Wednesday, August 14, 2013

Some physics links

Carroll's QM, NYT's firewalls, Jester's whining on scales

Sean Carroll has unlocked the quantum chapter from his "Eternity" book,
Quantum Mechanics Made Easy,
which I found better than expected despite its misleading comments about the "collapse", "its" relationships with the "arrow of time", the meaning of the "Copenhagen Interpretation", the "many worlds" as the "leading alternative contender", and many other things (he omits Bohm etc.). Carroll's text is flawed in different ways than e.g. Brian Greene's musings about the interpretation of quantum mechanics but I wouldn't say it's "more flawed". I am still not aware of any popular presentation of the foundations of quantum mechanics that is done right.

Now, Dennis Overbye wrote quite an informative and long The New York Times article about the black hole firewalls and the ER-EPR correspondence,
A Black Hole Mystery Wrapped in a Firewall Paradox.
Overbye confirms his status as one of the world's best popular science writers who focuses on theoretical physics. As a reader, you are reminded about some of the intellectual stories of Einstein and Hawking as well as the interactions that made various people confuse each other about the firewall fallacy on the West Coast. Susskind whose opinions resembled a yo-yo hasn't changed his views for several months, we're told.

Incidentally, Bousso has a new paper about the firewalls and if I judged the situation according to everything that is written in these still equally confusing if not crazy papers (Bousso claims that there's a firewall even when the black hole is very young – a brutal violation of locality), I would have to agree that they're as confused as 40 years ago – something written in Overbye's article. In the real world, the claim that things haven't become much clearer in the last 40 years is an outrageously crazy lie. At least my understanding of all these questions is much better than even 15 years ago – perhaps because I don't change my mind whenever someone writes some new bullshit.

Most frequent surnames. Click for all 40 informative and funny maps that you will ever need. Via the Pirate of Prague.

There will be a workshop in Santa Barbara about these matters. It's organized by Don Marolf. He also posted his own new paper arguing that holography doesn't depend on strings. As far as I can see, it's a sloppy tirade full of unsubstantiated claims – well, the claims are supported at most by a vague analysis of something that has been analyzed very accurately since late 1997. We know pretty much exactly what the bulk stringy objects – strings and branes and black holes etc. – mean in the boundary CFT, when they matter, when they can be neglected, which properties of string theory are important and unimportant for various derivations (e.g. of black hole entropy), and so on. It's hard to imagine how a superficial paper such as Marolf's could be considered as anything else than a redundant, outdated, not quite competent, low-quality addition to the literature.

Finally, Jester at Resonaances published a new blog entry after 4 months or so (delay caused by "work, travel, frustration, depression, and sloth").

I agree with all of his "matter of fact" claims but I don't share his emotional reaction at all.

Jester says that since the 1930s, physicists – we would say phenomenologists – would be looking towards a holy grail, a high-energy scale, which always happened to be the electroweak scale. New physics had to be added to make the theory work. Now, the theory at the electroweak scale (the Standard Model) seems to be completed and consistent as a renormalizable quantum field theory so there's nothing else to "inevitably expect" at that scale – and the LHC confirms that except for the Higgs, this scale isn't "overflowing" with tons of new physics. So even though it's still likely but not certain that there's new physics such as SUSY at a nearby scale, the physicists have to look at another scale to achieve a certainty about new physics but he doesn't know which one.

So this is how the situation looks to Jester – and Savas. No clear direction for progress, they think.

Jester's claims about the physics are true but his reasons for frustration are inappropriate. What he dislikes is that regardless of the energy of the next (realistic) collider, \(30\TeV\), \(100\TeV\), or \(1,000\TeV\), we can't be quite sure that the collider finds new physics. I agree with that but I am not shocked by it in any way.

It has been clear to me that the Standard Model was a complete renormalizable theory – a theory that can be extrapolated to really, really high energy scales – since I was a college sophomore. (In the following year, I began to attend QFT courses: buy the book on the electroweak theory by my major undergraduate QFT instructor.) So of course that once all the necessary pieces of this Standard Model are established, there is no other new physics testable at the accelerators that is "inevitable" in an energy range that is "guaranteed".

