn’t care about getting the names right.<br /><br />Occasionally I would ask Murray for advice, though he would rarely give it. When I was <a href="https://www.wolframscience.com/nks/notes-2-3--my-work-on-cellular-automata/">first working on one-dimensional cellular automata</a>, I wanted to find a good name for them. (There had been several <a href="https://www.wolframscience.com/nks/notes-2-3--history-of-cellular-automata/" rel="nofollow">previous names for the 2D case</a>, one of which—that I eventually settled on—was “cellular automata”.) I considered the name “polymones” (somehow reflecting <a href="https://blog.stephenwolfram.com/2013/05/dropping-in-on-gottfried-leibniz/" rel="nofollow">Leibniz’s monad concept</a>). But I asked Murray—given all his knowledge of words and languages—for a suggestion. He said he didn’t think polymones was much good, but didn’t have any other suggestion.<br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=1944183051&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>When I was <a href="https://blog.stephenwolfram.com/2013/06/there-was-a-time-before-mathematica/">working on SMP</a> (a forerunner of <a href="http://www.wolfram.com/mathematica">Mathematica</a> and the <a href="https://www.wolfram.com/language/">Wolfram Language</a>) I asked Murray about it, though at the time I didn’t really understand as I do now the <a href="https://blog.stephenwolfram.com/2019/05/what-weve-built-is-a-computational-language-and-thats-very-important/" rel="nofollow">correspondences between human and computational languages</a>. Murray was interested in trying out SMP, and had a computer terminal installed in his office. I kept on offering to show him some things, but he kept on putting it off. I later realized that—bizarrely to me—Murray was concerned about me seeing that he didn’t know how to type. (By the way, at the time, few people did—which is, for example, why SMP, like Unix, had cryptically short command names.)<br /><br />But alongside the brush-offs and the strangeness, Murray could be personally very gracious. I remember him inviting me several times to his house. I never interacted with either of his kids (who were both not far from my age). But I did interact with his wife, Margaret, who was a very charming English woman. (As part of his dating advice to me, Feynman had explained that both he and Murray had married English women because “they could cope”.)<br /><br />While I was at Caltech, Margaret got very sick with cancer, and Murray threw himself into trying to find a cure. (He blamed himself for not having made sure Margaret had had more checkups.) It wasn’t long before Margaret died. Murray invited me to the memorial service. But somehow I didn’t feel I could go; even though by then I was on the faculty at Caltech, I just felt too young and junior. I think Murray was upset I didn’t come, and I’ve felt guilty and embarrassed about it ever since.<br /><br />Murray did me quite a few favors. He was an original board member of the <a href="https://www.macfound.org/">MacArthur Foundation</a>, and I think was instrumental in getting me a <a href="https://www.macfound.org/fellows/93/">MacArthur Fellowship</a> in the very first batch. Later, when I ran into trouble with intellectual property issues at Caltech, Murray went to bat for me—attempting to intercede with his longtime friend <a href="https://www.wolframalpha.com/input/?i=marvin+goldberger" rel="nofollow">Murph Goldberger</a>, who was by then president of Caltech (and who, before Caltech, had been a professor at Princeton, and had encouraged me to go to graduate school there).<br /><br />I don’t know if I would call Murray a friend, though, for example, after Margaret died, he and I would sometimes have dinner together, at random restaurants around Pasadena. It wasn’t so much that I felt of a different generation from him (which of course I was). It was more that he exuded a certain aloof tension, that made one not feel very sure about what the relationship really was.<br /><br /><b>A Great Time in Physics</b><br /><br />At the end of World War II, the Manhattan Project had just happened, the best and the brightest were going into physics, and “subatomic particles” were a major topic. Protons, neutrons, electrons and photons were known, and together with a couple of hypothesized particles (neutrinos and pions), it seemed possible that the story of elementary particles might be complete.<br /><br />But then, first in cosmic rays, and later in particle accelerators, new particles started showing up. There was the <a href="https://www.wolframalpha.com/input/?i=muon" rel="nofollow">muon</a>, then the <a href="https://www.wolframalpha.com/input/?i=meson" rel="nofollow">mesons</a> (<a href="https://www.wolframalpha.com/input/?i=pions" rel="nofollow">pions</a> and <a href="https://www.wolframalpha.com/input/?i=K0,+K%2B" rel="nofollow">kaons</a>), and the <a href="https://www.wolframalpha.com/input/?i=hyperon" rel="nofollow">hyperons</a> (<a href="https://www.wolframalpha.com/input/?i=lambda+hyperon" rel="nofollow">Λ</a>, <a href="https://www.wolframalpha.com/input/?i=sigma-+,+sigma0,+sigma%2B" rel="nofollow">Σ</a>, <a href="https://www.wolframalpha.com/input/?i=cascade+hyperons" rel="nofollow">Ξ</a>). All were unstable. The muon—which basically <a href="https://www.wolframscience.com/nks/notes-9-14--history-of-elementary-particles/" rel="nofollow">nobody understands even today</a>—was like a heavy electron, interacting mainly through electromagnetic forces. But the others were subject to the strong nuclear force—the one that binds nuclei together. And it was observed that this force could generate these particles, though always together (Λ with K, for example). But, mysteriously, the particles could only decay through so-called weak interactions (of the kind involved in radioactive beta decay, or the decay of the muon).<br /><br />For a while, nobody could figure out why this could be. But then around 1953, Murray Gell-Mann came up with an explanation. Just as particles have “<a href="https://en.wikipedia.org/wiki/Quantum_number">quantum numbers</a>” like spin and charge, he hypothesized that they could have a new quantum number that he called <a href="https://en.wikipedia.org/wiki/Strangeness">strangeness</a>. Protons, neutrons and pions would have zero strangeness. But the Λ would have strangeness –1, the (positive) kaon strangeness +1, and so on. And total strangeness, he suggested, might be conserved in strong (and electromagnetic) interactions, but not in <a href="https://www.stephenwolfram.com/publications/early-books/introduction-weak-interaction-volume-one.pdf" rel="nofollow">weak interactions</a>. To suggest a fundamentally new property of particles was a bold thing to do. But it was correct: and immediately Murray was able to explain lots of things that had been observed.<br /><br />But how did the weak interaction that was—among other things—responsible for the decay of Murray’s “strange particles” actually work? In 1957, in their one piece of collaboration in all their years together at Caltech, Feynman and Gell-Mann introduced the so-called V-A theory of the weak <a href="https://www.stephenwolfram.com/publications/early-books/introduction-weak-interaction-volume-one.pdf">interaction</a>—and, once again, despite initial experimental evidence to the contrary, it turned out to be correct. (The theory basically implies that neutrinos can only have left-handed helicity, and that weak interactions involve parity conservation and parity violation in equal amounts.)<br /><br />As soon as the quantum mechanics of electrons and other particles was formulated in the 1920s, people started wondering about the quantum theory of fields, particularly the electromagnetic field. There were issues with infinities, but in the late 1940s—in Feynman’s big contribution—these were handled through the concept of <a href="https://en.wikipedia.org/wiki/Renormalization">renormalization</a>. The result was that it was possible to start computing things using <a href="https://en.wikipedia.org/wiki/Quantum_electrodynamics">quantum electrodynamics</a> (QED)—and soon all sorts of spectacular agreements with experiment had been found.<br /><br />But all these computations worked by looking at just the first few terms in a series expansion in powers of the interaction strength parameter α≃1/137. In 1954, during his brief time at the University of Illinois (from which he went to the University of Chicago, and then Caltech), Murray, together with <a href="https://en.wikipedia.org/wiki/Francis_E._Low">Francis Low</a>, wrote a paper entitled “Quantum Electrodynamics at Small Distances” which was an attempt to explore QED to all orders in α. In many ways this paper was ahead of its time—and 20 years later, the “renormalization group” that it implicitly defined became very important (and the psi function that it discussed was replaced by the beta function).<br /><br />While QED could be investigated through a series expansion in the small parameter α≃1/137, no such program seemed possible for the strong interaction (where the effective expansion parameter would be ≃1). So in the 1950s there was an attempt to take a more holistic approach, based on looking at the whole so-called <a href="https://en.wikipedia.org/wiki/S-matrix">S-matrix</a> defining overall scattering amplitudes. Various properties of the S-matrix were known—notably analyticity with respect to values of particle momenta, and so-called crossing symmetry associated with exchanging particles and antiparticles.<br /><br />But were these sufficient to understand the properties of strong interactions? Throughout the 1960s, attempts involving more and more elaborate mathematics were made. But things kept on going wrong. The <a href="https://www.wolframalpha.com/input/?t=crmtb01&f=ob&i=proton-proton+total+cross-section" rel="nofollow">proton-proton total interaction probability</a> was supposed to rise with energy. But experimentally it was seen to level off. So a new idea (the <a href="https://en.wikipedia.org/wiki/Pomeron">pomeron</a>) was introduced. But then the interaction probability was found to start rising again. So another phenomenon (multiparticle “cuts”) had to be introduced. And so on. (Ironically enough, early string theory spun off from these attempts—and today, after decades of disuse, S-matrix theory is coming back into vogue.)<br /><br />But meanwhile, there was another direction being explored—in which Murray Gell-Mann was centrally involved. It all had to do with the group-theory-meets-calculus concept of <a href="https://www.wolframalpha.com/input/?i=Lie+groups" rel="nofollow">Lie groups</a>. An example of a Lie group is the 3D rotation group, known in Lie group theory as SO(3). A central issue in Lie group theory is to find representations of groups: finite collections, say of matrices, that operate like elements of the group.<br /><br />Representations of the rotation group had been used in atomic physics to deduce from rotational symmetry a characterization of possible spectral lines. But what Gell-Mann did was to say, in effect, “Let’s just imagine that in the world of elementary particles there’s some kind of internal symmetry associated with the Lie group SU(3). Now use representation theory to characterize what particles will exist”.<br /><br />And in 1961, he published his <a href="https://en.wikipedia.org/wiki/Eightfold_way_(physics)">eightfold way</a> (named after <a href="https://en.wikipedia.org/wiki/Noble_Eightfold_Path">Buddha’s Eightfold Way</a>) in which he proposed—periodic-table style—that there should be 8+1 types of mesons, and 10+8 types of <a href="https://www.wolframalpha.com/input/?i=baryon" rel="nofollow">baryons</a> (hyperons plus <a href="https://www.wolframalpha.com/input/?i=nucleons" rel="nofollow">nucleons</a>, such as proton and neutron). For the physics of the time, the mathematics involved in this was quite exotic. But the known particles organized nicely into Gell-Mann’s structure. And Gell-Mann made a prediction: that there should be one additional type of hyperon, that he called the <a href="https://www.wolframalpha.com/input/?i=omega+minus" rel="nofollow">Ω<sup>–</sup></a>, with strangeness –3, and certain mass and decay characteristics.<br /><br />And—sure enough—in 1964, the was observed, and Gell-Mann was on his way to the <a href="https://www.nobelprize.org/prizes/physics/1969/summary/">Nobel Prize</a>, which he received in 1969.<br /><br />At first the SU(3) symmetry idea was just about what particles should exist. But Gell-Mann wanted also to characterize interactions associated with particles, and for this he introduced what he called <a href="https://en.wikipedia.org/wiki/Current_algebra">current algebra</a>. And, by 1964, from his work on current algebra, he’d realized something else: that his SU(3) symmetry could be interpreted as meaning that things like protons were actually composed of something more fundamental—that he called <a href="https://en.wikipedia.org/wiki/Quark">quarks</a>.<br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=1579550126&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>What exactly were the quarks? In his first paper on the subject, Gell-Mann called them “mathematical entities”, although he admitted that, just maybe, they could actually be particles themselves. There were problems with this, though. First, it was thought that electric charge was quantized in units of the electron charge, but quarks would have to have charges of 2/3 and –1/3. But even more seriously, one would have to explain why no free quarks had ever been seen.<br /><br />It so happened that right when Gell-Mann was writing this, a student at Caltech named <a href="https://en.wikipedia.org/wiki/George_Zweig" rel="nofollow">George Zweig</a> was thinking of something very similar. Zweig (who was at the time visiting <a href="https://home.cern/">CERN</a>) took a mathematically less elaborate approach, observing that the existing particles could be explained as built from three kinds of “aces”, as he called them, with the same properties as Gell-Mann’s quarks.<br /><br />Zweig became a professor at Caltech—and I’ve personally been friends with him for more than 40 years. But he never got as much credit for his aces idea as he should (though in 1977 Feynman <a href="https://arxiv.org/abs/1007.0494">proposed him for a Nobel Prize</a>), and after a few years he left particle physics and started studying the neurobiology of the ear—and now, in his eighties, has started a <a href="https://www.insidermonkey.com/hedge-fund/signition+lp/988/" rel="nofollow">quant hedge fund</a>.<br /><br />Meanwhile, Gell-Mann continued pursuing the theory of quarks, refining his ideas about current algebras. But starting in 1968, there was something new: particle accelerators able to collide high-energy electrons with protons (“<a href="https://en.wikipedia.org/wiki/Deep_inelastic_scattering">deep inelastic scattering</a>”) observed that sometimes the electrons could suffer large deflections. There were lots of details, particularly associated with relativistic kinematics, but in 1969 Feynman proposed his parton (or, as Gell-Mann called it, “put-on”) model, in which the proton contained point-like “parton” particles.<br /><br />It was immediately guessed that partons might be quarks, and within a couple of years this had been established. But the question remained of why the quarks should be confined inside particles such as protons. To avoid some inconsistencies associated with the <a href="https://www.wolframalpha.com/input/?i=exclusion+principle" rel="nofollow">exclusion principle</a>, it had already been suggested that quarks might come in three “colors”. Then in 1973, Gell-Mann and his collaborators suggested that associated with these colors, quarks might have “color charges” analogous to electric charge.<br /><br />Electromagnetism can be thought of as a <a href="https://www.wolframalpha.com/input/?i=gauge+field+theory" rel="nofollow">gauge field theory</a> associated with the Lie group U(1). Now Gell-Mann suggested that there might be a gauge field theory associated with an SU(3) color group (yes, SU(3) again, but a different application than in the eightfold way, etc.). This theory became known as <a href="https://www.wolframalpha.com/input/?i=quantum+chromodynamics" rel="nofollow">quantum chromodynamics</a>, or QCD. And, in analogy to the photon, it involves particles called <a href="https://en.wikipedia.org/wiki/Gluon">gluons</a>.<br /><br />Unlike photons, however, gluons directly interact with each other, leading to a much more complex theory. But in direct analogy to Gell-Mann and Low’s 1954 renormalization group computation for QED, in 1973 the beta function (AKA g times psi function) for QCD was computed, and was found to show the phenomenon of asymptotic freedom—essentially that QCD interactions get progressively weaker at shorter distances.<br /><br />This immediately explained the success of the parton model, but also suggested that if quarks get further apart, the QCD interactions between them get stronger, potentially explaining confinement. (And, yes, this is surely the correct intuition about confinement, although even to this day, there is no formal proof of quark confinement—and <a href="https://www.wolframscience.com/nks/notes-9-16--quantum-field-theory/">I suspect it may have issues of undecidability</a>.)<br /><br />Through much of the 1960s, S-matrix theory had been the dominant approach to particle physics. But it was having trouble, and the discovery of asymptotic freedom in QCD in 1973 brought <a href="https://www.stephenwolfram.com/publications/academic/quantum-chromodynamic-heavy-particle-production.pdf">field theory back to the fore</a>, and, with it, lots of optimism about what might be possible in particle physics.<br /><br />Murray Gell-Mann had had an amazing run. For 20 years he had made a series of bold conjectures about how nature might work—strangeness, V-A theory, SU(3), quarks, QCD—and in each case he had been correct, while others had been wrong. He had had one of the more remarkable records of repeated correct intuition in the whole history of science.<br /><br />He tried to go on. He talked about “grand unification being in the air”, and (along with many other physicists) discussed the possibility that QCD and the theory of weak interactions might be unified in models based on groups like SU(5) and SO(10). He considered <a href="https://www.wolframalpha.com/input/?i=supersymmetry" rel="nofollow">supersymmetry</a>—in which there would be particles that are crosses between things like neutrinos and things like gluons. But quick validations of these theories didn’t work out—though even now it’s still conceivable that some version of them might be correct.<br /><br />But regardless, the mid-1970s were a period of intense activity for particle physics. In 1974, the<br />J/ψ particle was discovered, which turned out to be associated with a fourth kind of quark (<a href="https://www.wolframalpha.com/input/?t=crmtb01&f=ob&i=charm+quark" rel="nofollow">charm quark</a>). In 1978, evidence of a <a href="https://www.wolframalpha.com/input/?i=b+quark" rel="nofollow">fifth quark</a> was seen. Lots was figured out about how QCD works. And a consistent theory of weak interactions emerged that, together with QED and QCD, defined what by the early 1980s had become the modern Standard Model of particle physics that exists today.<br /><br />I myself got <a href="https://www.stephenwolfram.com/publications/early-books/physics-subatomic-particles.pdf">seriously interested in particle physics in 1972</a>, when I was 12 years old. I used to carry around a copy of the little Particle <a href="http://pdg.lbl.gov/2016/html/rpp_archives.html">Properties booklet</a>—and all the various kinds of particles became, in a sense, <a href="https://www.stephenwolfram.com/publications/early-books/introduction-weak-interaction-volume-one.pdf">my personal friends</a>. I knew by heart the <a href="https://www.wolframalpha.com/input/?t=crmtb01&f=ob&i=mass+of+the+the+%5C%5BCapitalLambda%5D" rel="nofollow">mass of the Λ</a>, the <a href="https://www.wolframalpha.com/input/?i=lifetime+of+the+pi0" rel="nofollow">lifetime of the π<sup>0</sup></a>, and a zillion other things about particles. (And, yes, amazingly, I still seem to remember almost all of them—though now they’re all known to much greater accuracy.)<br /><br />At the time, it seemed to me like the most important discoveries ever were being made: fundamental facts about the fundamental particles that exist in our universe. And I think I assumed that before long everyone would know these things, just as people know that there are atoms and protons and electrons.<br /><br />But I’m shocked today that almost nobody has, for example, even heard of muons—even though we’re continually bombarded with them from cosmic rays. Talk about strangeness, or the omega-minus, and one gets blank stares. Quarks more people have heard of, though mostly because of their name, with its various uses for brands, etc.<br /><br />To me it feels a bit tragic. It’s not hard to show Gell-Mann’s <a href="https://twitter.com/stephen_wolfram/status/1134129240377614336" rel="nofollow">eightfold way pictures</a>, and to explain how the particles in them can be made from quarks. It’s at least as easy to explain that there are 6 known types of quarks as to explain about chemical elements or DNA bases. But for some reason—in most countries—all these triumphs of particle physics have never made it into school science curriculums.<br /><br />And as I was writing this piece, I was shocked at how thin the information on “classic” particle physics is on the web. In fact, in trying to recall some of the history, the most extensive discussion I could find was in an <a href="https://www.stephenwolfram.com/publications/early-books/physics-subatomic-particles.pdf" rel="nofollow">unpublished book I myself wrote when I was 12 years old</a>! (Yes, full of charming spelling mistakes, and a few physics mistakes.)<br /><br /><b>The Rest of the Story</b><br /><br />When I first met Murray in 1978, his great run of intuition successes and his time defining almost everything that was important in particle physics was already behind him. I was never quite sure what he spent his time on. I know he traveled a lot, using physics meetings in far-flung places as excuses to absorb local culture and nature. I know he spent significant time with the <a href="https://en.wikipedia.org/wiki/JASON_(advisory_group)">JASON</a> physicists-consult-for-the-military-and-get-paid-well-for-doing-so group. (It was a group that also tried to recruit me in the mid-1980s.) I know he taught classes at Caltech—though he had a reputation for being rather disorganized and unprepared, and I often saw him hurrying to class with giant piles of poorly collated handwritten notes.<br /><br />Quite often I would see him huddled with more junior physicists that he had brought to Caltech with various temporary jobs. Often there were calculations being done on the blackboard, sometimes by Murray. Lots of algebra, usually festooned with tensor indices—with rarely a diagram in sight. What was it about? I think in those days it was most often <a href="https://en.wikipedia.org/wiki/Supergravity">supergravity</a>—a merger of the idea of supersymmetry with an early form of string theory (itself derived from much earlier work on S-matrix theory).<br /><br />This was the time when QCD, quark models and lots of other things that Murray had basically created were at their hottest. Yet Murray chose not to work on them—for example telling me after hearing a talk I gave on QCD that I should work on more worthwhile topics.<br /><br />I’m guessing Murray somehow thought that his amazing run of intuition would continue, and that his new theories would be as successful as his old. But it didn’t work out that way. Though when I would see Murray, he would often tell me of some amazing physics that he was just about to crack, often using elaborate mathematical formalism that I didn’t recognize.<br /><br />By the time I left Caltech in 1983, Murray was spending much of his time in New Mexico, around Santa Fe and Los Alamos—particularly getting involved in what would become the <a href="https://www.santafe.edu/">Santa Fe Institute</a>. In 1984, I was invited to the inaugural workshop discussing what was then called the Rio Grande Institute might do. It was a strange event, at which I was by far the youngest participant. And as chance would have it, in connection with the <a href="https://santafe.edu/research/results/sfi-press/emerging-syntheses-science">republication of the proceedings</a> of that event, I just recently wrote an account of what happened there, which I will soon post.<br /><br />But in any case, Murray was co-chairing the event, and talking about his vision for a great interdisciplinary university, in which people would study things like the relations between physics and archaeology. He talked in grand flourishes about covering the arts and sciences, the simple and the complex, and linking them all together. It didn’t seem very practical to me—and at some point I asked what the Santa Fe Institute would actually concentrate on if it had to make a choice.<br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=1941529720&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>People asked what I would suggest, and I (somewhat reluctantly, because it seemed like everyone had been trying to promote their pet area) suggested “<a href="https://www.stephenwolfram.com/publications/academic/complex-systems-theory.pdf" rel="nofollow">complex systems theory</a>”, and my ideas about the emergence of complexity from things like simple programs. The audio of the event records some respectful exchanges between Murray and me, though more about organizational matters than content. But as it turned out, complex systems theory was indeed what the Santa Fe Institute ended up concentrating on. And Murray himself began to use “complexity” as a label for things he was thinking about.<br /><br />I tried for years (starting when I first worked on such things, in 1981) to explain to Murray about cellular automata, and about my explorations of the computational universe. He would listen politely, and pay lip service to the relevance of computers and experiments with them. But—as I later realized—he never really understood much at all of what I was talking about.<br /><br />By the late 1980s, I saw Murray only very rarely. I heard, though, that through an agent I know, Murray had got a big advance to write a book. Murray always found writing painful, and before long I heard that the book had gone through multiple editors (and publishers), and that Murray thought it responsible for a heart attack he had. I had hoped that the book would be an autobiography, though I suspected that Murray might not have the introspection to produce that. (Several years later, a <em>New York Times</em> writer named George Johnson wrote what I considered a <a href="https://www.amazon.com/Strange-Beauty-Gell-Mann-Revolution-Twentieth-Century/dp/0679756884?tag=lubosmotlsref-20">very good biography of Murray</a>, which Murray hated.)<br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=0805072535&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>But then I heard that Murray’s book was actually going to be about his theory of complexity, whatever that might be. A few years went by, and, eventually, in 1994, to rather modest fanfare, Murray’s book <a href="https://www.amazon.com/Quark-Jaguar-Adventures-Simple-Complex/dp/0805072535/?tag=lubosmotlsref-20"><em>The Quark and the Jaguar</em></a> appeared. Looking through it, though, it didn’t seem to contain anything concrete that could be considered a theory of complexity. George Zweig told me he’d heard that Murray had left people like me and him out of the index to the book, so we’d have to read the whole book if we wanted to find out what he said about us.