## Friday, September 16, 2016 ... /////

### String theory lives its first, exciting life

Gross, Dijkgraaf mostly join the sources of deluded anti-string vitriol

Just like the Czech ex-president has said that the Left has definitively won the war against the Right for any foreseeable future, I think it's true that the haters of modern theoretical physics have definitively won the war for the newspapers and the bulk of the information sources.

The Quanta Magazine is funded by the Simons Foundation. Among the owners of the media addressing non-experts, Jim Simons is as close to the high-energy theoretical physics research community as you can get. But the journalists are independent etc. and the atmosphere among the physics writers is bad so no one could prevent the creation of an unfortunate text

The Strange Second Life of String Theory
by Ms K.C. Cole. The text is a mixed, and I would say mostly negative, package of various sentiments concerning the state of string theory. Using various words, the report about an alleged "failure of string theory" is repeated about 30 times in that article. It has become nearly mandatory for journalists to write this spectacular lie to basically every new popular text about string theory. Only journalists who have some morality avoid this lie – and there aren't too many.

With an omnipresent negative accent, the article describes the richness or complexity of string theory as people have understood it in recent years and its penetration to various adjacent scientific disciplines. What I find really annoying is that some very powerful string theorists – David Gross and Robbert Dijkgraaf – have basically joined this enterprise.

They are still exceptions – I am pretty sure that Edward Witten, Cumrun Vafa, and many others couldn't be abused to write similar anti-string rants – but voices such as Gross' and Dijkgraaf's are the privileged exceptions among the corrupt class of journalist hyenas because they are willing to say something that fits the journalists' pre-determined "narrative".

OK, let me mention a few dozens of problems I have with that article.
The Strange Second Life of String Theory
It's the title. Well, it's nonsense. One could talk about a second life if either string theory had died at some moment in the past and was resuscitated; or if one could separate its aspects to two isolated categories, "lives".

It's spectacularly obvious that none of these conditions holds. String theory has never "died" so it couldn't have been resuscitated for a second life. And the applications here and there are continuously connected with all other, including the most formal, aspects of string theory.

So there's simply just one life and the claim about a "second life" is a big lie by itself. The subtitle is written down to emphasize the half-terrible, half-successful caricature of string theory that this particular writer, K.C. Cole, decided to advocate:
String theory has so far failed to live up to its promise as a way to unite gravity and quantum mechanics. At the same time, it has blossomed into one of the most useful sets of tools in science.
Well, string theory has been known to consistently unify gravity and quantum mechanics from the 1970s, and within fully realistic supersymmetric models, since the 1980s. Already in the 1970s, it was understood why string theory avoids the ultraviolet divergences that spoil the more straightforward attempts to quantize Einstein's gravity. In the 1980s, it was shown that (super)string theory has solutions that achieve this consistency; but they also contain forces, fields, particles, and processes of all qualitative types that are needed to explain all the observations that have ever been made. Whether or not we know a compactification that precisely matches Nature around us, we already know that string theory has proven that gravity and quantum mechanics are reconcilable.

So already decades ago, string theory has successfully unified gravity and quantum mechanics. No evidence whatsoever has ever emerged that something was wrong about these proofs of the consistency. So the claim about the "failure" to unify gravity and quantum mechanics is just a lie.

You may see that Cole's basic message is simple. She wants to claim that string theory is split to two parts, a failed one and a healthy one. Moreover, the failed one is all the core of string theory – all the conceptual and unification themes. The reality is that the split doesn't exist; and the formal, conceptual, unification theme in string theory is the essential and priceless one.

This deceitful theme is repeated many, many times by K.C. Cole in her text. There are lots of other deceptions, too:
To be sure, the theory came with unsettling implications. The strings were too small to be probed by experiment and lived in as many as 11 dimensions of space.
Both of these "unsettling implications of string theory" are just rubbish. It's very likely that strings are very small and the size is close to the fundamental Planck scale, $10^{-35}$ meters. But this wasn't a new insight, as you might guess if you were capable of noticing the name "Planck" in the previous sentence. Max Planck determined that the fundamental processes of Nature probably take place at the distance of the Planck length more than 100 years ago.