One could say that I was solving similar questions as Jester but it was 20 years ago. Is that the first time when Jester realizes that the Standard Model is a complete renormalizable QFT that doesn't need extra additions? We know about some likely additions linked to the Higgs stability, hierarchy problem, dark matter, inflation etc. (Jester discusses them as well) but we're not guaranteed that they're accessible by any particular realistic collider.

Well, I have always even shared Jester's strategy to find an energy scale below which new physics is guaranteed. And I found it (so did Max Planck 100 years earlier although he didn't quite understand the physics of the scale). It's the Planck scale. New phenomena have to occur at the scale \(10^{19}\GeV\) or lower (it may be much lower in models with large or warped extra dimensions but the true fundamental scale can't be higher).

It would be fun if the scale could be accessed by direct experiments except that it seems unlikely and we have always thought it was unlikely. So why should we be "negatively surprised" now? I, for one, don't care much (and have never cared much) that Nature has made the scale so high that it's not accessible by our particle physics experiments. (Of course, the gap between the scales has to be this high because it's ultimately needed for the existence of life. Evolution of life requires lots of sunny days. Stars are long-lived because they contain many nuclei that may be burned and the number of nuclei ends up large because gravity is so much weaker than other forces and pressures so lots of nuclei are needed for the gravity to become significant and compensate the repulsive pressures.)

The Planck scale is the scale where my thinking about fundamental physics – and the thinking of any top-down theorist – begins. From this inaccessible scale, one may dig deeper perhaps down to the experimenters' scales but it has always been clear that the true fundamental scale where important things have to exist is the Planck scale. (Stringy and grand unified theories make it likely but not guaranteed that there are some interesting additional phenomena at scales slightly, perhaps 10-100 times, lower than the Planck scale, too.) Everything else are just optional islands alternating with optional deserts. You may demand that there is some land in the ocean at each 100 miles (and even claim that gaps in the ocean that are longer than 100 miles prove that geography is no science because you can't swim there) except that the rules of geography don't have to respect your demands. The existence and inner workings of Eurasia is mostly independent of America so – even though Jester may find it surprising – no one is guaranteed that there has to be an America at most 100 miles from Spain.

So what the confused headless hens show is just a minor thing – that the dogmatic bottom-up, direct-experiments-based view on fundamental physics isn't a sustainable strategy to keep the research going. All the people claiming that physicists are only allowed to think about things that must have consequences for particular near-future experiments have always been as deeply misguided as the Spanish Catholics who wanted to prevent Columbus from trying to sail to another continent around the round globe.

One has to think about topics that are behind the currently observable horizons if he wants to make real progress! We could say that the bottom-up paradigm is complete and dead and it's time for every single phenomenologist to learn some string/M-theory because this is the new physics that is guaranteed at a certain well-defined scale. Otherwise one will be stuck with increasingly bizarre speculations based on a wishful thinking. The hen cartoon is right: if you're chasing a new visible island of new physics that has to be visible from your place, you will lose the sense of direction and your search will be chaotic and unguided. Look at Jester's words:
So, while pushing up the energy frontier in accelerators will continue, I think that currently searching high and low for a new scale is the top priority. ...
He wants to guess the kingdom of the new scale and its princess from some higher-dimension operators such as\[

\frac{1}{\Lambda^2}(\bar s\gamma_\rho b) (\bar \mu \gamma^\rho \mu).

\] It's a fact that you're not guaranteed to find anything at any particular scale. It's like looking at the Atlantic Ocean with your binoculars. Are you guaranteed to see hints of a new continent, America? Isn't it better to be more courageous and abandon the totally unjustified assumption that your left leg should permanently stand on the Iberian peninsula? Columbus did so. His group was sailing for a few thousand kilometers – he didn't exactly know how much was needed – and he discovered a new continent. Chances are that you can't discover a new important land without getting wet!

Just to be sure, I think it's slightly more likely than not that SUSY will be discovered at the LHC in 2015 and the probability is comparable to one-half that the dark matter underground experiments will agree about a dark matter particle. But none of these probabilities is "well above 99 percent", for example. Indeed, we're not guaranteed that any particular experiment will discover these new things. There's no scientific or rational reason why we should be guaranteed that. And there's no reason for science to stop just because we're not guaranteed such things.

Again, it's time for HEP non-experimenters to (at least partially) switch to the top-down thinking unless they want to increasingly resemble the headless hens.