<br /><br />At the time, I didn’t bother. But just now, in writing this piece, I was curious to find out what, if anything, Murray actually did say about me. In the printed book, the index goes straight from “Winos” to Woolfenden. But online I can find that there I am, on page 77 (and, bizarrely, I’m also in the online index): “As Stephen Wolfram has emphasized, [a theory] is a compressed package of information, applicable to many cases”. Yes, that’s true, but is that really all Murray got out of everything I told him? (George Zweig, by the way, isn’t mentioned in the book at all.)<br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=1579550088&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>In 2002, I’d finally finished my own decade-long basic science project, and I was getting ready to publish my book <a href="https://www.wolframscience.com/nks/"><em>A New Kind of Science</em></a>. In recognition of his early support, I’d <a href="https://www.wolframscience.com/nks/pxiii--preface/" rel="nofollow">mentioned Murray</a> in my long list of acknowledgements in the book, and I thought I’d reach out to him and see if he’d like to write a back-cover blurb. (In the end, <a href="https://blog.stephenwolfram.com/2011/10/steve-jobs-a-few-memories/">Steve Jobs</a> convinced me not to have any back-cover blurbs: “Isaac Newton didn’t have blurbs on the <em>Principia</em>; nor should you on your book”.)<br /><br />Murray responded politely: “It is exciting to know that your magnum opus, reflecting so much thought, research, and writing, will finally appear. I should, of course, be delighted to receive the book and peruse it, and I might be able to come up with an endorsement, especially since I expect to be impressed”. But he said, “I find it difficult to write things under any conditions, as you probably know”.<br /><br />I sent Murray the book, and soon thereafter was on the phone with him. It was a strange and contentious conversation. Murray was obviously uncomfortable. I was asking him about what he thought complexity was. He said it was “like a child learning a language”. I asked what that meant. We went back and forth talking about languages. I had the distinct sense that Murray thought he could somehow blind me with facts I didn’t know. But—perhaps unfortunately for the conversation—even though <em>A New Kind of Science</em> doesn’t discuss languages much, my long efforts in computational language design had made me quite knowledgeable about the topic, and in the conversation I made it quite clear that I wasn’t convinced about what Murray had to say.<br /><br />Murray followed up with an email: “It was good to talk with you. I found the exchange of ideas very interesting. We seem to have been thinking about many of the same things over the last few years, and apparently we agree on some of them and have quite divergent views on others”. He talked about the book, saying that “Obviously, I can’t, in a brief perusal, come to any deep conclusions about such an impressive tome. It is clear, however, that there are many ideas in it with which, if I understand them correctly, I disagree”.<br /><br />Then he continued: “Also, my own work of the last decade or so is not mentioned anywhere, even though that work includes discussions of the meaning and significance of simplicity and complexity, the role of decoherent histories in the understanding of quantum mechanics, and other topics that play important roles in <em>A New Kind of Science</em>”. (Actually, I don’t think I discussed anything relevant to decoherent histories in quantum mechanics.) He explained that he didn’t want to write a blurb, and ended: “I’m sorry, and I hope that this matter does not present any threat to our friendship, which I hold dear”.<br /><br />As it turned out, I never talked to Murray about science again. The last time I saw Murray was in 2012 at a peculiar event in New York City for promising high-school students. I said hello. Murray looked blank. I said my name, and held up my name tag. “Do I know you?”, he said. I repeated my name. Still blank. I couldn’t tell if it was a problem of age—or a repeat of the story of the beta function. But, with regret, I walked away.<br /><br />I have often used Murray as an example of the challenges of managing the arc of a great career. From his twenties to his forties, Murray had the golden touch. His particular way of thinking had success after success, and in many ways, he defined physics for a generation. But by the time I knew him, the easy successes were over. Perhaps it was Murray; more likely, it was just that the easy pickings from his approach were now gone.<br /><br />I think Murray always wanted to be respected as a scholar and statesman of science—and beyond. But—to his chagrin—he kept on putting himself in situations that played to his weaknesses. He tried to lead people, but usually ended up annoying them. He tried to become a literary-style author, but his perfectionism and insecurity got in the way. He tried to do important work in new fields, but ended up finding that his particular methods didn’t work there. To me, it felt in many ways tragic. He so wanted to succeed as he had before, but he never found a way to do it—and always bore the burden of his early success.<br /><br />Still, with all his complexities, I am pleased to have known Murray. And though Murray is now gone, the physics he discovered will live on, defining an important chapter in the quest for our understanding of the fundamental structure of our universe.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-48288240058581961582019-05-31T07:33:00.001+02:002019-05-31T18:24:32.394+02:00Dijkgraaf and Witten on math and physicsTwo days ago, the director of the Institute for Advanced Physics (IAS) Robbert Dijkgraaf decided to go on the media offensive. For decades, folks like him have found it OK to simply ignore the eukaryotes who pumped dumb anti-physics delusions through almost all the media. Suddenly, it's seen that a process was taking place, after all, and it may be good to counter it.<br /><br /><iframe width="407" height="277" src="https://www.youtube.com/embed/RjthuCDzAnY" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe><br /><br /><em>Dijkgraaf and Witten on math vs physics, 22 minutes</em><br /><br />On May 29th, the IAS used the opportunity of the publication of a new book by Graham Farmelo, "<em>The Universe Speaks in Numbers</em>", to organize a mini-conference about the relationships between mathematics and physics. Talks by the first female winner of the Abel Prize for mathematics Karen Uhlenbeck, by Freeman Dyson, Nima Arkani-Hamed, Farmelo, Dijkgraaf, Kyle Cranmer, Thomas Lam, Greg Moore, Natalie Wolchover and a few others may be found on the <a href="https://www.youtube.com/user/videosfromIAS/videos">IAS YouTube channel</a>.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />The director himself also decided to record a conversation that would become the most watched YouTube video ever (see above). He chose an employee as his talking buddy carefully – it was Edward Witten – and indeed, the video is already approaching 1,000 views, close to 6.2 billion earned by a <a href="https://www.youtube.com/watch?v=kJQP7kiw5Fk" rel="nofollow">Despacito video</a>. ;-)<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />At the beginning, Dijkgraaf shyly tries to persuade the viewers that Witten is qualified to speak about mathematics and physics. Robbert checked that no one is throwing tomatoes at them because of this potentially blasphemous statement. <br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=0465056652&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>Fine. Witten says that the gap between math and physics isn't due to personalities but really due to the different logic and motivation of both fields. The gap grew for 25 years after the Second World War, largely because physics was being advanced by looking at rather dirty experiments that mathematicians don't like – and also because quantum field theory became the main theoretical foundation of physics.<br /><br />Mathematicians have had trouble to develop a rigorous foundation of e.g. \(D=4\) quantum field theories – QFTs are simply too mathematically hard for mathematicians, a major example of a framework where the physicists' relaxed attitude to rigor and the theoretical physicists' somewhat higher intelligence relatively to the mathematicians leads to consequences. In fact, almost no one seems to be working on the axiomatic foundations of QFTs today. Dijkgraaf tried to persuade Witten to repeat many of Dijkgraaf's opinions about the future of thinking or about the conceptual scheme of all the knowledge but you may see that in almost all cases, Witten was very careful and at least ambiguous about any potential agreement with Dijkgraaf.<br /><br />For example, Dijkgraaf thinks that quantum field theory is ill-understood — the cooperation between the patchy partial understanding looks too chaotic to him – and we will discover some completely new or "more global" understanding of quantum field theories in the future. Well, it's possible but like Witten who politely stayed silent, I am skeptical when it comes to such far-reaching statements. I would personally bet that quantum field theory won't undergo new huge revolutions in the way how we define it – that it is "more than 50%" settled subject when it comes to its foundations. And if the network of relationships between various QFT ideas looks chaotic to Dijkgraaf, it's his psychological problem but this network is probably here to stay.<br /><br />This view of Dijkgraaf is one of the "politically correct" views that are promoted in the string-theory-friendly but otherwise pop science mainstream media. It's probably not a coincidence that a chap who is aligned with these views has become a director of the research-only institute where Einstein has worked for a long time. I may have shared Robbert's intuition at some point but I think that I have largely moved on – and it seems that so did Witten and others. In particular, I can't imagine how the complex and diverse "perspectives" on QFTs and their properties could ever be "undone" or replaced with something totally different – except if the change may be described as a disappearing knowledge or a symptom of a dumbed down mankind. In other words, I feel that by his seemingly innocent comments directed against the "untamed complexity of insights in QFT", Dijkgraaf sounds like a "Smolin Lite" and this attitude is still "Wrong Lite" – and a manifestation of some math-phobia if not knowledge-phobia. Certain complicated insights are here with us to stay. Sorry, Robbert. They could disappear if physicists stopped doing physics and started to say "OM" (or some equation-free would-be philosophical clichés, like the clichés popular among the eukaryotes) which is simpler and "less messy" – but it's also less physics, unless you add at least some equations of (the noncommutative) OM-theory.<br /><br />OK, so I am obviously with Witten on these questions. My reason is that QFT really looks transparent enough. Mathematicians don't know how to rigorously treat path integrals and renormalization but physicists, at their level of rigor, do know how to deal with these things and QFT still "is" some theory described by explicitly constructed degrees of freedom on an explicitly real spacetime. This theory leads to Green's functions and other observables that exhibit patterns (like the patterns of some QFTs explained by the associahedrons etc.) and new patterns may be found in the future. But those are really aspects of the "solutions", not a part of the definition. General QFTs are probably going to be defined in ways that just cosmetically differ from the present ones. A limit of a lattice QFT or whatever. There's no room for genuine new mystery – which may only hide in quantum gravity which we currently <em>can't</em> fully define in terms of explicit degrees of freedom living on an explicit spacetime now.<br /><br />Since the 1970s or so, Witten implicitly said, mathematics and physics got closer again – because the power of experiments to make quick changes had been largely depleted and because string theory and perhaps a few analogous developments were expanding and they're clearly close to be a common topic exciting both physicists and mathematicians. But this drift shouldn't be overstated, there's still a gulf in between math and physics.<br /><br />Robbert asked Ed about Ed's predictions that were made or could have been made 30 years ago. Witten had expected a more unifying definition of the laws of string theory to be found. It really wasn't. Instead, most of the progress took place in the second part of the research which isn't the "search for the very laws of physics", namely in "the research into the solutions of the theory". In particular, the strongly coupled regime of string/M-theory was largely understood much more than before the mid 1990s – but surprisingly enough, this understanding was achieved without a huge progress in the "writing of the basic laws".<br /><br />After 11:11, you see another theme where the two men aren't quite on the same frequency and I'm closer to Witten again. Dijkgraaf is convinced that the geometry must be shown to be emergent or an "afterthought". Well, I used to say similar things but I switched to thinking that <em>some</em> geometry must be "totally and fully present" in any formulation of a theory that is in any way equivalent to string theory (or QFT) as we know it today. You may be very free to choose the background geometry that is the starting point to organize the Hilbert space and observables (T-duality, mirror symmetry, string-string duality, AdS/CFT, ER=EPR, and other generalized dualities guarantee lots of freedom) but you shouldn't choose "no geometry" because "no geometry means no physics". <br /><br />So I think some geometry will always exist in the initial form of the laws of physics – and the new progress may be "what kind of degrees of freedom" may be associated with the geometry and why various choices are really physically equivalent to each other. Strings, bilocal wormholes etc. have been added to generalize the point-like particles in QFTs. Ironically, the BFSS Matrix theory seems "most distant" from what I say. But it still has the spatial coordinates of the D0-branes in it etc. The spacetime isn't eliminated. Just the second quantization from QFT is replaced with the wave functions for block-diagonal matrices.<br /><br />Dijkgraaf forced Witten to pick some high points – links between math and physics that have excited Witten. Witten picked some technical answers.<br /><br />Also, Dijkgraaf later said that string theory has helped to bring different subdisciplines of mathematics closer to each other and that much of the separation of mathematics into subbranches is an artificial, sociological effect, not a reflection of true long-term borders in the realm of mathematics. I think that I completely agree with Dijkgraaf on this one. And so does Witten, it seems. When asked "why it's so", Witten said that "it's because the Universe was created by a mathematician". Laughter.<br /><br />Steve Shenker has discovered the Shenker-Murphy law that says that "you always avoid one type of mathematics and it's the mathematics that will be relevant for your next paper". So Dijkgraaf obviously wanted to know which part of mathematics Witten is avoiding LOL.<br /><br />To address this funny question, Witten mentioned that he always found the number theory – and the arithmetic Langlands program – to be too abstract which is why he chose the geometric Langlands program which could be advanced in his lifetime. (Witten kept on pushing his campaign to persuade everyone that he's primarily a full-blown physicist whose heart is full of blood and milk, not a damn mathematician.) He believes that number theory may become important in the physics-like thinking in the distant future – and he is therefore jealous about the future generations. These guesses look so sensible to me...<br /><br />At the end, since 18:00, Witten was asked a big question and answered that he found it extremely likely that physics was on the right track and he considered it implausible that string theory (that addresses so many physics questions and that works at this demanding enough level, and that also sheds so much light on mathematics) could be just a series of coincidences that ultimately have nothing to do with the Universe. I completely share this intuition. Witten admits that this kind of thinking may be considered as "not being scientific evidence".<br /><br />Dijkgraaf said that we would never get rid of string theory because it's already a part of QFT that has been proved essential to understand the Universe etc. Witten agreed but saw Dijkgraaf's comment as some kind of "a partial surrender" or an attack on the primary purpose of string theory, i.e. to be a "theory of everything". So Witten authoritatively and importantly said that string theorists shouldn't forget that the real primary – and still totally viable – goal was to find the correct vacuum that describes all the observed phenomena.<br /><br />String theory is primarily our successful framework unifying all the known forces and all types of physical objects and phenomena – and the process of completely proving and settling this statement is still ongoing. I feel that Dijkgraaf might be among those who have agreed with the eukaryotes to classify this <em>absolutely essential</em> point as being politically incorrect. And if I am right, it's just too bad when a director of a crucial institute is being manipulated by the lowly life forms in this way.<br /><br />"If string theory is not right, who is living in the Universe inhabited by string theory? ;-)" It is a quote that Dijkgraaf attributed to Witten. Witten said that it couldn't all be a coincidence as a response to this quote.<br /><br /><hr><b>Wolfram and Gell-Mann</b><br /><br />If you have the lust and nerves for very insightful, informative, Wolfram-centric, and tense <a href="https://blog.stephenwolfram.com/2019/05/remembering-murray-gell-mann-1929-2019-inventor-of-quarks/">memories of Murray Gell-Mann as remembered by Stephen Wolfram</a>, click at the link.<br /><br />They've known each other very well – Wolfram has spent years at Caltech as an ingeniuous kid-particle physicist. Wolfram claims credit for some things associated with Gell-Mann, e.g. for marketing the Santa Fe Institute as a "complexity" institute. In 2012, <a href="https://motls.blogspot.com/2019/05/murray-gell-mann-1929-2019.html?m=1">Gell-Mann</a> no longer recognized Wolfram. I guess that the evolving appearance of the latter was the main reason. Wolfram also says things I couldn't agree with – like some mysterious words about "muon's not being understood" (muon is as understood as the electron – they really <em>are</em> completely analogous and only differ by the mass which also implies muon's instability), his implicit denial of the importance of quantum mechanics (and, somewhat smaller, importance of Gell-Mann–Hartle consistent histories), his idea that the cellular automatons are very important, and more. <br /><br />The text makes it clear that Gell-Mann has wanted to influence the world at many levels – well, just like Wolfram himself, I would add – but it hasn't quite worked out. It's bad it didn't. I do think that a guy like Gell-Mann who spoke 13 languages should influence the environments where languages are considered important, for example. Also, there's a fun idea involving birds that Wolfram suggested – or at least the idea emerged in my skull after I read Wolfram's memories. Feynman used to pick "<a href="https://www.youtube.com/watch?v=lFIYKmos3-s">names of birds</a>" as something that he was taught by his father to be useless. This story could have been "improved" by Feynman and Feynman could have deliberately chosen birds because Gell-Mann was a keen ornithologist or birdwatcher! The bird name story of Feynman's could have been an attack on Gell-Mann, too! ;-)Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-5728243100079824432019-05-25T12:21:00.000+02:002019-05-26T13:55:48.564+02:00Murray Gell-Mann: 1929-2019Sadly, as reported by <a href="https://www.nytimes.com/2019/05/24/obituaries/murray-gell-mann-died-.html">The New York Times</a> and many <a href="https://news.google.com/stories/CAAqSQgKIkNDQklTTERvSmMzUnZjbmt0TXpZd1NoOGFIV1JOYnpWVmJuSkpkR05xZFcxb1RYWjJWMU5mY1VacU56TmFhVzVOS0FBUAE?q=gell-mann&lr=English&hl=en-US&gl=US&ceid=US:en" rel="nofollow">others</a>, <a href="https://en.wikipedia.org/wiki/Murray_Gell-Mann">Murray Gell-Mann</a> died at home yesterday, May 24th, at age of 89.7. He was clearly one of the greatest living physicists – by integrated achievements. It was cancer that killed him – for years, he's used his broad scientific expertise to defeat that lethal process inside his body. See <a href="https://www.youtube.com/watch?v=gXwJLSY_HFQ">this talk by Gell-Mann and David Agus</a> about cancer. Physician Agus considered Gell-Mann to be <a href="https://twitter.com/DavidAgus/status/1131991553822449669?ref_src=twsrc%5Egoogle%7Ctwcamp%5Enews%7Ctwgr%5Etweet">his mentor</a>. Cancer has also killed Gell-Mann's first beloved wife.<br /><br /><img src="https://lh3.googleusercontent.com/Titj9yEyFHNQx-TUu5r15B0JRdt2UsuPdAKtFwRhBUI0S8RP23cVZpaNvgr0KPX77fzyeCIuQWsB7CWE5-tb0ETBnpgZaFqovEKdNMA5jpqyOfDxDWL-kVTbAsqpP-NKHG45FgdiNpk9QN7StqT9ztHB4PNHbynpwqrVdKNttLFTEzCCYrGdiV4BiSZ9D0E9c9bu8lZ-jrctyi2F4vQYUNM670TWcbWZyPjFJe0_v4FanYkB8WeiURUG0CFN8E75nua9VgWwB2mMg5aGXRE14yTuJv4-cQ3Eu0GuSpXaWQ0X9oFaj2BrFyb5E-9NmOqHQVSc7ijfbjn4yfMrQ2sdC2Ak0eZDTNp1qejvkKc7lWStjl_ecxn0ILAwDxhzOfY8kS-0AKtgY5II0ooae6MgFkjk9yb9ZLCRSQ7RiHXvqD60aD3T-qzYQxLDXRmPgzOSSeOI8I4SbYd50mJoEZ9vHfjGb3lEUFqrHDuPxyYyjlXxXMq8BD-O-axI4NZgVp3WvFQnBo1fV0thTq784LK1_YuJ-3okUKlRS6_YhUs-gxTHm4Ij83Z3V9kpTraImyjBaOxdLms2SNIuX6_nlioV0ZCc7usUEeoZAD1frRrXgpX_SZ1XBOGJMNUU6DJ5UFu4XnaFrj3W_hcfmYVAGgY-n06iwbyHvbb3bFEkdhTIz6vOuoOehX-sTmhRTrkERTVxniuVPwDpuYZwnKeqkz6YEJ6u=w640-h480-no" width=407><br /><br /><em>A picture of MGM and Thomas Appelquist that I took in Harvard's Science Center in 2005. If you think that you are a theoretical physicist but I haven't photographed you, then you effectively fail to exist.</em><br /><br />He was born in Manhattan in 1929 to a Jewish family that arrived from the present Ukrainian territory – then a town named Černovice (close enough to Czechoslovakia so we have our name!) in our beloved homeland of Austria-Hungary. <br /><br />He got his PhD when he was 21. His students included Ken Wilson (Gell-Mann really helped the renormalization group ideas to emerge, think about the Gell-Mann–Low equations), Sidney Coleman (who was celebrated at the event where I met Gell-Mann), Jim Hartle (that's linked to Gell-Mann's interest in foundations of QM – they were also among the people who authored the consistent histories), and Barton Zwiebach (a top expert in string <em>field</em> theory today, I discuss Gell-Mann and strings later). Gell-Mann has also discovered the seesaw mechanism that might give neutrinos their masses of the right magnitude.<br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=0805072535&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>Gell-Mann received his 1969 Nobel prize in physics mainly for the 1964 theoretical discovery of quarks (independently of George Zweig) – more precisely, as Ed S. insists, he got the prize for the <a href="https://en.wikipedia.org/wiki/Eightfold_way_(physics)">Eightfold Way</a> which only "led" to quarks – which made the classification of hadrons (proton, neutron, and their cousins) meaningful. Gell-Mann copied the name "quark" from Finnegans Wake by James Joyce ("Three quarks for Muster Mark" – indeed, it's not "Mister Clark" as I wanted to write LOL). That fancy choice was an early example of his deep interest in linguistics (he was claimed to speak 13 languages fluently, wow). <br /><br />He was also obsessed with birdwatching or ornithology, archaeology, and more conventional intellectual interests. He possessed three houses in different U.S. states (Santa Fe, Aspen, Pasadena in NM,CO,CA), one of them was a "museum", and he loved-and-knew expensive wine and cars (guess where the "Jaguar" comes from in "Quark and the Jaguar" – the animal was there just to mask that he wanted to brag about the car).<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=0738202991&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>Gell-Mann also stole the term "Eightfold Way" from the Eastern religions to describe some \(SU(3)\) octets and then he was surprised that many people thought that particle physics had something to do with Eastern religions. He has clearly done more fundamental work involving \(SU(3)\) in physics (especially the flavor symmetry) than any other physicist – which is also why the \(SU(3)\) counterparts of \(SU(2)\) Pauli matrices are called the Gell-Mann matrices.<br /><br /><a href="http://inspirehep.net/search?ln=en&ln=en&p=find+a+gell-mann%2Cm&of=hcs&action_search=Search&sf=&so=d&rm=&rg=25&sc=0">Inspire</a> shows that he has written 9 renowned papers – which are dominated by the strong force but actually include the electromagnetic and the weak force papers, too. (The weak force paper is the famous Feynman—Gell-Mann FG paper that isn't FG, i.e. fully good.)<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Gell-Mann was a collaborator and a well-known rival of Feynman at Caltech. Gell-Mann represented the approach that wants to be "more conventional or aligned with the community" while Feynman was the "maverick". <br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=B010SEM6WC&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>Gell-Mann has had one adopted child and two biological children, Lisa and Nick. Those have had a strained relationship with their dad. In particular, instead of being inspired to do some intelligent stuff, Lisa – previously a dutiful child – was <a href="https://books.google.com/books?id=VNSNkphp4HoC&pg=PA419&lpg=PA419&dq=lisa+gell-mann+marxism&source=bl&ots=WPy0FfqsSW&sig=ACfU3U17PY-11pXTJ6Qo5g7W8WuCsudczw&hl=cs&sa=X&ved=2ahUKEwjJjYzr7rbiAhWRY1AKHf9MDCgQ6AEwAXoECAgQAQ#v=onepage&q=lisa%20gell-mann%20marxism&f=false" rel="nofollow">suck into extreme left-wing politics</a> – the Central U.S. Organization for Marxism-Leninism – by an incredibly hypocritical rich man from a New York neighborhood. So I guess that he didn't like the left-wing bastards who have basically destroyed his daughter.<br /><br />I have spoken to Gell-Mann for half an hour during the 2005 Sidneyfest (celebration of Coleman's life). He was a captivating storyteller and he was excited that I was interested in Feynman's opposition to toothrbrushes – Gell-Mann really thought that Feynman's teeth were decaying and he was doing really stupid things for his maverick status – and in Gell-Mann's role in a <a href="https://www.youtube.com/watch?v=XZ8XM7JVpYw" rel="nofollow">wonderful TV commercial for Enron</a> (for younger readers: Enron was something like Tesla but 20 years ago).<br /><br />While Feynman loved to mock John Schwarz in the elevators of Caltech ("How many dimensions does your world have today, John?"), Gell-Mann was a key sponsor and defender who has allowed an early string theory group to emerge at Caltech. In the early 1970s, Gell-Mann was just capable of figuring out that string theory was likely to be here with us to stay – as the default state-of-the-art foundation of all of physics – at least for 50 more years. Barton Zwiebach's years as Gell-Mann's student say something, too.<br /><br />But just to be sure, Gell-Mann didn't understand the value of string theory right away. As recently as in 1970, he mocked Lenny Susskind for strings, too – and he played some role in the delaying of Susskind's paper.