It follows directly from dimensional analysis. There may be loopholes or not. The loopholes were imaginable without string theory and they are even more clearly imaginable and specific with string theory (old and large extra dimensions etc.). But string theory has only made the older ideas about the scale more specific. The ultrashort magnitude of the Planck length was in no way a new implication of string theory.

The existence of extra dimensions of space may be said to be string theory's implication. Older theories were trying to unify electricity and magnetism already in 1919 but string theory has indeed made those extra dimensions unavoidable. But what's wrong is that this implication is "unsettling". The existence of extra dimensions of some size – which may be as short as a "few Planck lengths" but may also be much longer – is a wonderful prediction of string theory that is celebrated as a great discovery.

Although it is not "experimentally proven as a must" at this point, it is compatible with all observations we know and people who understand the logic know very well that the extra dimensions wonderfully agree with the need for a structure that explains the – seemingly complicated – list of particles and interactions that has been discovered experimentally. This list and its complexity are in one-to-one correspondence with the shape and structure of the extra dimensions. This identification – the particle and fields spectrum is explained by the shape – sounds wonderful at the qualitative level. But calculations show that it actually works.

So when someone assigns negative sentiments to this groundbreaking advance, she is only exposing her idiocy.

It's more frustrating to see what David Gross is saying these days:
For a time, many physicists believed that string theory would yield a unique way to combine quantum mechanics and gravity. “There was a hope. A moment,” said David Gross, an original player in the so-called Princeton String Quartet, a Nobel Prize winner and permanent member of the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara. “We even thought for a while in the mid-’80s that it was a unique theory.”
What people believed for a few months in the mid 1980s was that there was a unique realistic compactified string theory to $d=4$. It was understood early on that there existed compactified string theories that don't match the particle spectrum we have observed. But it was understood that there could be one that matches it perfectly. And it's still as true as it was 30 years ago. The theoretically acceptable list of solutions is not unique but the solution that describes Nature is unique.

Moreover, in the duality revolution of mid 1990s, people realized that all the seemingly inequivalent "string theories", as they would call them in the previous decades, are actually connected by dualities or adjustments of the moduli. So they're actually not separate theories but mutually connected solutions of one theory. That's why all competent experts stopped using the term "string theories" in the plural after the duality revolution.

David Gross likes to say that "string theory is a framework" – in the sense that it has many "specific models", just like quantum field theories may come in the form of "many inequivalent models", and these models share some mathematical methods and principles while we also need to find out which of them is relevant if we want to make a particular prediction.

So far so good. But there's also a difference between quantum field theory and string theory. Two different QFTs are really distinct, inequivalent, different theories – encoded in a different Lagrangian, for example, and there's no way to get the objects from one theory with one Lagrangian in the QFT of another theory with a different Lagrangian. But in string theory, one can always get objects of one kind by doing some (possibly extreme, but finite) change of the space or vacuum that starts in another solution. All the different vacua and physical objects and phenomena in them do follow from some exactly identical, complete laws – it's just the effective laws for an expansion around a (vacuum or another) state that may come in many forms.

String theory is one theory. No legitimate "counter-evidence" that would revert this insight of the 1990s has been found ever since. Gross adds some "slightly less annoying" comments as well. However, he also escalates the negative ones. "There was a hope," Gross said, later suggesting that there's no "hope" anymore. But there's one even bigger shocker from Gross:
After a certain point in the early ’90s, people gave up on trying to connect to the real world.
WTF!? Did Gross say that string phenomenology hasn't existed "from the early 1990s"?

Maybe you completely stopped doing and even following string phenomenology but that's just too bad. The progress has been substantial. Just one subdirection that was basically born in the last decade. Vafa's and pals' "F-theory with localized physics on singularities" models of particle physics. Let me pick e.g. Vafa-Heckman-Beasley 2008 as the starting point. 350 and 400 followups, respectively. Recent advances derive quite some interesting flavor and similar things – e.g. neutrino oscillations including the recently observed nonzero $\theta_{13}$ angle – out of F-theory.