  1. Somebody stop me!!! When I hear these things about the wavefunctions and whatever Sean Carroll says I just see red in front of me! The fact that wavefunctions can be negative but in order to calculate the probabilities we have to square them is just a principle of quantum mechanics. That cannot possibly tell us that "wavefunctions are real" and they are NOT, at least not in the sense of "waves on the surface of water". Unitarity? Ok, let's say you invent all the parallel universe idea just to keep unitarity, but so do ghost fields in QFT and nobody ever said "ghosts are real" (at least as far as I know). Quantum mechanics refers to probabilities so when you measure something you don't have probabilities, you have the outcome of the measurement. Take a spin, you don't know its orientation. You measure it: it's up with respect to your aparatus. Ok, now if you measure it again it will continue to be up because this is how it is. Before measuring it there was no given state for the spin (how could it have been? your aparatus might have been rotated in whatever reference frame, it would be absurd to assume the electron knew how you orient your aparatus. So, obviously, after one measurement you get one result but the probability of that outcome is given by the wavefunction which is just an "interpretation" about whatever we can know about reality. It becomes something else after we know something else about reality. It is more or less the same thing with the change of the field representation of a theory in QFT. You may add extra fields, integrate over some others, change the theory accordingly, add ghosts etc. but you don't change "nature" by this, just the way you describe it. Ok, maybe I say some things wrong here because of getting really annoyed but I just have to say this about this Sean Carroll... He is just propagating nonsense. Ok, feel free to delete my post or correct whatever is wrong.

  2. "I am still not aware of any popular presentation of the foundations of quantum mechanics that is done right."
    Does this mean that you know of a non-popular one that is done right ? I would be very interested know which one that is.


  3. On the contrary, I agree with you entirely.

  4. OK, I really meant that Dirac's introductory textbooks to QM were pretty much right about everything. They're not modern in the strictly temporal sense, however, and they can't be used to understand why all the later added interpretational crap is crap.

  5. John Gribbin's In Search of Schrödinger's Cat is a popular presentation of the Copenhagen Interpretation. (Unfortunately, in the sequel, Schrödinger's Kittens, he is far less sensible)

    As for you comments re jester, well, not many people are gonna be interested if your theory makes no observable prediction (that can't be explained by existing theory), so you'll just sound like some crazy religious prophet as the years pass (Even if String Theory is the correct description of microscopic nature)

  6. Finding out what is "real" and what not is an important task. In mathematics (topology) if one proves that two spaces are isomorphic one says they are the same so one cannot say one "invented" a new space, isomorphic with X... This concept is extremely useful in other theories as well (see mirror symmetry, which I now try to understand in more detail) where theories (spaces) can be shown to be isomorphic and related by some transformations. It is a huge problem if someone starts giving attributes like "reality" to all sort of nonsense as does this "element" there... people (mainly students) will be highly confused about what is part of the mathematical aparatus and what is "really real"... One should really stop inventing all sort of nonsense...
    By the way, the measurement "problem"... just read some papers where they say they "disproved" Heisenberg saying that it is not "measurement" the origin of quantum uncertainity... I was like d'oh! Well, who on earth said it was?? It is that nice thing called non-commutativity of operators or incompatible operators (or other names one can give to the idea) that impose upon us uncertainity. I don't remember the name of the author but he said something like he has to rewrite his course notes! Do you imagine someone teaching that kind of stuff in a university? And then students come and ask us something and when we say it's nonsense they say "no, my prof. is an idiot, genius Sean Carroll said differently, and he is right" .... yeah, right!

  7. Did you mean "homeomorphic"? "Isomorphism" depends on the category you are considering, hence in topology is homeomorphism, in homotopy theory "homotopy equivalence", etc.

  8. thanks, you are of course right! :) I was speaking a bit "metaphorically" too, but I am glad there are some careful observers... I like this blog more and more...

  9. Thanks, I agree they are great.
    "... all the later added interpretational crap is crap." Yes, it has added substantially nothing (yet?), it seems.

  10. I haven’t looked the details but from the discussion part I
    think Marolf must be on drugs or something. He says:

    “Thus our work here strengthens the argument that any UV complete theory of gravity will be holographic, even if it contains no strings”.

    Mr Marolf do you know many such theories? The only one I know is String theory and demonstrates the Holographic principle explicitly.