<br /><br />The difference between Feynman's and Gell-Mann's attitude to string theory had a very simple primary reason. As <a href="https://www.youtube.com/watch?v=zWLYlyHj9ys">this 3-minute monologue</a> by Gell-Mann shows, Gell-Mann actually understood string theory at a level that was about 50 times more detailed and technical than Feynman's (Gell-Mann knew something that no critic does, namely the structure of actual papers, such as those about sectors in the superstring). So Feynman did talk as an absolute layman, Gell-Mann did not. Every person in the world who says negative things about string theory is really a layman. In <a href="https://www.youtube.com/watch?v=uWtb4NIQtJA">this 2-minute monologue</a>, Gell-Mann complained that it was a pity that Shelly Glashow became the original hostile promoter of the fundamental misconceptions about "string theory that couldn't be tested" etc. More on <a href="https://www.youtube.com/results?search_query=gell-mann+string">Gell-Mann and strings</a>, also in his <a href="https://books.google.com/books?id=WNZyoUteXIkC&pg=PA129&lpg=PA129&dq=%22Note+on+the+prehistory+of+string+theory%22&source=bl&ots=VecHh6rIxu&sig=ACfU3U2tQ4NEf44byv5TDVL9QXrXk3QGRg&hl=cs&sa=X&ved=2ahUKEwj0l_POkLniAhUDa1AKHdNDAYcQ6AEwBHoECAkQAQ#v=onepage&q=%22Note%20on%20the%20prehistory%20of%20string%20theory%22&f=false" rel="nofollow">Note on Prehistory of String Theory</a> (making Gell-Mann's connections to early stringy technical results clear).<br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=1580895409&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe><em>This book is an introduction to the quark theory for 1-year-old students.</em><br /><br />Aside from his support for string theory, Gell-Mann is also one of the forefathers of naturalness – he coined the totalitarian principle which states that everything that is not forbidden is mandatory (just like in the totalitarian regimes). In particle physics, it means that all coefficients that can't be proven to be zero by some principles are bound to be nonzero and probably "of order one" in some units. He has also opposed "quantum flapdoodle", the misuse of quantum mechanics' alleged weirdness designed to push other topics in strange directions.<br /><br />Gell-Mann's name has appeared in <a href="https://motls.blogspot.com/search?q=Gell-Mann&m=1&by-date=true">103 TRF blog posts</a>. You may want to read some of them. Try a <a href="https://www.google.com/search?num=100&hl=en&rlz=1C1GGLS_en___CZ311&q=site:motls.blogspot.com+gell-mann&btnG=Search" rel="nofollow">Google ordering</a> by relevance.<br /><br />RIP, Murray.<br /><br /><hr>P.S.: If you want to share my frustration about how much the BBC's and other popular science programs have dumbed down in recent 50 years, watch <a href="https://www.youtube.com/watch?v=BGeW6Nc6IMQ&list=PL02D595043A13CC8A">Strangeness Minus Three</a> from 1964 (three parts featuring both Feynman and Gell-Mann; and Yuval Ne'eman, too). One part of the gloomy evolution is that journalists have generally turned into a cesspool. Another cause of the evolution is that the scientists have lost the spine and self-confidence to insist that they determine what is actually being said about science. The body of scientists have been turned into a obedient herd of effeminate tools.<br /><br /><hr><br />Here you have another, 12-minute-long monologue about the birth of the quark model (thanks, Willie!):<br /><br /><iframe width="407" height="277" src="https://www.youtube.com/embed/KDkaMuN0DA0" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe><br /><br />He ordered the hadrons into multiplets, thought about subunits, and found out that they – the quarks – had to have fractional charges \(+2/3\) and \(-1/3\). With a napkin during a visit, he realized that this counterintuitive trait wouldn't be a problem as long as the quarks stayed confined (it was almost a decade before the confinement was derived from QCD). He called the quarks "mathematical" because they had to be "confined". Many historians later wrote that the word "mathematical" meant that he didn't believe the quarks at all which is completely wrong!<br /><br />While the Nobel foundation didn't make that mistake, the fabricated confusion was a reason why the prize wasn't given to him easily and simply "for the quarks", as dictated at the top. That's obviously what should have taken place.<br /><br />These days this position is even more widespread – various overgrown clones of the critics of physics that emerged in recent 15 years use the word "mathematical" as if it were something wrong – and they completely contaminate the journalistic environment surrounding physics with these toxic delusions. But there is absolutely nothing wrong about it – quarks are just inseparable from each other. The quark theory turned out to be perfectly correct – the quarks were just not directly observable in isolation which doesn't contradict the fact that they're demonstrably and completely real. The case of string theory is so far perfectly analogous. It's also "mathematical" but it doesn't mean that there is anything "physically unreal" about it! Clearly, all the incompetent people have failed to understand that mathematics must play and has played a decisive role in physics since the very "Newtonian" beginnings – they're still dreaming about a setup in which mathematics is suppressed, declared to be either wrong or not even wrong, and decisions are made by some sociological tools or bullying.<br /><br />Gell-Mann has repeatedly tried to talk to the historians who write the untruths that were frustrating to him and fix their perverted story about the history but it was like talking to the wall. Also, Gell-Mann said that he had the sound approximating "cork" before he found the final spelling "quark" in Joyce's book. I think that if this chronology is authentic, it was quite some good luck that Joyce wrote about quarks – and in fact, there were three quarks in the sentence!Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-14614232858483952262019-05-20T11:42:00.001+02:002019-05-20T11:56:03.316+02:00WGC and modular invariance: does the WGC constrain low-energy physics at all?Physicists writing papers about the Weak Gravity Conjecture (WGC) seem to be particularly excited about their work so they often submit their paper to be at the top of the hep-th list. Two weeks ago, a paper on the <a href="https://motls.blogspot.com/2019/05/axion-weak-gravity-conjecture-passes.html?m=1">axion WGC</a> was posted one second after the collection of papers for the new day started. <br /><br />That's exactly what was achieved by another group of authors, Shiu and Cole at Amsterdam and Aalsma in Madison, who just submitted<br /><blockquote><a href="https://arxiv.org/abs/1905.06956">Weak Gravity Conjecture, Black Hole Entropy, and Modular Invariance</a><br /></blockquote>a second after the beginning of the new arXiv day. A funny achievement of this paper is that it is the 500th followup of the <a href="http://inspirehep.net/search?ln=en&p=find+a+vafa+and+a+motl&f=&action_search=Search">WGC paper</a> according to Inspire, so the Weak Gravity Conjecture has made it to the highest, "renowned", category of papers. Both Arkani-Hamed and Vafa have 19 renowned papers so there is no reason to congratulate them, and Alberto has 2+1 renowned papers with Nima et al. But it's my first renowned paper, so congratulations to me. ;-)<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />One followup is needed for our 7-author <em>pp</em>-wave paper to join the Screwing String Theory as a famous paper (250+) and one or two dozens are needed for the two quasinormal papers to do the same.<br /><br />In a recent discussion, commenter nicknamed TwoBs has suggested that the WGC and perhaps similar swampland criteria are (almost?) vacuous because low-energy considerations along with the <em>mere fact</em> that the low-energy effective theory is an RG limit of a more fundamental theory at high energies is enough to prove that e.g. gravity is the weakest force and similar inequalities.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />In particular, the WGC says that there exist elementary particles whose charge-to-mass ratio exceeds the ratio calculated for extremal black holes. That's enough for a weak form of WGC – it's enough for large extremal black holes to be able to evaporate although their "right to do so" is on the edge. And TwoBs has pointed out that one may basically show that some higher-derivative corrections to the black holes' charge-to-mass ratio is guaranteed to have the right sign required by the WGC.<br /><br />At this level, I would agree that the WGC is basically "proven" because the slightly "superextremal" black holes may be counted as objects that are predicted by the WGC to exist.<br /><br />Well, Aalsma et al. – the authors of the new paper – disagree with this view of TwoBs. Instead, they say that these large "superextremal" black holes whose existence may be proven just from some low-energy effective field theory <em>cannot be considered elementary particles</em> because their mass is too high and the effective theory where they're treated as elementary particles is no longer valid at the high energies comparable to these black holes' mass.<br /><br />I am not sure where I stand on this subtle debate. Of course, we weren't terribly rigorous about our statement. But I think that what we wrote was that there exist some objects with the "superextremal" charge-to-mass ratio and the black holes that are heavier than the Planck mass – and those are the microstates whose charge-to-mass ratio only depends on the low-energy effective field theory, in some expansion – are enough to satisfy the WGC. We didn't require these states to be very light.<br /><br />In fact, it's very likely that if the heavy black holes that are "superextremal" according to the charge-to-mass ratio exist, there must also exist "rather light" ones whose mass is at most of the order of the Planck mass because it's not clear where the extra "parameteric" enhancement of the minimum black hole mass that obeys the WGC could come from.<br /><br />At any rate, Aalsma et al. at least think that we <em>should</em> have formulated a stronger version of the conjecture that basically says that the elementary particles with the "superextremal" charge-to-mass ratio should also exist at masses that are <em>lower</em> than the Planck mass, or at least <em>lower than or comparable</em> to the Planck mass. After all, the probability that a large black hole Hawking emits another "rather large" black hole is exponentially tiny and maybe we don't want the "loophole" to be this shaky.<br /><br />And once we strengthen the WGC in this way, i.e. once we require the "superextremal" sub-Planckian particles, the low-energy arguments <em>no longer</em> guarantee the existence of such states. I am not aware of terribly strong arguments that would say that we <em>should</em> strengthen the WGC in this way. But to be sure, this strengthening must be considered important for the paper by Aalsma et al. to be important, too! ;-)<br /><br />OK, so Aalsma et al. implicitly say that all of us <em>should</em> strengthen the WGC and the states with the "superextremal" charge-to-mass ratio should be sub-Planckian. Can we say something about the existence of these light particles that guarantee the WGC in that case? To justify their "Yes" answer, they use a paradigm that all of us have <em>always wanted</em> to be relevant for the swampland arguments, namely the UV-IR connection.<br /><br />The laws apparent at high energies (UV, ultraviolet region) – like the detailed patterns of the heavy black hole microstates – are being linked to the laws seen at low energies (IR, infrared region). While banned in the effective field theories, pretty much by their definition, the UV-IR connections are <em>believed</em> to be omnipresent in string/M-theory. But there really exists a subclass of these connections that is understood well – the modular invariance of perturbative string theory.<br /><br />When the string coupling constant \(g_s\ll 1\) is very small, string theory may be well described by the actual old-fashioned version of string theory with world sheets of a well-defined low-genus topology. The one-loop topology for closed-string diagrams is the torus which is a rectangle with the periodic identification of the top-and-bottom sides and the left-and-right sides, like in Pacman.<br /><br /><img src="https://1.bp.blogspot.com/-ZHOy7UxFJh4/USf6K9wD9rI/AAAAAAAABDY/d5L4GKQQhTU/s1600/Pac1.png" width=407><br /><br /><em>This only has the left-right identification.</em><br /><br />A funny fact is that a rectangle may be rotated by 90 degrees. So you may consider the vertical dimension of the torus to be the Euclidean time in the thermal partition sum (expressed as a path integral); or the horizontal one (or infinitely many other, tilted direction, but let's not go there). And the invariance of the toroidal path integral under the rotation by 90 degrees may be interpreted as an identity relating two seemingly different partition sums. This equality is known as the modular invariance. <br /><br />When one of the rectangles is "short and wide", the other one is "tall and thin". In the language of temperatures, it means that when one partition sum is dominated by low-mass string states, relatively to the string scale, the other one is dominated by high-mass string states. It means that the distribution of the low-string vibration states isn't really independent from the distribution of the high-string vibration states. And in a heterotic string case, Aalsma et al. calculate the masses as calculable functions of \(\alpha'\), the inverse string tension, and decide that it's really enough to strengthen the WGC. <br /><br />Due to a calculation involving the toroidal world sheets, the weak form of the WGC which may be justified by purely low-energy effective field theory arguments – the existence of some mildly "superextremal" black holes – may be strengthened to the strong form of the WGC – the existence of low-lying string excitations that are "superextremal" by their charge-to-mass ratio. The strengthening itself requires characteristically stringy identities, those resulting from the modular invariance.<br /><br />It's very interesting but I think that the very question whether the WGC and swampland conditions "really depend" on some characteristically stringy properties of quantum gravity will not quite be settled by this paper. When it comes to this big question (which is morally close to the question "how much we have proven that a consistent theory of quantum gravity has to be string/M-theory"), the paper by Aalsma et al. – albeit a very interesting paper – may be considered a rationalization of one possible answer ("Yes, stringiness is demonstrably essential for QG to work"), not really an impartial proof that this answer is better than the other answer.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-5584821198353530342019-05-17T08:15:00.001+02:002019-05-17T08:27:09.928+02:00Heckman, Vafa: QG bounds the number of hierarchy-like problemsEvery competent physicist knows that fine-tuning is a kind of a problem for a theory claimed to be a sufficiently fundamental description of Nature.<br /><br />Fundamental physicists have wrestled with the cosmological constant problem, the Higgs hierarchy problem,... and perhaps other problems of this kind. Fine-tuning is a problem because assuming that the fundamental "theory of everything" works like a quantum field theory and produces the couplings of the low-energy effective field theories via renormalization group flows, the observed hierarchies between the scales etc. seem extremely unlikely to emerge.<br /><br />In principle, there could be arbitrarily many couplings and even fine-tuned couplings which could cause an infinite headache to every theorist. In a new paper, Cumrun Vafa – the Father of F-theory and the Swampland Program (where this paper belongs) – and Jonathan Heckman, a top young research on both topics, present the optimistic evidence that in string/M-theory and/or quantum gravity, the infinite fine-tuning worries are probably unjustified:<br /><blockquote><a href="https://arxiv.org/abs/1905.06342">Fine Tuning, Sequestering, and the Swampland</a> (just 7 pages, try to read all)<br /></blockquote>What's going on? Effective field theories outside quantum gravity may be built by "engineers". You may apparently always add new fields, new sectors, and they allow you to tune or fine-tune many new couplings. There doesn't seem to be a limit.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />String/M-theory is more predictive and chances are that even if there were another consistent theory of quantum gravity, it would be more predictive, too. In particular, as they say, the number of couplings that can be independently fine-tuned to unnatural values is finite. <br /><br />I have a feeling that they count the moduli among the couplings that can be "fine-tuned", even if they correspond to physical fields. But that doesn't invalidate their statement because they say that the number of moduli is bounded, too.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Moreover, the bound is a fixed finite number for every choice of the number of large dimensions and the number of supercharges. Fine, what's the evidence?<br /><br />First, the number of the Minkowski, flat spacetime solutions in string/M-theory seems to be finite. Also, the number of Calabi-Yau topologies seems to be finite. The latter statement hasn't been quite proven but propositions that are very close have been proven. For example, if you restrict the manifolds to be elliptically fibered and the base to be a toric geometry, it's been proven that Calabi-Yau three-fold topologies form a finite set. It seems very likely that the manifolds that cannot be represented like that are a "minority", so even the number of all Calabi-Yau topologies should be finite.<br /><br />Their first full-blown discussion is in 6D field theories. Conformal field theories have either \((1,0)\) or \((2,0)\) supersymmetry; \((1,1)\) cannot be conformal. Infinitely many classes of such theories with lots of deformations exist as CFTs. But if you want to couple them to gravity, you see restrictions. The cancellation of anomalies requires the total number of tensor multiplets to be 21 which is a particular finite number. In fact, all stringy 6D CFTs only allow deformations that result from operators that exist in the theory. In this 6D case, their new principle largely reduces to the anomaly cancellation.<br /><br />In another related example, the total rank of some gauge group is 22. Perturbative string theory obviously restricts these ranks by the central charge – the rank cannot be too high for the same reason why the spacetime dimension cannot be arbitrarily high. Well, the central charge is also a gravitational anomaly – on the world sheet.<br /><br />They discuss a few more rather specific examples – so their paper has many more equations and inequalities than what is actually needed for their main claims. But the overall new swampland principle has ramifications. In particular, if you imagine many sequestered or hidden sectors in artificially engineered apartheid-style models of particle physics, all their couplings seem to be independent, and could therefore admit independent fine-tuning.<br /><br />According to Heckman and Vafa, if the number of such sectors is too high, quantum gravity actually implies some correlation between the fine-tunings. At the level of effective field theory without gravity, many parameters \(g_i\) could be independently adjusted and very small. But if you require that the theory may be coupled to quantum gravity, it already follows that there are equations that correlate almost all these constants \(g_i\), up to a finite (pre-determined) number of exceptions.<br /><br />Sometimes people express their doubts about the reasoning involving naturalness and the disfavoring of fine-tuned theories. Indeed, the thinking based on quantum field theories is ultimately imprecise and incomplete and has to be adjusted. But "just ignore all the fine-tuning problems" isn't a scientifically valid adjustment to the problem. The problems cannot be completely ignored because they're implied to be problems by a rather specific, successful framework of physics that we use all the time – quantum field theory – combined with the probability calculus. To ignore the problem would mean to cherry-pick what we like about the framework – quantum field theory – and what we don't.<br /><br />Instead, the adjustment to the fine-tuning rules must have the form of "quantum field theory isn't an exact description of Nature and the correct framework differs in respects A,B,C, and these differences also imply different predictions concerning the fine-tuning". This new Heckman-Vafa swampland may be counted as an actual <em>scientific</em> way to go beyond the existing rules about the naturalness and fine-tuning in effective field theories. The paper tells us how string/M-theory <em>actually</em> modifies the semi-rigorously proven intuition or lore about the fine-tuning in our effective field theories. <br /><br />The modification primarily says that the couplings are automatically more constrained than naively indicated by the low-energy effective field theory analysis. In other words, string/M-theory is – in a new specific sense – more predictive than quantum field theory. It shouldn't be surprising because quantum gravity needs to reconcile the low-energy behavior with the high-energy behavior – where the particle spectrum must gradually merge with the black hole microstates whose entropy is again dictated by a low-energy effective field theory (including Einstein's gravity). When you're playing with the low-energy couplings, quantum gravity actually tells you that you have to aim at and hit several targets for the trans-Planckian behavior of the theory to remain consistent (with gravity).Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-3291177966943201782019-05-14T07:22:00.002+02:002019-05-15T10:59:02.128+02:00EVs vs ICEs, NOx, critics of science as thought police, Ponzi scheme, SophThere are too many terrible events happening in the world right now – every day, both famous and unknown people are getting fired and hunted for saying the truth or for not being far left extremists; scientifically illiterate snake oil salesmen are receiving the Hawking Prizes; media are bombarding us with lies against science and the Western civilization.<br /><br /><a href="https://www.volkskrant.nl/wetenschap/parallelle-universums-tijdmachines-zijn-theoretisch-fysici-de-weg-kwijt~b18fa264/" rel="nofollow">A major Dutch publication</a> has written a text on the topic "is physics a Ponzi scheme?". My once co-author Robbert Dijkgraaf and Juan Maldacena are the only voices that actually and calmly explain the state of theoretical physics now. They're overwhelmed by critics who don't understand the field at the technical level at all and who are being presented as if they were equal – Maldacena is the top theoretical physicist of his generation and Dijkgraaf is, among other things, the director of IAS Princeton where Einstein used to work.<br /><br />Those special attributes don't seem to matter to the journalists anymore. Random angry activists and hecklers who are allies of the journalists are often made more visible.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />The critics say it's very important that they're receiving supportive e-mail from other scientifically illiterate laymen and the journalist implicitly agrees with that. Meanwhile, Robbert is correctly pointing out that research works when it's not constrained by a thought police. These witch hunts against physics are obviously just another part of the thought police that is gaining strength in our society – and theoretical physics is naturally another expected target of the far left movement, as something evil because it has been overwhelmingly built by the white males. People who don't have the ability to do meaningful science are being happily hired by the fake news media as the inquisitors who are presented as equal to the top physicists.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />This anti-meritocratic distortion of the life, Universe, and everything in the media affects all fields and all age groups. A hysterical (adjective chosen by Czech president Zeman), inarticulate, brainwashed, psychologically troubled 16-year-old Swedish girl who believes that the Earth is burning – probably much like an <a href="https://youtu.be/sUFugN6wo7Q?t=41">impolite Bill Nye with a flamethrower</a> – is presented as a celebrity. (Sorry, the IQ of the people who are affected by these things by Bill Nye has to be so low that I refuse to count them as full-blown members of the homo sapiens species.) Readers are supposed to be interested in her book deal – she can obviously write just a worthless incoherent rant because she is not an intelligent girl, and this rant will be written by some older but almost equally unremarkable environmentalist activists, anyway.<br /><br /><b>Meanwhile, the contemporary teenagers are way more conservative and sensible than the millennial generation. Everyone who cares about the future of mankind must make sure that this generation will grow into a pro-Western, sane, mostly right-wing bunch. And it's possible. We must only start to care about the education!</b><br /><br />OK, there's a wonderful comparison of Greta Thunberg with someone on the other side. If you don't know her, look at the videos by <a href="https://www.youtube.com/channel/UCT7BLBDnD-wEXeqZSg24aJw/videos" rel="nofollow">Soph</a>. Soph is a 14-year-old (*9/23/2004 as Sophia Totterman) girl – two years younger than Greta Thunberg – whose YouTube videos (don't be afraid and try the latest <a href="https://www.youtube.com/watch?v=OdaUDeAGIck" rel="nofollow">Be Not Afraid</a>) get three hundred thousand views per video in average. (Update: hours after this blog post was posted, this particular latest excellent video by Soph was removed by some nasty YouTube aßholes as "hate speech". It was far from the only one. Here you have a <a href="https://www.bitchute.com/video/OdaUDeAGIck/" rel="nofollow">backup</a>.) And she is discussing rather adult topics, indeed (starting with the co-existence of cultures and high school students' life). By the counting of the viewers, this girl is a self-made millionaire (OK, I still believe that there are some adults helping her with her videos – she says the older brother is a key but they say she's more radical than he is – but the result looks both more true, more impressive, more entertaining, and more authentic than Thunberg's). Do the media celebrate an actually brilliant girl who has achieved something by herself, without the media machinery? <br /><br />Not at all. In fact, the answer "not at all" is far too optimistic. Yesterday, Joseph Bernstein wrote a disgusting hit piece against the 14-year-old girl at <a href="https://www.buzzfeednews.com/article/josephbernstein/youtubes-newest-far-right-foul-mouthed-red-pilling-star-is">BuzzFeed News</a>. Using a giant media machinery to attack teenage girls is how your far left movement defines a Gentleman today, isn't it? <br /><br />Mr Bernstein, it hurts when someone is 14-year-old and more sophisticated and smarter than you and all your far left comrades combined, doesn't it? She makes you realize where (in the political sense) are the people who have some talent – and which remainder of the mankind is just a field of weeds that fail to achieve anything remarkable despite their usage of all immoral and illegitimate tools and weapons we may think of. And you dislike the truth, don't you? Soph's sentence that follows your "or how about, simply" is spot on.