And this is just a fraction of string phenomenology. One could spend hours by descriptions how heterotic or M-theory phenomenology advanced e.g. from 2000. Did you really say that "people gave up on trying to connect to the real world" over 20 years ago, David? It sounds absolutely incredible to me. Maybe, while you were criticizing Joe and others for their inclinations to the anthropic principle and "giving up", you accepted this defeatist stuff yourself, and maybe even more so than Joe did, at least when it comes to your thinking or not thinking about everything else.

Maybe you – and Dijkgraaf – now think that you may completely ignore physicists like Vafa because you're directors and he isn't. But he's successfully worked on many things including the connections of string theory to the experimental data which is arguably much more important than your administrative jobs. This quote of Gross' sheds new light e.g. on his exchanges with Gordon Kane. Indeed, Gross looks like a guy who stopped thinking about some matters – string phenomenology, in this case – more than 20 years ago but who still wants to keep the illusion that he's at least as good as the most important contemporary researchers in the discipline. Sorry but if that's approximately true, then Gross is behaving basically like Peter W*it. There may be wrong statements and guesses in many string phenomenology papers but they're doing very real work and the progress in the understanding of the predictions of those string compactifications has been highly non-trivial.

Vafa and Kane were just two names I mentioned. The whole M-theory on $G_2$ manifolds phenomenology was only started around 2000 – by Witten and others. Is this whole research sub-industry also non-existent according to Gross? What about the braneworlds? Old large and warped dimensions? Detailed stringy models of inflation and cosmology in general? Most of the research on all these topics and others took after the mid 1990s. Are you serious that people stopped thinking about the connections between strings and experiments?

But Robbert Dijkgraaf contributes to this production of toxic nonsense, too:
“We’ve been trying to aim for the successes of the past where we had a very simple equation that captured everything,” said Robbert Dijkgraaf, the director of the Institute for Advanced Study in Princeton, New Jersey. “But now we have this big mess.”
Speak for yourself, Robbert. The fundamental laws of a theory of everything – of string theory – may be given by a "very simple equation". And I've been attracted to this possibility, too, especially as a small kid. But as an adult, I've never believed it was realistic – and I am confident that the same holds for most of the currently active string theorists. In practice, the equations we had to use to study QFT or string theory were "never too simple". Well, when I liked string field theory and didn't appreciate its perturbative limited character, I liked the equations of motion of the background-independent version of string field theory,$A * A = 0.$ That was a very attractive equation. The string field $A$ acquires a vacuum condensate $A_0$, i.e. $A=A_0+a$, composed of some "nearly infinitesimal strings" such that $A_0 * \Phi$ or an (anti)commutator is related to $Q \Phi$ acting on a string and encodes the BRST operator $Q$. The terms $Qa$ impose the BRST-closedness of the string states. The equation above also contains the residual term $a*a$ which is responsible for interactions. The part $A_0*A_0=0$ of the equation is equivalent to the condition for the nilpotency of the BRST operator, $Q^2=0$.

It's fun and (at least open, perturbative) string theory may be derived from this starting point. At the same moment, this starting point doesn't seem to allow us to calculate effects in string theory beyond perturbative expansions – at least, it doesn't seem more potent in this way than other perturbative approaches to string theory.

OK, I want to say that a vast majority of what string theorists have been doing since the very beginning of quantitative string theory, in 1968, had nothing to do with $A*A=0$ or similar "very simple equations". Maybe Robbert Dijkgraaf was obsessed with this idea of "very simple equations" when he began to study things like that but I never was and I think that most string theorists haven't. Already when I was a kid, it was rather clear to me that one needs to deal with some "rather difficult equations" if he wants to address the most fundamental laws of physics. "Próstoj prostóty něbudět," ("There won't be any simple simplicity any longer") was a favorite quote I picked from Lev Okun's popular book on particle physics when I was 16 or so and since that moment, I was almost never believing something different.

There's still some kind of amazing "conceptual simplicity" in string theory but it's not a simplicity of the type that a very short equation could completely define everything about physics that we need and would be comprehensible to the people with some basic math training. A very simple equation like that could finally be found but the advances in string theory have never led to any significant evidence that a "very simple equation" like that should be behind everything. At least so far.