    How many UV complete theories of Gravity are out there? As the highlanders it could be only one…

  11. Lubos, the world awaits your popularized optimal overview of the probabilistic properties of the multiverse!

    I expect yours will so evenly pivot the truth (about fundamental physical reality) or be so extremely balanced and to-the-point about these matters that it will be perceived as a threat by people (including professional physicists) who have settled on and gotten to feel secure with a comparatively sloppy and skewed reasoning about the same aspects of reality; However, as is often the case: "No pain no gain"!

    Moreover, I would not bet against that your potential (eventually published to a broader audience?) overview would not be exquisitely playful too! :-)

    The bigger the audience for your texts (those with only a light amount of LaTeX) the better, IMO.

  12. "buy the book on the electroweak theory by my major undergraduate QFT instructor" Could you specify this reference, please?

  13. It's the image-based picture on the left side. Did you turn iframes off or something like that?

    Or search Jiri Horejsi at

  14. I dont know why this is, but I cant even read quantum interpretation stuff, my mind regularly shuts down when I try ... :-D

    The same goes for contrieved philosophical babling etc ...

  15. Your view of QM is the same as mine and, therefore, it is entirely correct!

  16. Lubos, what do you make of Maldacena saying: "spooky action at a distance creates space-time"?

  17. I found "The Structure and Interpretation of Quantum Mechanics" by R.I.G. Hughes to be a good layman's introduction. His writing style is very engaging as well. His background is in philosophy (which I know Lubos doesn't like) as well as physics, but he seems unusually clear headed for a philosopher.

  18. Dear Justin, I am certain that he means nothing evil at all, just a translation of the ER-EPR correspondence of his and Susskind (which I am totally convinced is right)

    to "popular English". The spacetime is the non-traversable black hole in their picture; "spooky action at a distance" is Einstein's *exact* synonym for the quantum entanglement. The synonym reflects Einstein's own misunderstanding how the world should work - he believed that any prediction from quantum entanglement is ultimately wrong in Nature - but that changes nothing about the content of the whole phrase which means nothing else than quantum entanglement even though quantum entanglement isn't too spooky and isn't transmitting any information at a distance.

  19. Here's another way to begin thinking about the firewall paradox. Imagine a pirouetting dancer in front a mirror. The dancer and her mirror image are analogous to entangled pairs [1]. The mirrored dancer exists in a mirror space that can be distorted, analogous to a the distorted metric around a blackhole. Parity conservation is initially assumed to be true in the creation of these "entangled" dancers, although it is well known that in weak interactions parity is not conserved [2].

    In the firewall paradox argument, we can think of the mirror space that contains the mirror image of the dancer to become gradually more distorted, eventually becoming so distorted the image is no longer discernible. Conventionally, the mirror space might return to a non-distorted state, and the original mirror image of the dancer might not be decipherable, but it is not gone. The firewall argument is concerned about the possible independent evolution of the mirror-dancer when the mirror is in its completely distorted state. The argument is that if we were to potentially decipher the mirror image, it might not resemble the dancer. The situation is akin to a movie-like situation of staring into a mirror and seeing the reflection of someone else. The firewall brutally prevents this by destroying the mirror-image when the mirror becomes distorted with a violent interaction with random transformations, thereby making sure the mirror-dancer is never decipherable.

    The ER=EPR argument is essentially one that allows for mirrored evolution of the dancer and her mirror dancer. It allows for the distorted evolution of the dancer, but this will always be in lock-step with the evolution of dancer. If the dancer and ever sees a deciphered mirror-dancer, they will always look the same, despite the continued evolution. This is analogous to the dancer looking into the mirror to see her aged self.

    The ER=EPR argument is certainly superior to the firewall situation, which assumes the ability to generate random transformations. In a fully deterministic evolution of the wave function in Hilbert space, the random transformations are not feasible. However, specific state function evolution is governed by the mass term, and mass is largely the result of chiral symmetry breaking [3]. Further, we know that CP-violation is also possible [4]. This leaves us in some unsettling speculation that in situations were we are talking about massive systems, it is possible that the mirror-dancer might not have been exactly like the dancer when they were created in the first place. This means that they were in a mixed state to begin with.

    From this train of thought, one might begin to see that the firewall paradox as proposed is a math problem and not a physical problem. If that is the case, then the question is whether it is possible to assume pure states as initial states to begin with when dealing with massive systems. I am not entirely sure.