<br /><br />In two or three decades, if the likes of Soph happen to be outnumbered by the brainwashed sheep of her generation, Soph et al. will have the duty to fully appreciate that she's equivalent to 100 or so sheep, and adjust the rules of democracy accordingly. It will be your world, Soph, and you can't allow sheep to overtake it.<hr><br />But I want to talk about a relatively lighter topic, the electric vehicles (EVs). OK, so we have exchanged some e-mails with Gene about the advantages and disadvantages of EVs and cars with internal combustion engines (ICEs). I won't cite the precise sentences but I needed to mention the e-mail conversation for you to understand why I was surprised by Gene's comments posted a few hours ago that indicated that I should celebrate Brussels for encouraging Audi to produce EVs.<br /><br />What? Surely you have understood that I am absolutely against this push to spread EVs by now, Gene. And indeed, this push is largely empowered by the European Union. It's another example of the criminal behavior of that international organization, a reason why most of the powers that this organization has acquired must be reversed, another reason to disband the EU in its current form.<br /><br />Just days ago, I translated <a href="https://motls.blogspot.com/2019/05/neff-when-reason-is-pushed.html?m=1">Ondřej Neff's essay</a> which clearly stated that the statements by the Volkswagen Group that they only want to produce EVs in 2030 or something like that are terrifying, sick, ideologically driven, and directly threatening at least a quarter of the Czech economy. You won't get any support of mine for the EVs from Audi. They may produce some, the products may have some good characteristics, they will probably lose money on them, but the idea that this should be supported – and maybe even by the likes of me – is absolutely insane.<br /><br />Gene pretends to be more open-minded and less ideological than the rest of Northern California and maybe he is. But I still find his PC virtue signaling unbearable way too often. He must have understood that I am generally against the expansion of the EVs at the moment because the disadvantages clearly trump the advantages. Have I been unclear about this elementary point? I don't believe it's possible. So why would Gene assume that I am going to praise the EU for Audi's EVs? Let me tell you why.<br /><br />He doesn't really believe it but he's one of the promoters of this ideology – and a part of the strategy of such people is to create the atmosphere in which it is "believed" that all the people, perhaps including your humble correspondent, support the transition to EVs. He likes to strengthen the perception that the preference for ICEs is an unthinkable heresy, a thought crime – and he personally helps to nurture this atmosphere of non-freedom. I don't support the transition to EVs. Do you need this simple sentence to be translated to many languages? Sensible people who have thought about the issue know that the ICEs are superior at this moment and the EVs are inferior and if someone is telling you something else, he is not saying the truth.<br /><br />The price that the actual buyer pays for an EV – when the vehicle is bought in the first place – is about twice as high than for an otherwise comparable ICE right now. This is the primary difference which is enough to conclude that the EVs are simply not competitive with the ICEs now. But even if the progress were much faster in EVs than ICEs – there's no reason to believe so – and EVs became as cheap as comparable ICEs, ICEs would still have other, secondary but very important, advantages.<br /><br />These advantages of the ICEs, if I include the lower price, are e.g.:<br /><ol><li>lower price of the vehicle in the first place</li><li>much shorter refuelling times of the ICEs than charging times of EVs</li><li>existing network of gas stations, minimum of superchargers</li><li>environmental disadvantages of EVs: toxic elements</li><li>safety involving some special processes, e.g. self-ignition of EVs</li><li>a centennial experience with the ICEs showing that there's no time bomb waiting for us</li></ol>This list is far from complete but it's quite a list. The price of the car is clearly a primary variable and the ICEs win 2-to-1 over EVs. The charging times are incomparable. You spend a few minutes by refuelling petrol or diesel but you need 20-40 minutes to recharge 50-80 percent of a Tesla battery. This difference is huge, I will discuss it later.<br /><br />Now, you only recharge an EV if you're lucky and there's a nearby supercharger. Are these networks comparable? Czechia gives us a shocking example. We have over 7,000 gas stations and <a href="https://www.tesla.com/en_GB/findus/list/superchargers/Czech%20Republic?redirect=no">3 Tesla superchargers</a> – in Prague, Humpolec, and Olomouc. That's where you recharge the car as "quickly" as in 30 minutes. Outside these places, you find at least overnight chargers where you need to be connected... you know, overnight.<br /><br />Now, will the network of superchargers grow? It will. Will it be fast? Are there good reasons for the growth? There aren't because the number of EVs is small. So it's clearly too bad an investment to build too many chargers for too few EVs. This is a vicious circle. A century ago, a similar "vicious circle" arguably slowed down the growth of the normal gas stations. But there was a difference. A century ago, ICEs were competing against <em>horses</em>, and cars are more convenient than horses even <em>despite</em> the rare network of gas stations.<br /><br />Now, the EVs are competing against the ICEs which are really comparable – it's not a difference similar to the difference between a horse and a car. So the construction of a dense network of superchargers is clearly an investment that will create a financial loss for quite some time. The belief that it's worth to do it is just a belief. And it is clearly a belief that is driven by an ideology right now.<br /><br />I mentioned that there are 7,000+ gas stations and 3 Tesla superchargers in my country. The ratio looks huge. But what about the ratio of the cars? In 2018, Czechs bought some 250,000+ new cars, about 30% of them were diesel, a drop from 37% in the previous year. Aside from petrol and diesel, all the other cars are <a href="http://www.hybrid.cz/rok-2018-v-cesku-diesel-se-propada-rekordni-prodeje-elektromobilu-skvele-si-vedou-i-hybridy" rel="nofollow">negligible</a>: 5,000 hybrids, 2,000 CNGs, 1,000 LNGs, and 1,000 purely electric vehicles, including 85 Teslas. In 2018, 0.03% of the cars sold in Czechia were Teslas. 3 superchargers are 0.05% of the 7,000 gas stations – so within a factor of two, it's fair.<br /><br />There is absolutely no reason to think that the EVs will naturally beat the ICEs anytime soon. In particular, the market obviously wants to keep the petrol/diesel gas stations up to 2030 because in 2030, there will still be lots of cars purchased recently because it's normal for many people to keep the same car for a decade.<br /><br />Now, the environmental advantages of ICEs. They produce just H2O (water vapor) and CO2, harmless and beneficial gases. There's some NOx, nitrogen's oxides, in the diesel case. This must be compared to the noxious elements that are used in the production of the batteries for EVs, that occasionally burn when a car self-ignites (Hong Kong saw another self-igniting Tesla yesterday) or when a whole EV factory burns (which seems to be a frequent event, too). People don't really know whether it's possible to safely deal with the worn old lithium batteries.<br /><br />Gene admits that the real pollution from ICEs is much smaller than it used to be – a drop by 97%, using his numbers. But even the world with the high pollution was OK enough. When it drops to 3% to what it used to be, should we still consider the situation unacceptable? I don't think so. This opinion is nothing else than an extremist ideology. Look at the death rates.<br /><br />Every year, some 1.3 million people die in the world as a result of a car accident – some mechanical damage to the body. It's estimated that the NOx emissions may be blamed for 10,000 deaths in the EU per year. The total for the world is probably below 100,000. Now, is it too high? It's clearly not too high. The deaths blamed on the <em>fuel</em> are less than 10%, and maybe around 5%, of the deaths caused by the vehicles in total. In what sense could we claim that it's too much?<br /><br />Every year, some 55 million people die globally. Those 50,000-100,000 from NOx are between 0.1% and 0.2% of the deaths. If you eliminated petrol and especially diesel cars, you would reduce the deaths by 0.1%-0.2% or so. Great. Temporarily, of course. After some time, the population would be upgraded to a higher life expectancy and the same number of people would be dying at a higher age as without the reduction of NOx.<br /><br />But imagine that the ratio of the deaths is comparable to the increase of the life expectancy – it's not quite so but it's a good order-of-magnitude estimate. So the NOx emissions from cars may be reducing the lives of the people by 0.1% or 0.2%. Great. What about the waiting times in front of the superchargers? If you recharge every other day, you waste 30 minutes per 2 days (48 hours) in front of the supercharger. That's about 1% of your time! To a large extent, this has shortened your useful life. And 1% is 5-10 times larger than 0.1% or 0.2%. <br /><br />The result is that the superchargers are robbing you of a greater portion of your life than the NOx car pollution in average!<br /><br />Even if CO2 emissions were a problem, and they're not, one may show that in the present real-world conditions, the total CO2 emissions connected with the production and usage of an EV actually trump those of a diesel car.<br /><br />It's similar with all such comparisons. If you actually compare the variables on both sides fairly, you may see that the ICEs are superior than the EVs. It may change in some time – as the technologies evolve – but the difference is so significant that it's unlikely to change for many years. But this discussion has been largely hijacked by dishonest ideologues who are close to the environmentalist movement and the deceptive "mainstream" media of the present. Because they have decided to stick this particular EV agenda mindlessly, they only push memes about advantages of EVs and disadvantages of ICEs down into their viewers' and readers' throats. Virtually all of this is garbage. People intuitively know it – they subconsciously perform many of these calculations which make them keep their ICEs and avoid EVs. But the massage by the media and their allied ideologues is unbelievable. The percentage of the EVs in a given country or state may be considered a very good measure of "how much the population of that territory likes to be brainwashed".<br /><br /><b>Now, advocates of EVs also say that the EVs are simpler, and therefore less likely to break.</b><br /><br />This is another totally demagogical sleight-of-hand. EVs have fewer mechanically moving parts but they have a greater number of "transistors" and other electronic parts. Can they break? You bet. The electric cars depend on lots of software and it can break – and cripple your car – too. It's happening. Functionalities of cars are often broken after a software update. It's completely analogous to the mechanical breaking of an ICE. More importantly, the probability that an engine breaks isn't a simple increasing function of the "number of parts". It depends which parts, how well they're made, how robust the material is, and other things.<br /><br />In practice, the breaking of the ICEs is not such a problem. Many problems may be fixed. It's been business-as-usual for a century. And we don't really want to assume that the cars serve for more than 20 years or something like that. Cars that are this old look obsolete. They have other disadvantages. People usually prefer to buy a new car after a shorter time – perhaps 5 years in such cases – and carmakers obviously want this "refreshment" to take place sufficiently often, too. So the "simplicity advantage" of the EVs only exists under assumptions that are utterly unrealistic.<br /><br />Even more conceptually, simplicity is heavily overrated. I have also often said that I preferred things to be simple. But I saw others saying similar things – and saw that their reasons for saying such things are totally bad. In most cases, people say "they prefer simple things" because they're lazy or intellectual limited. They want "things" to be simpler because harder things mean extra work for them and they don't like it! It's that simple. My explanation is actually <em>simple</em> which is why you should appreciate it! It's also true. That's why schoolkids prefer a simple homework, for example. There may exist legitimate justifications of "simplicity" but they're rare.<br /><br />But does it mean that "simple" is "superior" in general? Not at all. The schoolkids and their adult counterparts are doing some work. And if the work were "simple", it probably means that they didn't do too much work, and that's "bad" for the client or buyer. The buyer has a completely different perspective than the producer. If something is simple, it should often be expected to be cheap and unremarkable because not much work has been done! There is almost nothing inside the Tesla Model 3's interior which is why it should be an extremely cheap car. An extensive essay should be written about the simplicity in fundamental physics – which is a sufficiently different topic than simplicity in engineering. We prefer as simple things as possible, but not more so, as Einstein wisely said. Again, the laymen usually want things to be simpler than possible and that's too bad.<br /><br />This "simplicity" has been added to the preferred buzzwords of the Luddite movement, too. "Simple" things are supposed to be preferred. That may include organic food. But much of this "simple" stuff is the same as the "cheap stuff before the technological advances reshaped the industry". So the "simplicity" often directly contradicts "technological progress"! It's not a shame for an engineer to design complex engines. If someone denies that this is really the bulk of the work of every engineer, then this someone is a Luddite who fights against the technological progress in general. And even complex engines may be made more reliable, more resilient, and more lasting. "Complexity of an engine" isn't any insurmountable lethal flaw.<br /><br />An ICE has a lot of parts, especially if it has various gadgets to reduce emissions of various compounds or particles. But that doesn't mean that it's bad. Complex engines are the standard product of engineering. Engineering also wants to keep things simple <em>if all other things are equal</em>. But the "if" condition isn't obeyed here – it is almost never obeyed. Things aren't equal. You can't compare things that aren't commensurable. And the "number of parts in an EV or an ICE" is not commensurable. To achieve certain things, a certain degree of complexity is often needed – EVs and ICEs mainly have a different <em>kind</em> of complexity, not a different amount. So we just don't want things to be too simple. At the end, a car or a phone should have "many functionalities" and some complexity is necessary for that. In the 1980s, I was surely happy that my watch received from my Australian uncle had a calculator, stopwatch, and many other functions. Whoever thinks that a small number of functions is a universal advantage is simply a Luddite.<br /><br />Now, Gene and others say that "the market will decide". But sadly, that's not what is happening today. Liars and charlatans in the media and unelected EU officials who are actually controlled by brain-dead members of various NGOs and other pig farms owned by the likes of George Soros are determining whether companies – perhaps, by 2030, including Škoda Auto – will be allowed to produce proper cars that the consumers actually want at all, and whether the buyers will be "allowed" to buy the cars of the kind they prefer. It's too bad.<br /><br />In 2019, EVs are a niche market and every argument building on the assumption that the EVs are as important as or more important than the ICEs is just self-evidently fraudulent. If it is allowed to speak, the market will speak but to some extent, it has already spoken, too. Both EVs and ICEs have been around for more than a century but ICEs became and remained dominant. Given the political atmosphere and the amount of lies and illegitimate pressures that we see everywhere around, it seems very likely that a hypothetical suppression of ICEs and proliferation of EVs may be explained by the emerging totalitarianism, not by the natural and legitimate market forces.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-28035283474167660712019-05-10T11:48:00.000+02:002019-05-10T11:56:58.286+02:00Pheno papers on \(96\GeV\) Higgs, trilepton excess, and \(60\GeV\) dark matterI want to mention two new hep-ph papers about supersymmetry-like anomalies seen by the accelerators. In the paper<br /><blockquote><a href="https://arxiv.org/abs/1905.03280">An N2HDM Solution for the possible \(96\GeV\) Excess</a>,<br /></blockquote>B+C+Heinemeyer discuss some detailed models for the apparent weak signals indicating a <a href="https://motls.blogspot.com/2017/09/cms-locally-28-sigma-diphoton-excess-at.html?m=1">new Higgs boson of mass around \(96\GeV\)</a>. Recall that the only well-established Higgs boson has the mass of \(125\GeV\).<br /><br />Concerning the \(96\GeV\) little brother, the CMS has seen an excess in the diphoton channel; and decades ago, LEP has seen an excess in the bottom quark pair channel. Heinemeyer and friends say that these excesses may be explained by a two-Higgs model with an extra Higgs singlet. Is that surprising at all? There seems to be a lot of freedom to accommodate two independent excesses, right?<br /><br />At any rate, concerning supersymmetric models, the NMSSM – next-to-minimal supersymmetric standard model – and its extension, µνSSM seem like aesthetically pleasing completions of the two-Higgs-plus-a-singlet models. In the model with the two Greek letters, the singlet is interpreted as a right-handed neutrino superfield and the seesaw mechanism is incorporated. These models look OK for the excesses – there are other reasons to prefer NMSSM over MSSM. But they're also less constrained and predictive than the MSSM, so I think the good news isn't remarkably victorious.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Another paper on the excesses is<br /><blockquote><a href="https://arxiv.org/abs/1905.03768">The Return of the WIMP: Missing Energy Signals and the Galactic Center Excess</a><br /></blockquote>by Carena+Osborne+Shah+Wagner. They promote a model with the dark matter of mass \(m_\chi = 60\GeV\) and its justification by anomalies that exist out there.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />The dark matter of that mass would be the lightest neutralino. It could naturally agree with the 3-sigma <a href="https://arxiv.org/abs/1806.02293">trilepton ATLAS excess</a> (and a confirmation by GAMBIT), the gamma <a href="https://motls.blogspot.com/2013/03/bubbles-support-10-gev-or-50-gev-dark.html?m=1">ray excess at the center of our galaxy</a> seen by Fermi-LAT, as well as the <a href="https://motls.blogspot.com/2016/12/sam-ting-claims-that-1-tev-wimp-is-only.html?m=1">antiproton excess observed by AMS-02</a>.<br /><br />In their model, the LSP is a bino-like neutralino and another, wino-like neutralino should exist with the mass of \(160\GeV\). \(\tan\beta\) should be greater than ten. This paper may be viewed as a counter-argument against the recent efforts to claim that the central galactic gamma-ray excess was "due to some boring pulsars" only.<br /><br />At any rate, dark matter of mass \(60\GeV\) within supersymmetry is still plausible and somewhat recommended by some observations, much like the NMSSM-like new Higgs of mass \(96\GeV\). I can't tell you the probability that these particles exist – it depends on lots of priors and methodology – but I am sure that it is just wrong and prejudiced to behave as if these probabilities were zero.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-26722179952270949442019-05-07T06:52:00.001+02:002019-05-07T08:19:13.542+02:00Carroll's interview with SusskindOn his Mindscape Podcast (<a href="http://seancarroll.libsyn.com/rss" rel="nofollow">RSS subscribe URL</a>), Sean Carroll published an unusually good 74-minute-long interview with Leonard Susskind:<br /><blockquote><a href="https://www.preposterousuniverse.com/podcast/2019/05/06/episode-45-leonard-susskind-on-quantum-information-quantum-gravity-and-holography/">Episode 45: Leonard Susskind on Quantum Information, Quantum Gravity, and Holography</a> (audio)<br /><br /><audio class="wp-audio-shortcode" id="audio-2327-1" preload="none" style="width: 100%;" controls="controls"><source type="audio/mpeg" src="https://chtbl.com/track/15E2/traffic.libsyn.com/seancarroll/leonard-susskind2.mp3?_=1" /><a href="https://chtbl.com/track/15E2/traffic.libsyn.com/seancarroll/leonard-susskind2.mp3">https://chtbl.com/track/15E2/traffic.libsyn.com/seancarroll/leonard-susskind2.mp3</a></audio><br /><br /></blockquote>Both men are very good speakers and in this case, especially because he has avoided words like "many worlds" (he preferred "agnostic"), "Donald", and others, I could have subscribed to nearly 100% of Susskind's statements. <br /><br /><img src="https://upload.wikimedia.org/wikipedia/commons/e/e0/Leonard_Susskind_at_Stanford.jpg" width=407><br /><br />Susskind was introduced as a visionary, storyteller, mentor, a co-father of string theory who has done a lot in QFT, a popularizer etc. He prefers to call himself "a theoretical physicist" rather than a "string theorist" because it gives him more freedom to jump around, to be researching anything he wants, and to be bullšiting about anything he wants (the B-verb actually <em>is</em> Susskind's favorite word, but you can't know it if you don't know him in person and if you're not a TRF reader).<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Concerning the value of string theory, Susskind primarily said that it has given us extremely accurate models which contain quantum mechanics, gravity, electromagnetism, particles, bosons, fermions etc. – so we know for sure that these properties of the Universe are compatible with each other, which hadn't been clear at the beginning, and it's a big deal even if we're not sure it's the theory of the real Universe around us.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Susskind is also asked to sketch the information loss paradox. The information is preserved, quantum mechanics won. Carroll asked Susskind about his love for an alternative picture – the time becomes a rope that chokes itself inside the black hole, which causes an abortion and the aborted baby universe makes everything fine or something like that – and Susskind said No. But this is a great alternative theory by philosopher Tim Maudlin, don't you know this genius? Good for Lenny, he doesn't know Maudlin. You would know dozens of such wannabe physics revolutionaries if you spent more time with the Internet, Lenny! <br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=0465093345&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>The black hole evaporates at the end so every "natural" time slicing "after" the evaporation agrees that nothing is left from the black hole whatsoever, except for ordinary particles from the Hawking radiation. The baby time inside the black hole... it's just some random talk that could have been widespread in the 1970s but there is absolutely no mathematical backing for these philosophical words. Science went elsewhere, Carroll's apparent defense of Maudlin's nonsensical story notwithstanding.<br /><br />Susskind discussed the no-cloning theorem in quantum mechanics: quantum information cannot be duplicated. He had thought he discovered the no-xerox theorem but it turned out that he only discovered the new corporate branding term for the previously known no-cloning theorem. The duplication is a problem, conflicts with linearity of QM (duplication is a quadratic map, I add), and there was a discussion whether the duplication "as such" has to be banned or whether any <em>detection of duplication</em> has to be banned.<br /><br />In this discussion, like in most others, Susskind was the wiser one and pointed out that it's the latter. A potential paradox may make you nervous but it only becomes a real paradox if it can actually be measured. Needless to say, Carroll – the "realist" who still thinks that classical physics is right (not that Susskind may always be said to avoid this basic mistake, but he does avoid the anti-quantum zeal in his positive stories here) – disliked all these comments. Carroll also made some totally wrong statements about Heisenberg's uncertainty principle such as "neither the position nor the momentum of a particle exist, only the wave function does". No, it's the other way around. Physically, only observables – such as the position and momentum – really exist because they're "observable", that's why they are called in this way, while the wave function is <em>not</em> an observable, and it is not observable without "an", either.<br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=0465062903&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>OK, Lenny's careful formulation is that any attempt to observe both \(x,p\) – and similarly any attempt to observe the duplication – will always get frustrated. Exactly. If you can measure what's inside, you can't measure what's outside, and vice versa. Well, it's not just analogous to the uncertainty principle for \(x,p\), it's really a special case. The relevant operators inside and outside refuse to exactly commute, as locality would predict.<br /><br />For example, if you collect enough information from the Hawking radiation, and you want to fall into the black hole and see the same information inside once again, you will fail because the "collection" requires a certain time and a hard calculation shows that that somewhat surprisingly, after that time, the original matter is already destroyed at the singularity. So the physical dynamics doesn't necessarily avoid the paradox immediately, by some urgent immediate huge prevention policies, but the physical dynamics always prevents the paradox, sometimes "barely" or "at the last moment". This is enough and quantum gravity or string theory <em>love</em> to save the consistency "at the last moment".<br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=0465075681&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>This time, thankfully, Susskind calls himself an agnostic on interpretations of quantum mechanics – "uncertain whether there is a problem", a phrase he copied from his friend Feynman. QM will always work. But he can't get rid of some confusion about the relationships of QM and reality. Quantum gravity/cosmology will probably affect the foundations, he thinks. Possible, indeed. It won't happen in Susskind's lifetime, he thinks. Carroll promoted some "work" of his on the anti-quantum zeal, Susskind politely avoided commenting on that even though some of Susskind's papers could be claimed to be in nearly the same category.<br /><br />Why would someone think something as crazy as the holographic principle (independently found by Susskind and 't Hooft), Susskind is asked? There are entropy bounds. Volume and information are proportional for a while but if you put too many memory chips in a volume, they collapse in a black hole that is larger than the originally reserved volume. Some insights from the 1970s are recalled. Another level above the entropy bounds is a hypothetical theory that lives on the boundary. 