Nothing has changed about these basic qualitative matters since 1968. So Dijkgraaf's claim that string theorists have been doing research by looking for some "very simple equation" and only recently, they found reasons that this is silly, is simply a lie. This "very simple research" was never any substantial part of the string theory research and nothing has changed about these general matters in recent years or decades.

And what about the words "big mess"? What do you exactly count as parts of the "big mess"? Are the rules about the Calabi-Yau compactifications of heterotic string theory a part of the "big mess"? What about matrix string theory? AdS/CFT and its portions? Sorry, I would never use the term "big mess" for these concepts and dozens or hundreds of others. They're just parts of the paramount knowledge that was uncovered in recent decades.

Maybe, Robbert, you fell so much in love with your well-paid job of the director that you now consider the people in the IAS and elsewhere doing serious research to be inferior dirty animals that should be spitted upon. If that's the case, they should work hard to remove you. Or do it like the tribe in Papua-New Guinea.

To make things worse:
Its tentacles have reached so deeply into so many areas in theoretical physics, it’s become almost unrecognizable, even to string theorists. “Things have gotten almost postmodern,” said Dijkgraaf, who is a painter as well as mathematical physicist.
"Tentacles" don't exactly sound beautiful or friendly – well, they're still friendlier than when someone calls all these insights "tumors". But the claim that string theory has become "unrecognizable to string theorists" is just rubbish, too. Applications of string theory in some other disciplines – e.g. in condensed matter physics – may be hard for a pure string theorist. But that's because these applications are not just string theory. They are either "modified string theory" or "string theory mixed with other topics" etc.

Nothing has become "less recognizable" let alone "postmodern" about pure string theory itself. It's a theory including all physics that may be continuously connected to the general perturbative formula for S-matrix amplitudes that uses a conformal-invariant, modular-invariant theory on a two-dimensional world sheet. Period. The actual "idea" about the set of all these possible phenomena remains clear enough. There are six maximally decompactified vacua of string theory and a large number of compactified solutions that increases with the number of compactified dimensions.

The number of all such solutions and even of the elements of some subsets may be very large but there is nothing "postmodern" about large numbers. Mathematics works for small numbers as well as large numbers. Postmodernism never works. These – richness of a space of solution and postmodernism – are completely different concepts.

Now, boundaries between string and non-string theory.
“It’s hard to say really where you should draw the boundary around and say: This is string theory; this is not string theory,” said Douglas Stanford, a physicist at the IAS. “Nobody knows whether to say they’re a string theorist anymore,” said Chris Beem, a mathematical physicist at the University of Oxford. “It’s become very confusing.”
One interpretation of Beem's words is a worrisome one: He is a rat who wants to maximally lick the rectums of the powerful ones and because dishonest and generally f*cked-up string theory bashers became omnipresent and powerful, he is tempted to lick their rectums as well. So he may want to say he isn't a string theorist.

But even with the more innocent interpretation of the paragraph above, it's mostly nonsense. Just look at the list of Chris Beem's particular papers. It's very clear that he is mostly a quantum field theorist. Even though he co-authored papers with many string theorists – I know many of his co-authors – it isn't even clear from the papers whether all the authors had to be given the basic education in the subject.

It's not clear whether Chris Beem is a string theorist but it's not because string theory is ill-defined. It's because it's not clear what Chris Beem is actually interested in, what he knows, and what he works on.

There is work on the boundary of "being pure string theory" and "having no string theory at all". But there's nothing "pathological" about it. The situation is completely analogous to the questions in the 1930s whether some papers and physicists' work were on quantum mechanics as understood in the 1920s, or quantum field theory. Well, quantum field theory is just a more complete, specific, sophisticated layer of knowledge built on top of quantum mechanics – just like string theory is a more complete, specific, sophisticated layer of knowledge built on top of quantum field theory.