't Hooft's paper looked worth ignoring to most physicists because he had used the term "dimensional reduction" incorrectly, Susskind recalls. Susskind chose a better word in the title, "hologram", and physicists started to understand stuff. Witten liked the principle but Juan Maldacena finally turned holography into an almost clearcut rigorous construction and a tool. Susskind claims that Maldacena had not known Susskind's and 't Hooft's papers on holography. Note that for Maldacena, AdS/CFT was a ramification of his work on the Strominger-Vafa-like black hole entropy in string theory. The acronym AdS/CFT is expanded with some history about de Sitter, that Susskind clearly doesn't know too well, and neither do I. AdS has negative energy density. Witten, familiar with Susskind's and Maldacena's papers, introduced the term "holography" to AdS/CFT (along with a whole machinery to compute the correlation functions but Carroll and Susskind skip such details LOL).<br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=0316016411&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>Susskind admitted we still don't have an idea how to build a holographic theory for a generic "finite region". I find it plausible that no such nice theory exists. In particular, I think one can almost prove that such a theory on a generic finite surface couldn't be local. In AdS/CFT, the boundary CFTs are local because of the infinite warp factor – it seems like a necessary condition for the locality.<br /><br />"What do we learn from the weird construction?" Carroll asks. He may play a Devil's advocate but it looks he is serious. "What do we ever learn?" Susskind replies. Susskind then clarifies that theories aren't always obtained by quantizing a classical starting point, and this "quantization of classical" is dysfunctional for gravity. Maybe the difficulty is because gravity and QM are worlds apart. Susskind thinks that the resolution is the opposite one: gravity and QM are too close and the problems in "quantizing GR" come from the efforts to <em>separate</em> these almost identical things. Susskind described a nice experiment showing the inseparability of gravity – it could be done as a quantum computer simulation. He talked about general simulations of superconductors at quantum computers and other things. And about quantum error correction, something that wasn't needed in classical computers due to the resiliency of classical bits. Cutely, black hole research has led to advances in the real practical error correction industry. His only example is ER-EPR.<br /><br />Now, Carroll repeated some weird doubts about holography. How much is holography relevant for the tables around just "crossing our fingers"? I think it's hard to answer such vague questions whose only comprehensible content is hostility. Susskind didn't lose his nerves, as I could have ;-), and repeated the basic point. We have found a theory that has QM, GR, particles, all the basic qualitative things, and within its AdS spacetimes, the AdS/CFT is true. Does it prove that holography is always true, especially in the real world? Strictly speaking no. But it excludes the assumption that one could have – and Carroll probably has it – that holography is ludicrous or impossible. There's no question that holography may happen now, especially in AdS spaces. In dS spaces, we're less confident.<br /><br />The interview was recorded in the Google X buildings because they have been consultants. Susskind discusses how he learned some complexity theory in the computer science sense – the absolute possible minimum number of steps from A to B. Susskind celebrates the genuine collaboration between computation guys and theoretical physicists. Good ideas often penetrate to many directions and that's how you know that there's something strong about them. Examples involving condensed matter physics, fluids, and black holes follow. The SYK model was invented by Sachdev, a Harvard CM physicist. Great but Subir is also a de facto string theorist now so this example of multiculturalism isn't "too" multicultural. OK, at any rate, SYK stands for a condensed matter physicist, an information physicist... and it's used in the black hole research.<br /><br /><a href="https://lh5.ggpht.com/lubos.motl/SLzWAIwIlpI/AAAAAAAAA5I/l6c7FCXx4Jk/dienes-lennek-9-landscapes.jpg?imgmax=1600" rel="nofollow"><img src="https://lh5.ggpht.com/lubos.motl/SLzWAIwIlpI/AAAAAAAAA5I/l6c7FCXx4Jk/dienes-lennek-9-landscapes.jpg?imgmax=400"></a><br /><br />Ten minutes before the end, Susskind says that the multiverse (a package of many patches, like jungle, savana etc.) is still the best picture for the biggest questions and for fine-tuning in cosmology. He always asks for better things and the answers come out empty. It may turn out to be wrong but Susskind doesn't see how. Also, we know that the Universe is bigger than the visible portion – just like we know it for the Earth. Both are very flat. CNN may write about the Stanford professor who believes in a very "Flat Earth". ;-)<br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=B000SEOB2Q&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>Susskind doesn't want to predict the next revolution in physics but thinks that strings, qubits etc. will have to address the cosmological questions. The proper relationship is unknown.<br /><br />Carroll asks why Susskind did the popularization, like the popular books. It was done for Susskind's father who was a plumber with a simple education – but with other plumbers in Bronx, these rough men were intellectuals. They talked about everything, history, science – a nice mixture of intellectualism and crackpotism. And Susskind obviously believes that the crackpotism was due to no access to science literature. Susskind believes that he has taught some science to his father. Well, I don't believe these things much. People's crackpotism is <em>not primarily</em> due to the bad access to scientific research. OK, some people in Palo Alto were already annoyed by Susskind's SciAm-level talk, and wanted real physics with equations, so he did some. That's where the Theoretical Minimum came from.<br /><br />Right, it's important to explain science at a decent level. But I think that there's something more fundamental that decides about people's scientific approach than some detailed equations. It's some understanding why and when the equations should be taken seriously at all. I think that most people who are exposed to equations don't connect them with the reality because they misunderstanding something more conceptual about how science works – so they end up lost in mathematics. Some hardwired irrational disbelief that "equations may not or should not really be decisive" is the main stumbling block that keeps otherwise capable people's thinking about the physical world unscientific.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-41124065833615378482019-05-06T17:56:00.001+02:002019-05-06T18:25:55.320+02:00Axion weak gravity conjecture passes an extreme Calabi-Yau testThe first hep-th paper today was posted 1 second after the new business day at arXiv.org started, indicating that Grimm and van de Heisteeg (Utrecht) really think that people should read their paper:<br /><blockquote><a href="https://arxiv.org/abs/1905.00901">Infinite Distances and the Axion Weak Gravity Conjecture</a><br /></blockquote>The first thing I needed to clarify was "what is the exact form of the 'axion weak gravity conjecture'" that they are using. There must surely be a standalone paper that formulates this variation of our conjecture. And oops, the relevant paper was <a href="https://arxiv.org/abs/hep-th/0601001">[4] AMNV</a>. I have already heard the M-name somewhere.<br /><br /><iframe width="407" height="277" src="https://www.youtube.com/embed/FfHyVVrBjWU" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe><br /><br />Yes, of course I knew the main point we wrote about the "axion weak gravity conjecture". That point – discussed in a paper by <a href="https://arxiv.org/abs/hep-th/0303252">Banks, Dine, Fox, and Gorbatov</a> (and in some lore I could have had heard from Tom many years earlier, unless I told him) – had largely stimulated the research into the "normal" weak gravity conjecture itself.<br /><br />The conjecture says that the decay constant of an axion shouldn't be too high – in fact, its product with the action of the relevant instanton is smaller than one in Planck units. This is a generalization of the "normal" weak gravity conjecture because the instanton is a lower-dimensional generalization of the charged massive point-like particles (higher-dimensional ones exist as well) and its action is a generalization of the mass/tension of the objects.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Our claim implies (the previous formulation by Banks et al.) that either the decay constant or the instanton action or both have to be small. And this condition has a nice implication: quantum gravity doesn't want to allow you to emulate flat potentials too closely, unless they're exactly flat, so the axion "wants" to be visible either because its decay constant is low or because the instanton corrections to its potential are sufficiently wiggly.<br /><br />This is one of the particular insights that indicates that string theory's predictivity always remains nonzero – string theory doesn't want you to approximate the effective field theory of one vacuum by another vacuum too closely.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />In the older Banks et al. formulation, the "axion weak gravity conjecture" was considered as a bad news because it indicated that some natural attempts to construct natural inflation were actually forbidden in quantum gravity.<br /><br />Fine, now the two Dutchpersons look at a sufficiently wide and rich class of string compactifications to test the "axion weak gravity conjecture" – at type IIA string theory vacua on Calabi-Yau compactifications. Note that type IIB has the "point-like in spacetime" instanton, the D(-1)-instanton, and similarly all the other odd ones. The Dutch paper looks at type IIA so they need to look at the even D-brane instantons.<br /><br /><img src="https://lh3.ggpht.com/lubos.motl/SNzHOSzB_JI/AAAAAAAABCo/hQHOSzwUfcY/animated-quartic.gif" width=407><br /><br />OK, the "generic" Calabi-Yau has everything of order one. To make the decay constants and instanton actions parameterically large or small, so that you may study whether some inequalities are parameterically obeyed or violated, they need to study extreme shapes of Calabi-Yaus. They look at extreme corners of the complex structure moduli space. The analysis of these "extreme directions" is somewhat analogous to my and Banks' <a href="https://motls.blogspot.com/2009/02/dualities-vs-singularities.html?m=1">dualities vs singularities</a>.<br /><br />And indeed, for every extreme direction in the Calabi-Yau complex structure moduli space, they find a tower of the D2-brane instantons that is predicted by the "axion weak gravity conjecture" – with the parameterically correct actions. That's quite a nice test of the conjecture. Curiously enough, to argue that the instantons exist, they need to use another swampland conjecture, the "swampland distance conjecture". Because the weak gravity conjectures should be counted as "swampland conjectures", they use one swampland conjecture to complete the partial proof of another one. I guess that a "swampland skeptic" could remain skeptical and call the proof circular.<br /><br /><iframe width="407" height="277" src="https://www.youtube.com/embed/MXXRHpVed3M" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe><br /><br /><em>OK, Vengaboys are Dutch, too.</em><br /><br />At any rate, the "axion weak gravity conjecture" has passed a test (at least assuming that other conjectures hold) and it looks like a nontrivial test because the limits in the space of shapes of a Calabi-Yau aren't quite simple. The authors of the weak gravity conjectures arguably weren't idiots, it seems once again. The situation is really provoking because the weak gravity conjectures may be motivated and formulated rather easily and have a "philosophical beauty, naturalness, and coherence" which are very important in theoretical physics. <br /><br />On the other hand, the proofs are partial, context-dependent, and very technical.<br /><br />Cannot there be a universal proof of the "weak gravity conjecture(s)" that really unifies and clarifies all the partial proofs and that is as straightforward as the proof of Heisenberg's\[<br /><br />\Delta x \cdot \Delta p \geq \frac{\hbar}{2}<br /><br />\] or the generalized uncertainty principle inequalities? And don't these weak gravity conjectures have some direct far-reaching philosophical consequences for quantum gravity – much like the uncertainty principle basically implies that probabilities must be predicted relatively to an observer and from complex amplitudes?<br /><br />Well, let me give you another, more detailed hint what you need to do to make a breakthrough analogous to the quantum mechanical one. In quantum mechanics, you first needed to realize that \(x,p\) from the inequality should be replaced with Hermitian operators. Here, we are talking about the values of parameters in <em>effective actions</em> of quantum gravity. So these parameters that enter the WGC-like conjectures must correspond to <em>some objects</em>, let's call them <em>prdelators</em> because they're like operators but probably not quite, constructed within the full theory of quantum gravity or string/M-theory (which is more abstract than just an effective field theory). Your main task is to figure out what a "prdelator" is and why it has the property analogous to noncommutativity that is responsible for the swampland inequalities. And Czech readers must be warned that their partial understanding could be illusory.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-75611575873680162822019-05-04T10:14:00.000+02:002019-05-04T16:50:17.312+02:00Farmelo's interview with WittenLast year, physicists' (especially Dirac's) biographer <a href="https://grahamfarmelo.com/the-universe-speaks-in-numbers-interview-5/">Graham Farmelo interviewed Edward Witten</a>. (Hat tip: John Preskill, Twitter.) If you have 27 spare minutes, it's here.<br /><br /><audio class="wp-audio-shortcode" id="audio-2327-1" preload="none" style="width: 100%;" controls="controls"><source type="audio/mpeg" src="https://grahamfarmelo.com/wp-content/uploads/2019/04/USIN-Pod_Ep5_EdwardWitten_Final.mp3?_=1" /><a href="https://grahamfarmelo.com/wp-content/uploads/2019/04/USIN-Pod_Ep5_EdwardWitten_Final.mp3">https://grahamfarmelo.com/wp-content/uploads/2019/04/USIN-Pod_Ep5_EdwardWitten_Final.mp3</a></audio><br /><br />Farmelo speaks like an excellent host – the framing, background music, and intonation seem professional for someone who is mostly known as a writer. OK, Witten was relaxed and said he was interested in astronomy as a kid. Many kids were – there were astronauts and other things at that time. Witten mastered calculus at the age of ten or eleven (depending on the type IIA coupling constant – and yes, he is an M-theory guy with a high coupling LOL), it's a bit later than your humble correspondent, but OK. He couldn't quite hide that his mathematician father had something to do with this mathematical exposure.<br /><br /><img src="https://www.nsf.gov/news/special_reports/medalofscience50/images/witten_1.jpg"><br /><br />He was interested in other things, worked on a failed Democrat Party candidate's presidential campaign (the victorious president above brought more smile to both men!), and realized physics was his cup of tea after the age of 20.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />I was a bit surprised to hear that his first professional-level exposure was to physics, not mathematics. Intuitively, Witten just looks like a man whose formative years were shaped by mathematics, not physics, but it's apparently an illusion. He was only dragged to deep mathematical aspects and mathematicians' mathematics later.<br /><br />(OK, I verified with Wikipedia and I insist that I am not completely wrong. After an economics graduate school, Witten joined as an applied mathematics graduate student, and switched to physics only later, earning PhD under Gross in 1976. Applied mathematics grad school, father-mathematician... I just don't buy it's completely wrong to say that Witten the kid hasn't been shaped as a mathematician.)<br /><br />Witten talked about the fast pace of experimental discoveries a few decades ago. When he became a graduate student, the pace slowed down considerably. So I guess he rationally figured out that he had to work more theoretically to optimize the output. <br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Witten mentioned some interactions with Steven Weinberg – who had some fun while explaining current algebras to the current algebra infidels that included Witten. Sidney Coleman was important for Witten – the only guy who was really interested in strongly coupled QFTs (and instantons etc.). OK, Witten was probably the second guy. Michael Atiyah, Saša Polyakov, and Albert Schwartz are mentioned in connection with Witten's interest in instantons. (Georgi and Glashow are mentioned as weak-scale phenomenologists.)<br /><br />That's where Witten probably got his mathematical edge – he learned sheaf cohomology groups and stuff like that. "Sheaf cohomology group" sounds like more hardcore mathematics than your favorite hardcore server but for Witten, it was apparently a matter of "learning about the physical topic of instantons just a bit more deeply than the average physicist". Index theorems got to the game, Witten did some influential mathematics work there. Some Polyakov's instanton program hasn't worked for physics as expected but it turned out interesting in other, more mathematical contexts.<br /><br />Witten finally learned some Morse Theory while in swimming pool in Aspen, Colorado. Again, Witten does his best to deny he had any sort of mathematician's thinking. He was like other physicists who heard "Morse Theory" (or what it's good for) for the first time etc. He crisply explains the theory – as counting of the maxima, minima, and saddle points whose combination is determined by a topological invariant of the domain.<br /><br />Some basics of string theory and the 1984 First Superstring Revolution are discussed. The anomaly cancellation needed some mathematics that was known to mathematicians (and to a limited extent, to Penrose and perhaps a few others) but not to physics graduate students. String theory has obviously made difficult mathematics more important.<br /><br />The harmony between mathematics and physics is a "fact of life". He doesn't know what an "explanation of this harmony" would sound like, and neither do I. ;-) The very distinction between mathematics and physics depends on some slightly contrived definitions which introduce a conceptual boundary – and the relationship between them really means that you may remove the boundary that you just artificially added. What a big deal. ;-)<br /><br />At 17:00, Farmelo uses the term "string framework". For years, the classification as "framework" has actually been favored over "theory" by some people such as David Gross. The string framework is an "alternative" to the quantum field theory framework. Nice but there is still a difference: the QFT framework is composed of many theories/models while string theory really <em>is</em> a single theory. So the two "frameworks" aren't analogous in most key respects. <br /><br />Like your humble correspondent, Witten says that string/M-theory is the <em>only interesting</em> direction to go beyond the well-established framework of quantum field theory. A year ago or two, an article in The Quanta Magazine forced Witten to recant and an anti-string activist was able to force a deceitful edit of Witten's phrase to say that "string theory is one among many". But "it is revolving, anyway", Witten somewhat bravely reiterated, and string theory is indeed the only game in town in the absence of activists in the IAS dining hall or on the sofa in Witten's office (he was sitting at the point (0,0,0,0)).<br /><br />So Witten got some small positive points for bravery on this point. But if it remains in isolation, and if he's not facing those who find "it's the only game in town" politically incorrect, the points are really small. You have to try harder, Prof Witten, to get rid of the relatively cowardly image. OK, here he corrected Farmelo's statement about "other routes". "There aren't any other routes," Witten has informed Farmelo. And "loop quantum gravity"? It's just words. Exactly. String theory is the only interesting way to go forward. Loop quantum gravity is a triplet of words used for some spin networks – and these spin networks have rather clearly nothing to do with quantum or any gravity which is why the triplet of words is misleading.<br /><br />(Similarly, "asymptotically safe gravity" are just words. They could mean something but they surely don't mean a theory – not even a sketch of a theory – that has some well-defined rules and that has, according to some available evidence, a significant potential to solve some actual problems counted as "quantum gravity". The phrase "asymptotically safe gravity" represent some scale-invariant local QFT that is gravitational at the same moment. Because of holography and the black hole spectrum etc., it's unlikely that quantum gravity could be equivalent to a local or even scale-invariant quantum field theory in the bulk spacetime. I am pretty sure that Witten agrees with all these claims of mine about all the "alleged alternatives" to string theory.)<br /><br />Concerning the absence of post-Higgs LHC discoveries, Witten recalls the widespread belief that the Higgs physics would have come together with new physics that fixes the Higgs scale – as a very low scale in comparison with the Planck scale. The absence is "extremely shocking" to him. Well, I would surely use less dramatic words – the fine-tuning may still be 1-in-100 and I don't find events with a 1% probability "extremely shocking". For him, a huge surprise was also the positive (but tiny) cosmological constant. Witten used to feel a big discomfort with the landscape or multiverse but he is less upset about the multiverse now than a decade ago – the Universe's purpose is not to make him feel comfortable. Well said. When the daily wars about the multiverse are over, I totally calmly accept this general picture as a clear possibility.<br /><br />Some down-to-Earth questions may be solved in physics of the near future. The biggest new ideas may be completely unknown to everybody now. Among the known routes, the entanglement-geometry (spun as "it from bit") link seems most interesting to him now. Sensible in all counts. So the next upheaval could come from the entanglement-glue duality. Witten, usually too shy to forecast visions for the future (perhaps after some wrong predictions), regained some (totally reasonable amount of) composure and argued that his closet prophetic bones could have predicted such upheavals "a few years in advance" two or three decades ago – not bad. ;-) He should allow his prophetic bones to speak a little bit more often.<br /><br />Witten says that people with various opposing opinions about "new physics" were all a little bit wrong. Expectations of lots of new (experimentally found) physics were wrong but so were the ideas that it would mean that the progress would stop. The progress since his graduate school was cool enough – and it has enriched mathematics, condensed matter physics, and more.<br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=0465056652&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>Farmelo praised Witten for the precision of speech and avoidance of philosophically sounding verbal gibberish. At the end, aside from promotion of his books, Farmelo admits that a purpose of that interview was to fight against the myth that Witten is a mathematician self-framed as a physicist. I surely believe in this myth less than the actual believers (Witten is an amazing physicist – and a universal top phenomenologist, he learned much of SUSY phenomenology from Gordon Kane etc.) but I still believe it's somewhat true and the interview hasn't substantially reduced this partial belief of mine, sorry. ;-)<br /><br /><iframe width="407" height="277" src="https://www.youtube.com/embed/nMjXz5hKAR4" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe><br /><br />Totally off-topic. I had wanted to embed this animated history of Czechia's map (with Smetana's Vyšehrad/Upper_Castle, a part of My Country) sometime in 2019 – and it's 2019 now. <br /><br />If you find the years 1019-1041, you will see that Czechia's shape was almost identical to the Czech Republic as of today. In 1019, although it could have been 1029 as well and no one is sure, Duke Oldřich of Bohemia finally conquered Moravia, the Eastern 40% of Czechia that was organized as a margravate-not-kingdom throughout the feudal history.<br /><br />So within miles on all sides, Czechia has had the same shape for 1,000 years in this year. The territory firmly controlled by Prague has been larger at some moments and we used to have access both to the Baltic and Adriatic Sea – but it used to be smaller, too, like nothing LOL. We're probably the world's most territorially stable country of the last 1,000 years now, congratulations to us.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-82995968384419953742019-05-02T12:57:00.001+02:002019-05-02T17:16:40.554+02:00How string theory irreversibly changed our understanding of the physical lawsIn the previous text, I tried to focus on the <a href="https://motls.blogspot.com/2019/05/first-stringy-steps-how-young-fieldist.html?m=1">differences in the treatment of QFT</a> (quantum field theory) that may discourage too naive students of "mundane QFT" when they are trying to switch to modern advanced QFT and string theory in particular.<br /><br />This text is somewhat similar but it focuses on the "later differences" – what string theory actually tells us about the world and the physical laws that we didn't know when we were confined in the mundane QFT paradigm – or that we couldn't even imagine. There's some overlap with texts such as <a href="https://motls.blogspot.com/2006/06/top-twelve-results-of-string-theory.html?m=1">top 12 achievements of string theory</a> – Joe Polchinski had added the last two – but here I am looking at the issue from a different, less marketing and more heureka, perspective.<br /><br />So what do I see differently than when I was in the mundane QFT phase?<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Note that all these insights, and some others, show that it's childish when someone wants to "return" physics to a pre-stringy era. We – I really mean the body of the best theoretical physicists – have simply learned some things that cannot be "unlearned".<br /><br /><b>Theories that seemingly look different may actually be the same.</b><br /><br />I chose this as the #1 point not because I am sure it's the deepest one but because it's arguably the most self-evident and well-defined class of insights among the sufficiently important ones.<br /><br />In physics jargon, <em>dualities exist</em>. Dualities have become omnipresent in string theory – and in QFT. Only when physicists had several examples, they were pushed to qualitatively change their perspective. Before the discovery of dualities, physicists thought that if two theories differ in some technical aspects and if there's no "sufficiently obvious" field redefinition or a map that shows their equivalence (usually some kind of drudgery that brings a Lagrangian in one form to another form), the theories have to be physically unequivalent.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Before string theory, people knew various equivalences. Different formulae for a function – e.g. Riemann zeta function – were equal to each other. Great but in some sense "straightforward". Schrödinger's definition of quantum mechanics is equivalent to Heisenberg's or Dirac's one, when properly interpreted. That's also great but it boils down to a rather simple unitary transformation.<br /><br />But physicists used to assume that these equivalences only apply to "objects of limited size". When you describe the <em>laws of physics for a whole Universe and everything in it</em>, you have specified so much information that it just can't be equivalent to a completely different set of physical laws. But the equivalences actually exist everywhere.<br /><br />So we have the equivalence of sine-Gordon and the massive Thirring models; fermionization and bosonization. S-duality, T-duality, U-duality, string-string duality, M-theory – type IIA duality, mirror symmetry. And many more that I will discuss separately. Most of these dualities were first found in string theory and/or in QFT that is close to string theory, or at least in QFTs by string theorists i.e. physicists who have the ability to do research on string theory. <br /><br />We know that similar dualities, like S-duality of Yang-Mills, exist even in local QFTs. The lesson may be more general. Maybe if you find some other theories different from QFTs or string theory, they will also exhibit dualities. But string theory has been the playground where we actually learned this general lesson. Intelligent enough theories of Nature exhibit dualities.<br /><br />You shouldn't underestimate the philosophical importance of dualities. It really means that an "apparently different collection of basic building blocks and interactions" may be completely equivalent to a "seemingly completely different one". It means that our description of a theory – our way of thinking about the allowed objects and their evolution, their shape in the spacetime, and even the dimension of the spacetime etc. – "overdetermine" the actual physical identity of the theory. Our language – even when it's mathematical language – is too talkative. The physical beef of the Universe is just the language modulo some powerful equivalences and redundancies.<br /><br />Dualities are clearly important, even at the fundamental philosophical level, and those who keep on assuming that dualities don't exist are just wrong. They assume something that could have been natural to assume centuries ago. But we've learned that it's wrong – just like the Flat Earth is wrong – and the newer picture we have learned is actually more exciting. "The perfectly precise physical equivalence" between "two worlds" whose basic laws look qualitatively different – and aren't related by any obvious enough field redefinition – could have looked "infinitely unlikely" before string theory but we know that such things are omnipresent so they just can't be assumed to be infinitely unlikely!<br /><br />Some dualities are considered a great playground by pure mathematicians, such as mirror symmetry, but this blog post isn't about "achievements" but about "paradigm shifts in physics", so I won't dedicate special sections to the "ways how string theorists have impressed pure mathematicians" here.<br /><br /><b>In quantum gravity, the maximum information doesn't scale with the volume.</b><br /><br />It scales with the surface. The black hole entropy is proportional to the event horizon's surface. You just can't compress too much information at a fixed information density to excessively large regions. The black hole entropy was known to be proportional to the surface in the 1970s, before it was derived from string theory. But string theory has confirmed the formula and has added more explicit pictures, especially the AdS/CFT correspondence, that make it clear that at least in some contexts and descriptions, the information about the whole region in quantum gravity "lives on the surface" and looks rather local on the surface.<br /><br />To make it brief, string theory has been rather essential to realize – and make explicit – all the ideas that we call the holography of quantum gravity.<br /><br /><b>There's no qualitative difference between elementary particles and black hole microstates</b><br /><br />Black holes look like qualitatively different, large "beasts" that differ from the elementary particles. But string/M-theory has shown us that the black hole microstates – there are many microstates because the black hole entropy is large for a large black hole – are nothing else than the "very massive" counterparts of elementary particle species.<br /><br />The qualitative difference between an electron and a black hole could have looked – and arguably did look to most people – "obvious" but we already know it's wrong. Even if one found a theory of quantum gravity that is totally different from M-theory or type I/IIA/IIB or heterotic string theories, it would almost certainly be true that elementary particles, including the graviton, are just light siblings of the exponentially many black hole microstates describing heavy black holes.<br /><br />We have learned a lesson here. We know how to interpolate between particles and black holes in various examples. We will never return back. When we were mundane QFT theorists, we thought that a realistic theory of quantum gravity required us to make two objects – black holes and elementary particles – peacefully co-exist. We know it was wrong: there is no qualitative difference between the two and a promising theory produces both kinds of objects simultaneously, from the same underlying material and laws.<br /><br /><b>All dimensionless parameters are ultimately determined in quantum gravity, unless there are exactly massless scalar fields.</b><br /><br />The Standard Model has some 30 parameters, the MSSM has about 105. We got used to the parameters in mundane QFT. It looked like we could pick the spectrum and then we could also adjust the masses, mixing angles, and the renormalizable couplings, among a few others. And we also had the tendency to disfavor effective QFTs with many parameters – an Occam razor's instinct. But string/M-theory shows that it's wrong. The couplings are ultimately all determined in quantum gravity, and if they're not, there has to be a modulus, an exactly massless field that causes a new long-range "fifth force" and that violates the equivalence principle (so this possibility is heavily disfavored experimentally).<br /><br />So the "freedom" to adjust the parameters – which looked like the final answer in mundane QFT – is actually an illusion in quantum gravity. Perhaps because quantum gravity, like string/M-theory, must negotiate the peaceful co-existence between the black holes and the light elementary particles, it imposes new constraints and those imply that the allowed values of the dimensionless parameters are <em>discrete</em>.<br /><br />This change of thinking also means that it is utterly irrational to disfavor effective QFTs with a higher number of couplings. The number of couplings in a low-energy effective QFT is whatever it is predicted to be (and you should always allow all couplings that keep the symmetry, consistency, and degree of renormalizability of the theory!). 30 or 105 may look like many but it doesn't measure any "sickness" or "contrivedness" of the theory because these collections of parameters are derivable from a more fundamental viewpoint that in principle has no adjustable continuous parameters.<br /><br />Again, it's a paradigm shift that is almost certainly correct – moving us from a naive, wrong answer to the mature, correct one – and it's a paradigm shift that largely took place thanks to string theory. Even if you imagined that string theory will be superseded by a different one, it's very likely that the new one will in principle determine all the parameters, up to a discrete set of choices. Such string vacua or similar theories clearly do imply low-energy predictions, including the number of "seemingly free but not really free" parameters, and that's why all the people who are "repelled" by a higher number of parameters, or by one number or another, just don't understand the non-fundamental character of effective QFTs.<br /><br /><b>Topology of the spacetime manifold isn't a good observable.</b><br /><br />Before some string theory advances, people already knew that the spacetime was able to get curved – like in Einstein's general relativity. They did believe that in quantum gravity, it was right to imagine it as a "quantum foam" where the geometry oscillates and changes the topology. So many things may be hard. But they only talked the talk – they didn't walk the walk.<br /><br />Whenever they considered how gravity interacts with itself and other fields, they were actually <em>completely ignoring</em> these warnings that "topology in quantum gravity may be hard" etc. In particular, people were assuming that whatever quantum physics you discuss, you first need to determine some background spacetime's topology, and that gave you some subsectors of the Hilbert space. And in each Hilbert space, you could discuss various states that differed by the fields – and continuous deformations – on top of the fixed topological spacetime background.<br /><br />We know that this can't work. The "total Hilbert space" simply isn't neatly split to these "superselection sectors" separated according to the spacetime topology. In the Calabi-Yau topological transitions, we know that excitations of one topology may be said to be equivalent to other excitations of a "nearby topology". In the ER-EPR correspondence, a wormhole is equivalent to an entangled black hole pair. The two sides have different topologies but they correspond to the same states.<br /><br />So even the spacetime topology is a part of the description, a "way of thinking about some physical states", but if the two ways of thinking differ from one another, it doesn't mean that they're not the same states! So one can't uniquely associate topologies to a basis of the Hilbert space. One can't say what is the probability that a generic, chosen state of the Hilbert space has the spacetime topology X or Y. There are many possible answers to such a question. There's no general way to "measure" the spacetime topology, at least not for microscopic (Planckian) objects or highly entangled states.<br /><br />Also, the spacetime topology may "continuously" change by physical processes, in flop transitions and other critical transitions... A whole discussion of the "emergent character of spacetime" could be added here but I don't want to focus on that important point in this blog post. Again, the emergent nature of the spacetime has been a "lore" for some time but people didn't know how to deal with it mathematically. In string/M-theory, we have increasingly known how to convert the "emergent character of the space" into equations.<br /><br /><b>Supersymmetry is a rare fermionic symmetry allowed in physics</b><br /><br />In Russia, supersymmetry was basically discovered by "mathematicians" who studied some advanced "group theory". In the West, almost simultaneously, supersymmetry (the world sheet supersymmetry) was first discovered by Pierre Ramond when he worked to add fermions to the 2D string world sheet. After Ramond, simple 4D SUSY theories were built by Wess and Zumino. Supergravity theories etc. were added in the late 1970s, the MSSM has been studied since 1980 or so.<br /><br />Supersymmetry is a new kind of symmetry whose generators are Grassmannian. It is a "moral loophole" in the Coleman-Mandula theorem. Almost all string theorists' preferred models of the real Universe require supersymmetry. The alliance between string theory and supersymmetry is obvious, and so is the importance of string theory for the discovery of supersymmetry (at least in the West).<br /><br />Also, supersymmetry restricts the maximum dimension of the spacetime – basically because the dimension of the spinor-like representations, needed for fermions, grows exponentially with the dimension but it still has to match the degeneracy of the bosons. M-theory's 11 dimensions, and more subtle and debatable "12 dimensions" of F-theory, is about the maximum. I think that S-theory in 13 dimensions etc. are already extremely problematic and you just shouldn't assume that they're as physical and decompactified theories as M-theory. Even F-theory is already problematic but F-theory's usage for the construction of stringy vacua is a hard science that works (but two dimensions out of 12 are simply not quite decompactified in fully physical vacua, they are a torus). S-theory is not, so far.<br /><br /><b>Near the Planck scale, the idea of finitely many local fields is not OK.</b><br /><br />People sort of knew it from the beginning – if one studies quantum gravity, something prevents you from localizing objects and particles with a better precision than one Planck length or so. String theory makes these guesses quantitative in various ways. Particles can't be quite point-like, they are typically objects such as vibrating strings whose size cannot be smaller than the Planck length. Their internal fluctuations make it unavoidable that their limbs may fluctuate at least one Planck length away.<br /><br />Also, if you study all particle species at the Planck length resolution, you will find infinitely many, like infinitely many excited string modes. At a higher coupling, they're not quite independent because of ER-EPR and other things.<br /><br /><b>QFTs are ultimately not man-made, and they're connected within a natural theory and its "landscape".</b><br /><br />As I mentioned, in mundane QFTs, one thought that physics is an inventors' game. You pick your building blocks – particle species or fields – and their interactions. These are like different car models, separated from each other.<br /><br />String theory makes it clear that physicists are ultimately discovering, not inventing or constructing, effective QFTs. QFTs compatible with quantum gravity form a particular set that looked "unlimited" when people were in the naive mundane QFT stage. But now they have analyzed a lot of physics and we arguably know "a big chunk of the allowed effective QFTs". <br /><br />Their particle spectrum and the qualitative characteristics of the interactions aren't something you can really choose freely. For some choices, there may exist no vacuum of quantum gravity that allows the particle spectrum or some forms of the potentials and other interactions. Such QFTs forbidden within quantum gravity are referred to as the swampland.<br /><br />The allowed theories are actually created by Nature – they are solutions to some fundamental equations. They are long-distance limits of string/M-theoretical vacua. A theory with certain properties at low energies may exist or it may refuse to exist. The answer isn't up to you. There are deeper laws and the "man-made construction" of a QFT is just a "guess" how a limit could look like.<br /><br />In the mundane QFT phase, people were always "bottom-up model builders", assuming that they had the freedom to build the theory in any way. They actually <em>knew</em> that the low-energy laws were just <em>derived</em> from more fundamental ones – by taking the limit or by the RG flows. But as in other cases, they talked the talk but didn't walk the walk. Now we know that we have to walk the walk. We are really forbidden from considering some type of effective QFTs in quantum gravity.<br /><br />And some pairs or sets of QFTs may have looked equivalent at low energies – but they may still be limits of string vacua that differ at higher energies. The similarity or equality of two low-energy QFTs is therefore "an illusion", the underlying string vacua may be "very far from each other" according to some relevant measure at Planckian energies. People always knew that long distances were "derived" but they often thought as if the low-energy QFTs were "fundamental", anyway. We already know it is wrong to do so.<br /><br /><b>The choices of the QFT spectrum result from a geometric picture that should be looked for, that doesn't have to be unique, but the properties of that geometric picture may clarify special properties of the QFT.</b><br /><br />In mundane QFT, the particle spectrum was an arbitrary man-made input. In string theory, the spectrum is derived from the modes of strings and other buildings blocks that propagate and co-exist (with branes, fluxes etc.) in some higher-dimensional geometry.<br /><br />Even if we don't know what's the right stringy geometrization of our favorite QFT, like the Standard Model, we know that such pictures exist and they're almost certainly more fundamental. Also, they explain some special "accidents" in a QFT. For example, the decoupling of two sectors in a QFT may be due to the geometric separation of the excitations in the direction of extra dimensions, e.g. in a braneworld where the sectors arise from non-interacting brane stacks.<br /><br />You can still imagine that the choice of the fields and interactions is a "man-made process based on the human freedom" but you're simply not at the cutting edge of theoretical physics if it is so. If you keep on making this "man-made" assumption, you're like Kepler who identified the planets with Platonic bodies, assuming that such guesses could be right. But in our new stringy pictures, we really realize that random guesses like that have no a priori reasons to be right. Either you have some experimental evidence or it's just a silly unlikely guess. The likely guesses are those that may arise from a natural – complete or incomplete – UV-completion of the QFT, from a string compactification.<br /><br /><b>The choice of gauge symmetries isn't fundamental, either: gauge symmetries come and go and they're not real symmetries.</b><br /><br />In particular, the Standard Model starts with a choice of the \(SU(3)\times SU(2)\times U(1)\) gauge group. Like the spacetime topology, it's a "first choice" and everything else has to adapt it. In the new stringy picture, we know it's not the case. The gauge group is derived from the geometric properties of the compactification as well. And the choice of the gauge group isn't fundamental. After all, the gauge group isn't a real symmetry because physical states have to be invariant singlets.<br /><br />Heterotic string theory allows to interpolate between \(E_8\times E_8\times U(1)^2\) and \(SO(32)\times U(1)^2\), to mention a cool example. The groups have the same dimension and the same rank but they are clearly different. Just like we can gradually change the spacetime topology, we can deform the compact spacetime dimensions so that the relevant low-energy gauge group changes from one to another. Also, we know that the Yang-Mills gauge groups may be continuously connected to the diffeomorphism symmetry of GR – like in the Kaluza-Klein construction. But string theory gives us lots of new constructions that show the "sibling status" of Yang-Mills symmetries and general covariance. We actually know that these things, again thought to be rather separate choices in the past, are connected aspects of the same underlying substance.<br /><br /><b>Second quantization of fields isn't the only way to describe multi-particle states</b><br /><br />Relativistic quantum mechanics requires quantum fields and their creation and annihilation operators automatically allow antiparticles and multi-particle states. That was a great insight around 1930. In the mundane QFT stage, people thought it was the only way to get or describe the theories with multi-particle states.<br /><br />But we know it's not the only one now. In particular, matrix models allow the description of composite systems in terms of "block-diagonal matrices" in some theories whose degrees of freedom are large-size matrices. The BFSS paper is the simplest example of an equivalence between such a non-gravitational matrix model and something that should look like an effective QFT at long distances – namely 11D supergravity. The BFSS matrix model was the first full complete definition of M-theory at all energies.<br /><br />People could have always said that "the fundamental theory of our Universe doesn't have to be given by a strict QFT" but they didn't know how to reproduce all the realism and advantages of a QFT by a non-QFT, or something that explicitly avoids the "man-made construction of multiparticle states" by simply combining creation operators in a chain. Matrix models allow N-particle states to co-exist for many values of N.<br /><br />So we really know that the QFT apparatus isn't even needed to get multiparticle states in a relativistic theory – we have other descriptions that achieve the same goal without explicit chains of creation operators. The inevitability of QFT as a framework for the multi-particle states has decreased or disappeared.<br /><br /><b>Summary</b><br /><br />This list is surely not complete and some important entries are missing – and I will realize some of them in an hour from now. But there simply are entries like that which show that our assumptions about how we should proceed in QFTs, what is natural in QFTs, and whether QFTs are necessary at all were simply wrong – once you try to construct complete theories that incorporate quantum gravity. String theory has shown that lots of things previously considered impossible or extremely unlikely are actually possible if not omnipresent. Some unnatural things became possible. Other, previously possible things, are banned.<br /><br />So we know that to stick to the old picture means to be attached to something analogous to the medieval prejudices about science. There were vague reasons to believe those prejudices in the mundane QFT stage. But the research into string/M-theory has simply falsified them – much like the Flat Earth has been falsified. Our modern stringy proofs that settle these questions are much more reliable than the vague guesses that have led to the old answers – many of which are believed to be incorrect now. So if you're a competent theoretical high-energy physicist as of 2019, you simply need to know the modern answers obtained with some very explicit and indisputable evidence – and you have to abandon the prejudices that used to be justified by sloppy evidence and that have been proven wrong.<br /><br />The idea that physicists will "return" to an epoch in which string theory and its lessons may be ignored is as childish as the idea of a "return" to the Flat Earth. Science just doesn't work like that. Even in the absence of some "characteristically stringy empirical evidence", string theory has brought us proofs of many important, even philosophically game-changing statements that have falsified some incorrect hypotheses in the future.<br /><br />The falsification of those old expectations – and this falsification had the form of a nearly rigorous mathematical "disproof" – cannot be undone. Falsification can never be undone. And the fact that no actual new experimenters were needed for the advances changes nothing about the irreversibility of the disproofs whatsoever. So unless you undergo lobotomy or burn all books and web pages that carry the knowledge about string theory, it's just impossible to "unlearn" string theory. Everyone who suggests that top theoretical high-energy physicists of 2025 could work on something that denies the whole history and lessons of string theory are completely detached from any kind of rational thinking about science and you should never assume that they're "equivalent" to actual physicists because they are not.<br /><br />And that's the memo.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-73627374296053368262019-05-01T09:19:00.001+02:002019-05-01T13:30:59.719+02:00First stringy steps: how a young fieldist expands her mind to become a string theorist<b>And yes, "she" is probably but not necessarily a young man</b><br /><br /><a href="https://motls.blogspot.com/2019/04/string-theorists-approach-status-of.html?m=1">Three days ago</a>, I mentioned that a "string theorist" is a description of expertise that includes most of "quantum field theory" but it goes beyond it, too. Seeing the world in the stringy way opens new perspectives, new ways to look at everything, and unleashes new powerful tools to theoretically wrestle with all the world's scholarly problems.<br /><br /><img src="https://d35c7d8c.web.cern.ch/sites/d35c7d8c.web.cern.ch/files/bg_13.gif" width=407><br /><br />In practice, string theory isn't some philosophical superconstruction on top of quantum field theory (QFT) that is very different from the QFT foundations. Instead, string theory calculations are almost entirely identical to QFT calculations – but QFT calculations with new interpretations and new previously neglected effects. Most of the fundamental insights of string theory are irreversible, nearly mathematically rigorous insights about <em>previously neglected properties and abilities of QFTs</em> and especially previously overlooked properties of some special QFTs.<br /><br />What are the limitations of a QFT student that prevent her from seeing physics through the new, stringy eyes? Let me look at these matters a little bit technically.<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />OK, let's first review the QFT. The Standard Model is the most "practical yet comprehensive" QFT relevant for the experiments that are actually being made. All the details are technical and only roughly 100,000+ people in the world understand them well enough. But the "verbal summary" is rather concise.<br /><br />QFT is a special kind of quantum mechanics (QM). So we calculate probabilities of possible outcomes of observations. These probabilities are computed as the squared absolute values of the complex probability amplitudes – some matrix elements of linear operators on a complex Hilbert space.<br /><br />In practice, in QFTs, those are computed as sums of the Feynman diagrams, such as one at the top. The internal lines are "propagators", linked to the two-point functions of quantum fields (and to the bilinear terms in the Lagrangian) and representing "virtual particles" that are seen neither in the initial state nor in the final one. The vertices come from higher-than-linear terms in the Lagrangian and they are needed for all interactions.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />These Feynman rules – probability amplitudes are sums of Feynman diagrams – are derived either from some Dyson-like operator approach or from the Feynman sum over histories, the path integral. Each Feynman diagram translates to an integral – over locations of the vertices in the spacetime or over momenta of the propagators. <br /><br />In the Standard Model or any particular QFT, there is a spectrum of possible propagators. They correspond to spin 0 or 1/2 or 1 particles in the Lagrangian. Some of them are gauge fields, you learn about the gauge symmetry, and if you're a bit advanced, you really master the renormalization, renormalization group, and non-perturbative effects such as instantons, among a few other things. I wanted to be really concise – so that's it. You must only understand that these several simple paragraphs translate to some 1,000 pages from textbooks if you really want to understand what my words mean – so that you can use the QFT apparatus! ;-)<br /><br /><b>Now, what are the new objects or treatments that string theory adds? How do you upgrade yourself from "one of the 100,000" QFT experts to "one of the 2,000" more or less string theorists?