In the late 1920s and the 1930s, people would start to study many issues such as the corrections to magnetic moments, hydrogen energy levels from the Lamb shift (virtual photons) etc. They could have "complained" in exactly the same way: We don't know whether we're working on quantum mechanics or quantum field theory. Well, both. It's clear that you can get far enough if you think of your research as some "cleverly directed" research on some heuristic generalization of the old quantum mechanics. But you may also view it as a more rigorous derivation from the newer, more complete theory. Once the more complete, newer theory is sufficiently understood, people who understand it know exactly what they're doing. Some people don't know it as well.

Exactly the analogous statements may be made about the research on topics where the "usual QFT methods aren't enough" yet the goals look more QFT-like and less string-like than the goals of the most "purely stringy" papers. So why the hell are you trying to paint all trivial things negatively? There are many papers that have to employ many insights and many methods from various "subfields". And they often need to know many of these things just superficially. What's wrong about it? It's unsurprising that such papers can't be unambiguously categorized. Examples like that exist in (and in between) most disciplines of science.

What's actually wrong is that the number of people who do full-fledged string research has been reduced. I think that it has been reduced partly if not mostly due to the sentiment I previously attributed to Chris Beem – many people want to lick the aßes of the string-bashing scum that has penetrated many environments surrounding the research institutions. And the string-theory-bashing scum has tangibly reduced the funding etc.

David Simmons-Duffin, Eva Silverstein, and Juan Maldacena didn't say anything that could be interpreted as string-bashing in isolation. They explain that much of string theory is about interpolations of known theories or results; string theory has impact on cosmology and other fields; we don't know the role of the landscape in Nature around us (Maldacena also defines string theory as "solid theoretical research on natural geometric structures"). Nevertheless, K.C. Cole made their statements look like a part of the same string-bashing story.

There are lots of quotes and assertions in the article that are borderline and much less often completely correct but their "emotional presentation" is always bizarre in some way. But there are many additional statements that aren't right:
Toy models are standard tools in most kinds of research. But there’s always the fear that what one learns from a simplified scenario does not apply to the real world. “It’s a bit of a deal with the devil,” Beem said. “String theory is a much less rigorously constructed set of ideas than quantum field theory, so you have to be willing to relax your standards a bit,” he said. “But you’re rewarded for that. It gives you a nice, bigger context in which to work.”
Why does Mr Beem think that "string theory is a much less rigorously constructed set of ideas than QFT"? It's an atlas composed of "patches" that are as rigorously constructed as QFTs – because the patches are QFTs. So perturbative string theory is all about a proper analysis of two-dimensional conformal field theory. Everything about perturbative string theory is encoded in this subset of QFTs. Similarly, Matrix theory allow us to fully define physics of string/M-theory using some "world volume" QFTs and AdS/CFT allows us to define the gravitational physics in an AdS bulk using a boundary CFT which is, once again, exactly as rigorous as a QFT because it is a QFT. (Later in Cole's text, Dijkgraaf mentions that the right "picture" for a string theory could be an atlas, too.)

So what the hell is Beem talking about? And additional aßholes are being added to the article:
“Answering deep questions about quantum gravity has not really happened,” [Sean Carroll] said.
What? Does he say such a thing after the black hole thermodynamics was microscopically understood, not to mention lots of insights about topology change, mirror symmetry, tachyons on orbifold fixed points etc., and even after the people found the equivalence between quantum entanglement and non-traversable wormholes and many other things? Nothing of this kind has happened?

At the end, Nima Arkani-Hamed says:
If you’re excited about responsibly attacking the very biggest existential physics questions ever, then you should be excited. But if you want a ticket to Stockholm for sure in the next 15 years, then probably not.
I would agree with both sentences including the last one because it contains the word "probably". This prize is far more experimentally oriented and of course, many pieces of work (with lasers and other things) that are vastly less important than those in stringy and string-like theoretical physics have already been awarded by the Nobel prize. The Nobel prizes still look credible enough to me but I haven't been the child who's been parroting clichés that "it's great to get one" for over 25 years. It's simply not a goal of a mature physicist. On the other hand, I am not really certain that no one will get a Nobel prize for string theory in the following decade or two.

But I think it's no coincidence that just like the title, the last sentence of Cole's article is negative about string theory. Negativity about string theory is really "her main story". Too bad that numerous well-known people join this propaganda as if they were either deluded cranks or opportunity-seeking rats.