</b><br /><br /><iframe align="left" scrolling="no" frameborder="0" style="width:140px;height:245px;" marginheight="0" src="//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=lubosmotlsref-20&marketplace=amazon®ion=US&placement=0000000000&asins=0521672279&show_border=false&link_opens_in_new_window=false&price_color=BBBBBB&title_color=FFAA44&bg_color=002211" marginwidth="0"/></iframe>Open a basic textbook on string theory such as Polchinski's book. I could only <a href="https://books.google.com/books?id=jbM3t_usmX0C&printsec=frontcover&hl=cs&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false" rel="nofollow">open Volume I</a> of Polchinski because Nima Arkani-Hamed has borrowed my Volume II, I think, and he hasn't returned it yet. ;-) Already the initial chapters and sections of the textbook bombard the reader with great new insights that are spiritually "beyond" the mundane QFT apparatus sketched enough – apparatus optimized for the scattering amplitudes in the Standard Model. But I want to present the novelties independently.<br /><br />The first novelty is that there are scale-invariant, conformal field theories (CFTs) and they have some special characteristics and allow new constructions and objects.<br /><br />In the primitive QFT as sketched above, it doesn't matter much whether a particle is massive. A propagator may contain an extra \(-m^2\) or not. It's not a big deal. Gauge bosons and gravitons really have to be massless at the fundamental level – well, gauge bosons may get masses through the Higgs mechanism – but the calculational framework isn't affected much. At most, the massless particles are a pain in the buttocks because they may add long distance, infrared divergences and related problems.<br /><br />In CFTs, massless particles aren't a liability. They are a virtue if not a necessity. Well, CFTs don't really allow massive elementary particles because those carry a special mass scale \(m\) and the corresponding special distance scale \(1/m\) which would destroy the scale invariance of the theory. Theories with massless particles are the beef of any CFT research. And CFTs bring new spacetime symmetries beyond the Poincaré group of translations, rotations, and boosts: the scaling and conformal symmetries.<br /><br /><img src="https://inspirehep.net/record/939745/files/cylinder.png" width=407><br /><br />In the \(d\)-dimensional spacetime where one of the dimensions is time, the Lorentz group is \(SO(d-1,1)\), isn't it? The conformal group is \(SO(d,2)\), I added one temporal and one spatial dimension. Relatively to the smaller Lorentz group, we have the extra \(J_{+-}\) that generates the scaling, \(J_{+i}\) that generates the usual translations, and \(J_{-i}\) that generates special conformal transformations. In two spacetime dimensions, there is an exception: the conformal group is infinite-dimensional, at least locally: any holomorphic function of the complex variable \(z\) preserves the angle at every point of the plane (we are talking about the Euclideanized spacetime or world sheet – the relationships to the Minkowski-signature ones is obtained by a Wick rotation or a similar analytical continuation). This is what you learn in the complex analysis – a mathematics course – as an undergraduate. Now, the action is invariant under these conformal transformations.<br /><br />For example, an infinite cylinder is equivalent to the plane with the origin removed – the exponential map \(z=\exp(-iw)\) is how you do it, the situation is clarified by the picture. So the insertion of some operator at the point \(z=0\) is equivalent to the information about the state inserted to the evolution of the infinite cylinder at \(w\to -i\infty\). Quite generally, in CFT, you do want to study operators inserted at particular points, including very complicated operators, and the behavior of the theory when two or many such operators are inserted somewhere.<br /><br />This is new relatively to the mundane QFT at the top. The mundane QFT really tells you that you should better not insert too many operators to several points, especially not nearby points, because that's a way to get ultraviolet (UV) divergences, i.e. short distance divergences, and those are a liability. But in CFTs which don't care about scales, there's nothing wrong about short distance and UV (just like there's nothing wrong about the IR) because all distances are physically equivalent by the scaling symmetry. So in fact, you do want to play with correlators of operators that are very close to each other. These correlators encode – in a new way – all the physical information about the interactions at the "finite" distances.<br /><br />CFTs are generally important in QFT – they're the "fixed points" of the renormalization group, and therefore an essential starting point to understand the set of all QFTs according to the renormalization group paradigm. But CFTs are also vitally important in string theory. While the mundane QFT doesn't tell you anything about CFTs, as an upgraded QFTist or string theorist you must be ready to probe special properties of QFTs with massless particles and scale invariance and new constructions that are only possible when the conformal symmetry works.<br /><br />In string theory, CFTs are important in the AdS/CFT realization of holography – CFTs on boundaries of the anti de Sitter space are equivalent to the full quantum gravitational (string/M) theory in the AdS bulk. But 2D CFTs are also the defining theories of any perturbative string theory – whose predictions are always calculated from the appropriate world sheet CFT.<br /><br />You need to recall what you should have learned when you studied the holomorphic maps. How do you write down a complex holomorphic function that maps one region of the complex plane to another? You may need many of these things, especially the most elementary ones such as the exponential, logarithm, and the rational function \(z'=(az+b)/(cz+d)\).<br /><br /><b>State-operator correspondence</b><br /><br />You should understand why the spectrum of "states on a closed string" is the same as the spectrum of "operators inserted at \(z=0\)". It has to be so because the states or the operators are needed to clarify what's happening at \(z=0\) i.e. \(w\to -i\infty\) and the rest of the 2D spacetime, the plane or the cylinder, is equivalent through the conformal transformation.<br /><br />This correspondence, SOC, is the only good thing in the Universe that starts with "soc", the rest is some social, societal, and socialist junk.<br /><br /><b>New important spacetime symmetries</b><br /><br />You need to learn the basic mathematics of the conformal symmetries. Why are the angle-preserving transformations isomorphic to a Lorentz group in a higher-dimensional spacetime? How do these maps work? What about the spherical inversion? Why is the CFT invariant under the spherical inversion?<br /><br /><b>Shocking new equivalences: bosonization and fermionization</b><br /><br />Especially when the masses are zero, and you deal with CFTs, there are some new equivalences between theories that would sound impossible from the mundane QFT viewpoint. One of them is the equivalence of bosons and fermions. In QFT, you think that the Fock space built from a bosonic field is totally different from the fermionic Fock space. It's different from a pair of fermionic Fock spaces, too (OK, by the pair, I really meant the tensor product of two fermionic Fock spaces, sorry). If the occupation numbers are any non-negative integers, it must be a totally different spectrum than the spectrum of a theory where the occupation numbers are either zero or one, right?<br /><br />In CFTs, this "obvious" conclusion is wrong. In fact, a free boson is equivalent to two free fermions. Some generalizations of this statement exist for interacting bosons and fermions, too. A boson with a sine self-interaction is equivalent to fermions with a quartic interaction in \(d=2\) CFTs. How is it possible?<br /><br />I believe that it's a good idea for a "mundane QFTist who is just upgrading herself to a string theorist" to verify this equivalent up to the extent that convinces her that something really works here – or perhaps more rigorously than that. One check is to count the degeneracies of excited states on an open or closed string. Two fermions may lead to the same degeneracies at each level as a free boson, assuming the corresponding matching choice of boundary conditions in both theories.<br /><br />Another one – which is equivalent to the counting of the states above – is through operators. The fermions may be defined as exponentials:\[<br /><br />\psi = \exp(i\phi), \quad \bar\psi = \exp(-i\phi)<br /><br />\] Well, there should also be some "ordering" sign, \(:\exp(\dots):\), which you need to master once you study these things really seriously. The exponential mapping between operators may sound very strange from a mundane QFT viewpoint but it's natural in CFTs. The bosonic fields \(\phi\) may be viewed as "generators of some operations" so if you exponentiate them, you may get a finite operation which may be equivalent to the insertion or destruction of a fermion. In effect, the exponential of the bosonic field creates a "kink", a discontinuity that can't be combined with another copy of the same discontinuity, so it ends up having the Fermi statistics (Pauli's exclusion principle).<br /><br />The inverse relationship is bilinear, of the form \(\phi\sim \bar \psi \cdot \psi\), because you need to cancel the charges of the fermionic fields. The current for this \(U(1)\) charge is \(\partial\phi=\bar\psi\partial \psi\). You need to study this equivalence – bosonization or fermionization – to be sure that the mundane QFT viewpoint prevented you from seeing some relationships that are clearly true and almost certainly important.<br /><br /><b>Operator product expansions (OPEs)</b><br /><br />The mundane QFT apparatus allows you to think in terms of "states" most of the time, like the people who think that QM is about states and not operators. However, the advanced QFT or string theory really forces you to admit that actual physics is about operators. So for example, in a QFT textbook, you could have learned about the anomalous dimensions of operators. But you didn't care – you didn't need such stuff for the computation of scattering amplitudes which seemingly included "all the interesting physics".<br /><br />In CFT, you need anomalous dimensions of operators. In mundane QFTs, the anomalous dimensions start with terms proportional to \(g^2\) etc., the squared coupling constant (that's also how the couplings "run" etc.). In CFTs, the anomalous dimensions may be "non-adjustable", fractional numbers such as \(1/16\). It's all very exciting. You may see interesting, both free or interacting, CFTs that can't be understood as deformations of a free QFT with an interaction that has a coupling constant. Instead, the coupling constant seems to be "fixed". Even for the free fermion, the spin field that creates a special point making the fermion antiperiodic around the location of the spin field insertion happens to have the dimension of \(\Delta=1/16\). You couldn't have constructed fields of dimensions \(1/16\) in the mundane QFT, could you? All dimensions were integer multiples of \(1/2\). You thought that only "de facto polynomial" functions of the fields and their derivatives were possible and more complex dimensions were impossible for that reason. But that conclusion was premature.<br /><br />So you need to learn what happens when two operators are inserted next to each other. There is some singularity. You know that the commutator of two operators \(F(\vec x)\) and \(G(\vec y)\) in mundane QFTs may produce a delta-function. But the simple product is harder – and the leading term when \(|\vec x-\vec y| \to 0\) is encoded in some Green's functions. In CFT, you need to focus on these things from advanced chapters of QFT textbooks that looked as "useless complications".<br /><br />The insertion of the two operators at points \(\vec z\) and \(0\) may be replaced by the insertion of one operator at \(\vec z =0\). You may expand this new operator in some power series in \(\vec z\). The leading terms are the singularities, usually \(c\)-numbers, that may be extracted from the Green's functions. These OPEs end up being important because they encode the transformation of operators under various symmetries generated by other operators, stringy scattering amplitudes in some limits, and more.<br /><br /><b>Monodromies: operators orbiting each other</b><br /><br />I mentioned many new things about QFTs that emerge when you study CFTs in any dimension. But the stringy world sheet has \(d=2\) where many new things occur. In particular, in a plane, a point may orbit another point and this is a topologically non-trivial operation. One may generate a phase or something nontrivial when one operator completes a full orbit around another.<br /><br />You need to understand how these operations may be linked to boundary conditions on a closed string. You need to understand that the situation in which the orbiting does "nothing" is special, we say that the operators are mutually local. And you need to learn how to calculate such things not only for the "basic" operators such as \(\phi,\psi,\bar\psi\) I mentioned above; but also for operators such as \(\exp(a\phi)\).<br /><br />Quite generally, the calculations involving the operator \(\exp(a\phi)\) where \(a\) is a number and \(\phi\) is a bosonic field are very important in CFTs. That's another fact that would look shocking from a mundane QFT viewpoint – that viewpoint only "encouraged" you to consider polynomial operators made of the basic fields. But I mentioned that these exponential operators with a particular value of \(a\) – well, there should have been \(1/2\) in my bosonization exponents, I can tell you now, at least in the normal conventions – are important for bosonization and fermionization. <br /><br />But these operators are needed to define string states with a generic momentum, too. You should learn how to compute their anomalous dimensions which scales like \(a^2\) and is related to the mass of the string. You should learn how to orbit these operators around each other, and more. There was nothing special about "exponential of fields" in the mundane QFTs but these objects are important and omnipresent in CFTs and string theory that uses world sheet CFT.<br /><br /><b>Virasoro algebra</b><br /><br />It is an infinite-dimensional Lie algebra generating all the reparameterizations of a circle, a periodic \(\sigma\) variable. It's generated by \(L_m\) and the commutator is \[<br /><br />[L_m,L_n] = (m-n) L_{m+n}<br /><br />\] in the simplest case. You should understand how it works, perhaps learn the central charge extension of the algebra as well, and basics of how to look for its representations. It is important because this algebra is a residual symmetry on the world sheet. It plays a similar role as the Yang-Mills symmetry or diffeomorphism symmetry (of GR) in the spacetime. On the other hand, the unphysical states of the Virasoro symmetry on the world sheet may be <em>matched</em> to the unphysical states in the spacetime – due to the Yang-Mills and diff symmetries. The world sheet gauge symmetry principles "produce" all the spacetime gauge symmetries that you need.<br /><br />There are less and more rigorous ways to deal with the Virasoro algebra, the BRST treatment is a modern advanced one.<br /><br /><b>Topologies of world sheets, cohomology etc.</b><br /><br />The higher-order string scattering amplitudes may be written as path integrals over world sheets of harder topologies – pants-like diagrams where strings merge and split, a sort of thickened versions of Feynman diagrams. Up to conformal transformations, the moduli spaces of possible shapes of such higher-genus Riemann surfaces are finite-dimensional. You should understand what the dimensions are, why they're finite at all, how the moduli spaces roughly look, and understand something about why the unitary S-matrix in string theory requires you to integrate over the moduli spaces in the most natural way, and what the most natural way is.<br /><br />The genus \(h\) topologies have some non-contractible loops. This is a kind of "topology 101" – and algebraic geometry – that you may need to analyze spacetime (compactification spaces), too. Homology, cohomology, their relationships with forms and cycles matter.<br /><br /><b>CFT on sphere, torus, and other important low-genus topologies</b><br /><br />The world sheet is normally considered compact – because all the infinite cylinders corresponding to the external particles may be "shrunk" and conformally mapped to disks. You should know the moduli space of such low-genus diagrams, with and without extra operator insertions. For the sphere, which is conformally equivalent to a plane by a stereographic projection, you need to see the Mobius \((az+b)/(cz+d)\) transformations.<br /><br />A half-plane is a \(\ZZ_2\) quotient of the plane, the \(\ZZ_2\) is generated by the complex conjugation of \(z\).<br /><br />But the torus is a "one-loop" diagram and has some special mathematics. A torus is a plane modulo a 2D lattice. The lattices that produce the same tori are equivalent via the \(SL(2,\ZZ)\), the modular group. The 2D torus may be read as a spacetime diagram in two different ways: the Euclideanized time is either the vertical or the horizontal direction. This gives you an equality between two different partition sums for different, basically inverse, temperatures! You should roughly know why it works – and then how it works precisely.<br /><br />At the mathematical level, you have a great opportunity to learn the modular forms, eta and theta functions, and similar stuff to express these partition sums and their symmetry properties (under the modular group in particular).<br /><br /><b>T-dualities and other equivalences</b><br /><br />The T-duality is a reparametrization of the fields on the world sheet that is somewhat analogous to the fermionization and bosonization but the basic form only requires bosonic fields. There's a way to switch from a bosonic field \(X\) to the T-dual field \(\tilde X\) on the world sheet. What actually happens is that \(X\) may be split into the left-moving and right-moving part (or the holomorphic and antiholomorphic modes, if you use the Euclideanized world sheet). <br /><br />And the T-duality is the reflection \(X_L \to -X_L\) that "mirror reflects" the spacetime coordinate \(X\), a field describing the embedding of the world sheet into the spacetime, but the T-duality only reflects the left-moving part of \(X\) while the right-moving one is conservatively kept fixed! (Or vice versa, but physicists' conventions admit that it's more natural for the right-movers and right-wingers to be conservative.)<br /><br />If you already know how string theory amplitudes are extracted from the 2D world sheet CFT, you will realize that this implies the equivalence of string theory on two totally different spacetimes.<br /><br /><b>Derivation of Einstein's equations and other spacetime effective equations</b><br /><br />2D CFTs are rather rare. They include the free bosons, free fermions – with lots of equivalences between the two – then things like the Ising models and minimal models. The latter are basically "countable", there is a spectrum of "exceptions" that still manage to be CFTs.<br /><br />But there are also CFTs with lots of parameters. The non-linear sigma model is the most important master example. The kinetic term \(\partial_\alpha X^\mu \partial^\alpha X_\mu\) in the world sheet Lagrangian is generalized by its being multiplied and contracted with a general function of \(X\),\[<br /><br />g_{\mu\nu}(X^\gamma)\cdot \partial_\alpha X^\mu \partial^\alpha X^\nu<br /><br />\] So all the values of the function \(g_{\mu\nu}\), for every value (point in spacetime) \(X^\gamma\) of the argument and for every choice of spacetime vector indices \(\mu,\nu\), is adjustable. It's exactly the information that defines a metric tensor field in the spacetime. Great. For every spacetime geometry, you may write down a theory for strings propagating on that spacetime.<br /><br />This theory looks conformal for every choice of the tensor. However, there are quantum effects that also violate the scale invariance in general. In particular, for each point \(X^\gamma\) and each choice of \(\mu,\nu\), the coupling constant \(g_{\mu\nu}\) has its \(\beta\)-function encoding its "running with scale", and that \(\beta\)-function has to vanish for the world sheet theory to be actually scale-invariant at the quantum level.<br /><br />And the cancellation of these "anomalies" actually tells you that the spacetime metric tensor must obey Einstein's equations! The \(\beta\)-function for the coupling \(g_{\mu\nu}(X^\gamma)\) ends up being basically the Ricci tensor at the same point, \(R_{\mu\nu}(X^\gamma)\). Its vanishing requires the Ricci flatness i.e. Einstein's equations in the vacuum. You may derive the defining equations of general relativity just from the requirement that the "conformal" strings may propagate on that spacetime!<br /><br />This is true for all other effective field equations in the spacetime. If open or closed string modes produce gluons or electrons, their Yang-Mills or Dirac equations may be deduced from the conformal invariance of the world sheet theory at the quantum level! The right hand side of Einstein's equations (and all other spacetime equations) also correctly emerges if you calculate other contributions to the \(\beta\)-function.<br /><br /><b>Lots of extra technicalities</b><br /><br />Weyl and diffeomorphism symmetry of the world sheet dynamics, fixed into the conformal symmetry, \(bc\) ghosts needed for that. Closed and open strings, various boundary conditions, how it affects both the states and the operators (open string vertex operators live on the boundary of open world sheets). Orbifolds and how their consistency requires something to work for the toroidal world sheets (modular invariance I mentioned). D-branes and how T-duality changes the dimension of the locus where open strings end. How the D-branes carry new fields. Why their dynamics is often Yang-Mills like. Addition of fermions to the world sheet, superstrings. Unorientable strings, orientifolds, and world sheet diagrams that are the projective sphere, Möbius strip, and Klein bottle – all those may be obtained from the sphere and the torus. And infinitely many harder topologies with boundaries and crosscaps.<br /><br />And of course the critical dimension. Why the scale invariance of the world sheet theory at the quantum level implies \(D=26\) for bosonic string theory and \(D=10\) for the superstring. Polchinski calculates \(D=26\) in seven different ways, to assure a sensible reader that there's some "deep truth" about that result.<br /><br /><b>Summary</b><br /><br />There are lots of wonderful insights about QFTs that happen to be CFTs – and especially CFTs in \(d=2\) which is appropriate for a string world sheet. These things can't ever <em>disappear from physics again</em> because they're really <em>established mathematical facts</em> about some classes of QFTs. If and when you study these things, and if you're intelligent, you will realize that it has been silly for you to be ignorant about them. You will know that they cannot be ignored. To "ban them" would be about as weird as banning molecular or nuclear physics or condensed matter physics (e.g. crystal lattices) for someone who has just mastered atomic physics.<br /><br />Lots of special identities hold in CFTs or \(d=2\) CFTs and lots of new consistent objects may be defined and many consistent operations may be performed. There's a way to define a unitary S-matrix for states in the spacetime that looks just like one from an "advanced QFT" but also includes consistent quantum gravity. All these things look at least as natural as those in spacetime QFTs – but the gravity is added on top of that.<br /><br />You will encounter some old objects – anomalous dimensions etc. – more often than in mundane QFT. You will learn some new functions, gamma functions for the tree-level amplitudes; eta and theta functions and modular forms for the toroidal partition sums and correlators. You will deal with some previously "unnatural" operators such as exponentials of bosonic fields. You will often treat the left-moving and right-moving (or holomorphic and antiholomorphic) parts of the fields separately, something that is impossible in \(d\gt 2\). Mundane QFT was telling you that "you shouldn't do certain things" but many of these things are extremely important, useful, and lead to new deep insights.<br /><br />Already at the level of perturbative string theory, basically Volume I of Polchinski, you will see that too many things seem to work. The amount of great surprises and unbelievable consistency gets even more formidable once you study non-perturbative string theory, S-dualities, string-string duality, maps between D-branes and black \(p\)-branes, once you can microscopically calculate black hole entropy, geometerize the gauge symmetries in many new ways, find many more dualities (unexpected equivalences between vacua of string theory or QFTs), and more. The existence of string/M-theory "explains" all these particular coincidences and equivalences as well as other unexpectedly constrained yet consistent constructions – and it also "happens" to be a theory that is capable of producing all the predictions as the QFT class (plus consistent quantum gravity amplitudes).<br /><br />At some psychological level, the transition from "one in 100,000 QFTists" to "one in 2,000 string theorists" in the world starts by realizing that the mundane QFT picture is not the whole story. It hides many wonderful, mathematically natural things that may be done with quantum fields and many of their properties. It hides many special QFTs, like CFTs or supersymmetric QFTs or CFTs, and even more special kinds of those, that have even more striking properties. You will only make the transition from a "quantum field theorist" to "string theorist" if you have the sufficient curiosity and desire to understand how "things really work"; and sufficient intelligence – so that you know that you haven't run out of your mental capacity once you got to the mundane QFT level.<br /><br />Academically speaking, you don't need to be "certain" that string theory correctly describes our real Universe at a much better accuracy than any spacetime QFT. But if you actually master this material, so that you could get an A or B from most of the exercises e.g. in Polchinski's book, you will surely agree that it's utterly idiotic to <em>ignore</em> the existence of string theory or pretend that theoretical high-energy physics may continue or should continue while carefully <em>avoiding</em> all these stringy and similar (or similarly advanced) insights, constructions, and coincidences (that aren't quite "coincidental" because they're really "explained" by the existence of a unifying, deeper theory that unifies them all, string theory).<br /><br />String theory is more than the mundane QFT but they are tightly connected and inseparable. They form one continuum of insights – one may be more or less familiar with that continuum but there exists no meaningful framework that could present "less familiar" as an advantage. You clearly become a better expert in the properties of QFTs once you master at least basics of string theory.<br /><br /><hr><br /><iframe width="407" height="277" src="https://www.youtube.com/embed/NSYn8QArAD4" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe><br /><br />The left-wing establishment has restored propaganda, censorship, politically motivated dismissals etc. but they haven't revived the tradition of huge May Day parades yet. Check what the May 1st 1986 rally in Prague, five days after Chernobyl, looked like. Included are kids who are there for the first time, excited black students of biochemistry, history's criminals such as Marx, Engels, Lenin, and Gottwald, as well as the glorious Czechoslovak leaders of the mid 1980s. At the beginning of the march, you might have met the workers from the technological Tesla factory – some things aren't changing at all. I remember that such parades looked rather high-tech to me, at least in Pilsen, but when I watch this video, it is embarrassingly low-tech.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0tag:blogger.com,1999:blog-8666091.post-88955969585124070352019-04-28T09:38:00.001+02:002019-04-28T21:35:36.262+02:00String theorists approach the status of heliocentric heretics<a href="https://en.wikipedia.org/wiki/Galileo_affair">Galileo Galilei was legally harassed</a> between 1610 and 1633. Most of us agree that the Inquisition was composed of dogmatists who were suppressing science. Some of them were rather smart but they were still dogmatists. However, what would be wrong to imagine is that Galileo was tortured in a dungeon. <br /><br /><a href="https://artuk.org/discover/artworks/milton-visiting-galileo-when-a-prisoner-of-the-inquisition-125949" rel="nofollow"><img src="https://d3d00swyhr67nd.cloudfront.net/w1200h1200/CDN/CDN_WELL_L_51761.jpg" width=407></a><br /><br />Instead, this is how Solomon Alexander Hart (1806-1881) saw Milton's visit to Galileo when the latter was imprisoned. Galileo lived in a pretty fancy prison, right? He had what he needed to keep on thinking. You may compare Galileo's fancy spaces to the <a href="https://www.google.com/search?q=witten+office&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&biw=1317&bih=708" rel="nofollow">modest, prison-like office of Edward Witten's</a> or, if your stomach is strong, to <a href="https://www.google.com/search?q=guth+office&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&biw=1317&bih=708">Alan Guth's office</a>, voted the messiest office in the Solar System. ;-)<a name='more'></a><br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:block; text-align:center;" data-ad-layout="in-article" data-ad-format="fluid" data-ad-client="ca-pub-8768832575723394" data-ad-slot="4218709518"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />Hasn't the Catholic Inquisition provided Galileo with a kind of luxury that Guth can't dream about? (Sorry, Alan, I have abused the fact that no one has access to my rooms LOL.)<br /><br />OK, Galileo wasn't murdered by those intellectually inferior Catholic apparatchiks. Even his local comfort wasn't locally reduced. He was really "just" prevented from enjoying the freedom to interact with the mankind and to publish anything he wanted, from fully and directly influencing the intellectual world which a man of Galileo's caliber has deserved and which would have been beneficial for the mankind.<br /><br />These days, it's happening to conservative philosophers and also to thinkers who study ideas more deeply than the masses indoctrinated by embarrassing antiscientific superstitions such as the climate change panic, psychological equality of men and women, and similar nonsense which may be classified as overwhelmingly far leftist these days.<br /><br /><script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <ins class="adsbygoogle" style="display:inline-block;width:336px;height:280px" data-ad-client="ca-pub-8768832575723394" data-ad-slot="0363397257"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script><br /><br />I am convinced that the number of young people who want to do very high-brow things – like string theory research – has dropped sharply in a recent decade. I still try to follow who these people are. But as recently as two decades ago, the identity of these smartest people on Earth would be a matter of exciting debates. Who is the new young Susskind, Witten, or Schwinger? These days, I don't want to mention the names of the smartest theoretical physicists below 30 or stuff like that because I feel that the very publicity would hurt them.<br /><br />These ingenious people have to hide from the public eye because the mass culture of 2019 prefers mediocrity, mindless obedience, laziness, and superficial spitting on all the essential structures and mechanisms in Nature and the society (Greta Thunberg is quite a symbol for many pathologies of the present) and these people don't fit into that picture.<br /><br />Under the most recent post "Falsifiability and physics" (promoting the <a href="https://motls.blogspot.com/2019/04/popper-self-described-anti-dogmatist.html?m=1">dogmatist and fundamentally flawed Popperist memes</a>), an <a href="http://www.physics.rutgers.edu/~lath/">experimental (and therefore impartial) particle physicist</a> from Rutgers, my Graduate Alma Mater, has pointed out that the students planning to learn and do string theory are the cream:<br /><blockquote><b>Amitabh Lath</b>: the longevity of string theory is not due to the middle-aged practitioners you mention but kids in their early 20s who continue to choose to go into the field. Some of the best undergraduate students in our high energy experiment group have over the years chosen to go to grad school in theoretical physics 🙁 <br /><br />Some go into phenomenology but some are indeed doing string theory. <br /><br />These students are the smartest and most sensible I have ever met, the cream of the Garden State [New Jersey]. They devour the literature, they are fully aware of the arguments on all sides. I cannot in any seriousness entertain the idea that they are led astray by hyperbole. I believe all the arguments about string theory not having made any progress in decades, not producing any testable results, being stuck in a made-up universe nothing like our own reality; these are not deterrents but attractions to this type of student.<hr><br />I understand your point but the decisions made by these top tier students does much more to sway these “people who might have something to say about whether string theory research gets supported” than some national lab’s public outreach ‘zine.<br /><br />Every grad program wants these students: sky-high physics-GRE, letters dripping with superlatives, transcripts with half a dozen graduate level courses completed as undergrad. They are courted with fellowships and awards. Their eagerness to join the field is seen as proof of vibrancy. If a big-name string theorist leaves your department and the acceptance rate for these blue-chips drops, you know the search committee will form quickly.<br /></blockquote>It's natural that this is how it works. A young person who has the ability to master these cutting-edge questions in physics has a significant probability to <em>exploit the ability</em> and actually try to move the cutting edge a little bit further. This is an instinct. An instinct that starts with curiosity. When they have an intellectual weapon in their skull, they're rather likely to realize it and they don't want the weapon to be wasted. Finding important things in physics is, in many ways, more exciting than sex. But in many ways, these two instincts are analogous. The men who have a very potent weapon in between their limbs also want to exploit it in many cases.<br /><br /><iframe width="407" height="277" src="https://www.youtube.com/embed/d5TUFF0G79w" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe><br /><br /><em><a href="https://motls.blogspot.com/2019/04/alessandros-essay-in-quillette.html?m=1">The Czecho-Slovak Easter Monday Whip</a> is over. On April 30th, be ready for another nice tradition, the <a href="https://en.wikipedia.org/wiki/Walpurgis_Night#Czech_Republic" rel="nofollowing">burning of the witches</a>. Prepare every witch – basically every obnoxious woman or a female thief who has a visually understandable problem with beauty, even if she claims not to be a witch – pour some petrol to her glass to improve her mood, and burn her on Tuesday.</em><br /><br />Moving the cutting edge of physics a little bit (or a big step) forward isn't easy, all these people know. If one succeeds, he or she unavoidably establishes that the likes of Edward Witten, Andy Strominger, Leonard Susskind, and/or others have been doing something silly. Or they overlooked some known insights that were relevant at another place. To have a chance to establish these far-reaching insights and change the <em>status quo</em>, one has to be smart <em>and</em> hard-working, these young people know.<br /><br />It seems that the critics of science don't even get this simple point – that one needs intelligence and hard work to move theoretical physics forward.<br /><blockquote><b>A vanilla science critic:</b> ...but if you are writing about a controversy, aren’t you supposed to contact people on both sides?<br /></blockquote>What the author of these comments apparently fails to get is that science isn't a subset of journalism and scientists aren't assistants to journalists. You may call some people's irrational hostility towards a theory that they haven't mastered a "controversy". Be my guest. There is a "controversy" about string theory – there is a "controversy" about everything else, too. It's still much more accurate to call it a "difference between experts and ignorant yet self-confident simpletons". A journalist may cover the "controversy" but by doing so, he doesn't contribute to the science itself, either, and the audience expected to consume stories about these "controversies" can't be scientists, either, because the scientists know that the opinions of those who just haven't mastered the subject that they scream about are 100% worthless.<br /><br />In particular, the "journalistic" critique above was about the Symmetry Magazine. But the <a href="https://motls.blogspot.com/2019/04/physicists-views-have-been-confined-to.html?m=1">Symmetry Magazine isn't a generic journalists' outlet</a> describing "controversies" between the experts and the laymen. The Symmetry Magazine is an outlet whose purpose is to inform particle physicists and people who feel close to that field about the events in their field, not another outlet for the scientifically illiterate public that wants to read about "controversies" and unreasonably think that both sides are always equal. Angry ignorant laymen's rants <em>aren't</em> events in particle physics. The readers who read about such "controversies" are scientifically illiterate and scientifically inconsequential simpletons themselves. People who understand what the scientific method is <em>know</em> that the actual controversies in science are fought with scientific arguments, not just with the screaming of random angry men and their mobs in the popular books, mainstream press, or comment sections of random websites on the Internet.<br /><br />The simple fact that screaming by these critics is 100% irrelevant for science is sometimes proven to a comical extent. Peter Shor of MIT, the guy who invented an algorithm for quantum computers, wanted to discuss whether a recent AdS/CFT paper involving quantum error correction was right, consistent with another, whether a deformation brought the authors outside the error correction codes, and whether this fact invalidates the analysis (these are two different questions – a point Shor seems to misunderstand). The host intervened:<br /><blockquote><b>A vanilla critic of science</b>: All, I fear this is the wrong place to debate the issues raised by Peter Shor about CFT and error-correcting codes, partly because the moderator knows nothing about the topic (he would like to someday understand what that’s about, but today is not the day…)<br /></blockquote>You know, this emerging discussion was a part of something broader – they weren't sure whether the conclusions of the AdS/CFT ("quantum gravity in a box") were telling us something about our dS Universe, too. But as soon as any <em>actual scientific arguments</em> start to emerge, the host immediately stops the discussion because <em>science isn't allowed there at all</em>. The host even admits that the reason is that he actually knows <em>nothing</em> about the relevant science himself. Not only the host fails to encourage science (like I do here) – he actively bans it. Only superficial would-be philosophical prejudiced slogans are allowed. It's not even wrong. It's not even wrong. Orange man is bad. Orange man is bad. A worthless website run by mindless NPCs. In spite of that complete isolation from any insights about the AdS/CFT, the host still loves to make far-reaching claims about AdS/CFT. How dumb does a reader has to be to take any of these statements seriously?<br /><br />I think that every person whose IQ is above 80 understands that the relevance of such discussions for the cutting-edge theoretical physics is much closer to the relevance of opinions of the cattle utilized by the McDonald's Corporation than to the relevance of young or old string theorists' opinions. But we are surrounded by mobs that tend to threaten you even if and when you make this self-evident innocent point. A journalist may write for the readers with the IQ below 80 who think that the string theorist's and critic's opinions about string theory are equally valuable. But journalists aren't and mustn't be <em>obliged</em> to address all their texts to moronic readers!<br /><br />Before the discussion about any detailed issues in AdS/CFT, some participants mentioned the question whether string theorists are actually doing string theory these days:<br /><blockquote><b>A vanilla critic of science</b>: What I see happening now (at least in the US) is that the best students are, as always, going to a small number of the top graduate programs (e.g. Harvard, Princeton, Stanford), where most of the theory faculty often identify tribally as “string theorists”, but are now working on topics in GR/QFT/quantum information, etc. that have nothing to do with quantized strings or with string-theory based unification. The odd thing I keep hearing is that such students arriving at such a grad program are encouraged to spend a lot of time studying actual string theory (e.g. by reading Polchinski’s two volumes) to prepare to start research, even though the research likely won’t use any of this. <br /></blockquote>What's going on here? The smartest undergraduate students are still capable of figuring out which places actually have the best theoretical high-energy physics in the world – and be sure that Harvard, Princeton, Stanford are <em>at least</em> near the top of the list. So they go there and the top physicists over there push them to study string theory.<br /><br />Is that right?<br /><br />Of course it's right. If you are a graduate student who says that your specialization is formal enough, non-phenomenological theoretical high-energy physics, you simply <em>have to</em> master string theory which is the state-of-the-art picture of theoretical high-energy physics as of 2019. In fact, string theory was born 51 years ago. It would be ludicrous to say that it's some recent fad or something that theoretical high-energy physicists may ignore in 2019. And if graduate students at Princeton, Harvard, Stanford were ignoring it, it would be really really bizarre.<br /><br />In principle, you may make some important contribution to theoretical physics <em>without</em> knowing the state-of-the-art apparatus. You deserve a PhD if you do so. But you don't deserve a PhD just for a <em>chance</em> that it happens. If you haven't made a real breakthrough, you only deserve a theoretical physics PhD if you have mastered the tools close enough to the cutting edge of a sub-discipline that give you a reasonable chance to make a breakthrough later. In particular, <em>you should learn the damn string theory</em>.<br /><br />I think that the percentage of non-stringy papers written by string theorists is much higher than two decades ago or even one decade ago. I also believe that the political atmosphere in the broader society is one of the main culprits – probably the main culprit. So people do various things – string theorists may do <em>many things</em>, indeed. I am also convinced that most of the stringy authors of such non-stringy articles realize that their non-stringy research is less profound than the string research they could do a decade or two ago. But it's OK enough for them.<br /><br />The situation is completely analogous to the times of Johannes Kepler and Tycho Brahe. They were employed by our glorious and playful leader, Rudolph II who reigned from Prague (I just watched the hilarious Czech movies The Baker's Emperor and The Emperor's Baker), and they were getting much of their income for <em>astrology</em>. Is it right to criticize these famous astronomers for getting some money from astrology? I don't think so. It wasn't primarily their fault. They preferred to do things that would soon lead to Newton's physics. But the <em>society and the powerful</em> wanted them to do things like the horoscopes. And these activities were easy enough for the astronomers because the skills are similar to the <em>serious astronomy</em> which helped to make sure that they actually did some astrology. Well, these old physicists and astronomers actually liked astrology to some extent, too. But this positive attitude wasn't a <em>characteristic</em> trait of them. They were also products of their epoch.<br /><br />Obviously, what the string theorists do outside string theory is much more scientific than the horoscopes but the basic dynamics is the same. What the researchers do <em>is affected</em> by the societal pressures and pressures from the sponsors etc. And because lots of the ignorant activists have pushed the image of string theory to something similar to the heliocentric heresies 4 centuries ago, string theory is also being hidden from the public eye to a similar extent as heliocentrism was 4 centuries ago. It became at least questionable whether you may materially benefit from stringy results that you produce – even if they are rather important ones. It doesn't mean that there's something non-essential or even wrong about heliocentrism or string theory. It is just a reflection of irrational beliefs that are prevalent among the laymen in one epoch or another.<br /><br />The top theoretical physicists still have the duty – and internal instincts – to preserve the field. So even when the pressures make it likely for the new PhDs to work on something else or to produce horoscopes, it's still essential that the knowledge of string theory doesn't evaporate when a new generation replaces the previous one. A top university simply cannot give a theoretical physics PhD to someone who just solves the average exercises in a textbook of quantum field theory – or who writes diatribes against theoretical physics. If this became normal at such a university, that university would clearly cease to be a top one because <em>almost everybody can do such things</em>. People who succeed as writers of anti-scientific diatribes aren't exceptional because they are <em>exceptionally good</em>. They succeed because they are <em>exceptionally close to the average people</em>.<br /><br />If the last 20 papers by a string theorist were about "non-string theory", does it make sense for him or her to be called "a string theorist"? You bet. If he or she hasn't forgotten the theory, it's still the most accurate description of his or her expertise. A string theorist is someone who has mastered and/or done some research on string theory – which also required him or her to become a good enough expert in quantum field theory (and all of its prerequisites; and it's likely that an average "string theorist" understands QFT more than an average "quantum field theorist"), some algebraic geometry, general relativity, quantum information, and more. These folks first needed to master the prerequisites and <em>then</em> they could jump on string theory which added some expertise that is equivalent to a few more years of studying.<br /><br />The reason why such people – regardless of the detailed content of the recent papers – call themselves "string theorists" and not e.g. "quantum field theorists" is exactly the same as the reason why a person both with a bachelor and doctor degree prefers to call herself a "doctor": it's simply the superior degree! Being a string theorist <em>does incorporate</em> being a quantum field theorist and other things. So why would a string theorist call himself a quantum field theorist? Why would a doctor call himself a bachelor? Why would Kepler call himself an astrologer (as the primary job description) if he were also and primarily an astronomer?<br /><br />During Kepler's times, certain people wanted to turn astronomy, especially the heliocentric astronomy, into a heresy. Some of them might have preferred the masses to imagine that being an astrologer was more important. But the actual <em>experts</em> knew it wasn't the case. They <em>already knew</em> that astronomy was more important than astrology. It was more scientific. It also required more time and hard work to be studied and researched. The smartest folks actually knew that the astronomers (and consumers of astronomy) were smarter in average than astrologers (and consumers of horoscopes in particular). This knowledge has always affected what they emphasized while talking to each other.<br /><br />Completely analogously, some people want to mislead masses and hide the simple basic fact that e.g. the <em>string theory graduate students are generally smarter and more advanced</em> than the average graduate students who have learned quantum field theory at a decent level. And this misinformation of the masses may work. But by definition, it doesn't affect the genuine experts who have actually studied these things and who interact with string theorists as well as the people in adjacent fields. Those still <em>know the truth</em>.<br /><br />Most of the critics of string theory <em>know</em> that they're simply lying 24 hours a day, 7 days a week. And I have doubts that they get some real psychological relief from the deception. Why? Because they still know that the people who buy this ridiculous garbage – such as the claim that it's just OK for an intelligent theoretical physicist to dismiss string theory – are just easily manipulated dimwits. They still know that these dimwits' opinions don't matter for the science itself. One can manipulate hundreds of easy-to-manipulate dimwits but it still doesn't change the underlying truths. Is it more psychologically pleasing when some uncritical readers repeat some slogans? Does it make the "trainer" more psychologically satisfied than when he trains a parrot – an actual bird – to repeat a sentence? The parrots' achievements look more remarkable to me because the birds are punching above their weight. The average human's repetition of average stupid slogans is the business-as-usual.<br /><br />I find it staggering how completely these critics of science misunderstand what science is and how it works:<br /><blockquote><b>A vanilla critic of science:</b> What’s disturbing to me is that, increasingly, the string unification/SUSY research program seems to have moved from “evaluate us by LHC results or progress on these crucial problems that are in between us and a testable theory” to “there is no way to evaluate us, you just have to believe us, because there are so many of us and we’re so smart.” That’s not the way science is supposed to work, for good reason.<br /></blockquote>The number of string theorists isn't large (as in "many of us"). The currently professional ones are around 1,000 – it's a big part of the intellectual cream of the mankind. But the claim that "the layman has no way to evaluate them" is self-evidently true and it was always true. A non-expert who hasn't mastered even the basic chapters of a textbook about a given field obviously cannot evaluate – and could have never evaluated – the statements about the field. Why would someone doubt this self-evident fact? Only if one actually works and becomes an expert herself, to one extent or another, she can start to (meaningfully) evaluate the statements about the field.<br /><br />In theoretical high-energy physics, the results from the LHC influence the physicists' beliefs about many questions (but surely not all questions that these physicists investigate), but you still need expertise to figure out what the LHC collisions actually imply for the validity of various big statements about particle physics. The layman just doesn't know and can't know how to deduce some truths about deep questions from the LHC collisions. For example, a layman just cannot have a reasonably justified opinion on whether the Standard Model or the MSSM is more likely at this point, after some 160/fb of data collected by major LHC detectors (and after many theoretical advances). Everyone who has been persuaded that this is possible without real expertise in theoretical physics has been deceived.<br /><br />The non-expert may choose to believe or not believe, it's his psychological dilemma, but whatever he chooses doesn't <em>affect</em> the scientific truth in the field – in this case string theory. A rational expert who doesn't really understand anything about the theory at the technical level should primarily realize that <em>he doesn't know</em> what the truth is. To some extent, even the experts <em>do not know</em> the answers to many questions, even the very important ones. The ability to live in the state of ignorance is one of the first conditions for the scientific attitude to the world. A person who just "needs" to pick some answers, even if they have at least 50% probability to be wrong, just isn't approaching the truth in the scientists' way.<br /><br />The very act of choosing to "believe" – or "not believe" – is an irrational move. And "not believing" is obviously as irrational as believing! Well, it's a bit more irrational because even a layman should be able to figure out (a sociological argument) that the critics are less informed and less intelligent and therefore less likely to be true than the experts chosen by the intelligence.<br /><br />And the actual dynamics of the funding and support of pure science in a healthy society <em>should work</em> exactly in the way that the vanilla critic of science tries to mock: the society <em>should</em> give some support and funding to the <em>smartest yet curious people to do the research wherever it seems to lead</em>, whatever the generic members of the society think about the direction in advance. This really <em>is</em> the cornerstone of science or any honest research (or police investigation). You just follow the evidence wherever it leads. And it's only the smart yet hard-working people who meaningfully manipulate with the evidence who have a high enough chance to move theoretical physics forward.<br /><br />The researchers must have the freedom to do their pure scientific research as they see fit. And the people who are allowed to (and have the material backing) do this kind of a job should be chosen meritocratically – as the most intelligent and those who have mastered the "previous" picture of physics better than others – and not according to the proximity of their opinions and beliefs to the opinions of masses! The other, critic's approach would liquidate the science and it would turn the ex-scientists into corrupt defenders of sponsors' or the public's prejudices.<br /><br />So yes, please. When these dark ages are over and almost all people realize once again why the ideology and methods of the critics have been medieval and pathological, the nations will support at least a few thousand of the smartest yet curious people to do the pure scientific research according to <em>their own judgement and their own evaluation of the evidence as they see it</em> – not according to the judgement and prejudices of the society – because this picture where "only the scientific evidence matters" is how science differs from the irrational and oppressive enforcement of orthodoxies for the masses!<br /><br />And that's the memo.Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.com0