The latest press release hyping a string theory paper in a misleading way comes from my alma mater Princeton, which I find quite depressing. According to yesterday’s press release, entitled Princeton physicists connect string theory with established physics:
String theory, simultaneously one of the most promising and controversial ideas in modern physics, may be more capable of helping probe the inner workings of subatomic particles than was previously thought, according to a team of Princeton University scientists.
The theory has been highly praised by some physicists for its potential to forge the long-sought link between gravity and the forces that dominate within the atomic nucleus. But the theory — which posits that all subatomic particles are actually tiny “strings” that vibrate in different ways — has also drawn criticism for being untestable in the laboratory, and perhaps impossible to connect with real-world phenomena.
However, the Princeton researchers have found new mathematical evidence that some of string theory’s predictions mesh closely with those of a well-respected body of physics called “gauge theory,” …
This has nothing to do with the controversial failed project of using string theory to provide a unified theory of particle physics and gravity. What it is about is another check of something not very controversial at all: the pretty much universally believed idea that a very special un-physical quantum field theory, N=4 supersymmetric Yang-Mills theory, at strong coupling can be described by a weakly-interacting string. This AdS/CFT correspondence is now almost ten years old and a significant amount of evidence for it has accumulated. What the press release is referring to is this paper by Igor Klebanov and collaborators, which studies numerically an integral equation derived in this paper.
The press release has already led to stories here and here, with presumably many more to come. Should make Slashdot any moment now….
Maldacena’s unproved conjecture of a correspondence between 5-d AdS (anti de Sitter) space and 4-d stringy Yang-Mills conformal field theory (CFT) is one of the best things to come from string theory related research. I just love the fact that by the holographic principle, that 4-d particle physics resides as a brane or surface on a 5-d anti de Sitter space.
On the negative side,
*AdS has a negative cosmological constant, instead of a positive one,
*N=4 Yang-Mills CFT isn’t consistent with 10-d supersymmetry.
Other conjectured unproved correspondences which can under limited conditions model real phenomena to some extent include:
*by using phlogiston theory, you can model combustion without oxidation, which was very handy at one time,
*by using caloric you can model heat without needing kinetic and radiation theories, again, a useful simplification at one time (Ca/KR correspondence)
*by using Ptolemy’s epicycles, you can actually model planetary motions in the solar system, which was simple for astrologers (Pt/SS correspondence)
*by using the FitzGerald-Lorentz aether you can model the contraction of moving bodies without needing special relativity, which is oh so useful for crackpots (FL/SR correspondence)
So the evidence of adS/CFT correspondence conjecture holding fairly well, implies that maybe people should start taking seriously other models that are similarly based on totally unphysical assumptions?
Something is better than nothing. With all this arbitrary mish-mash of ideas being thrown around maybe ideas may evolve to bring more meaning into the current fundamental physics discourse; until that time more raving and ranting…
Oh, and by the way, Peter, you still haven’t written anything substantial on Rep Theory and Particle Physics for the advanced undergrad. May we expect anything of that sort within the next several months?
Thank you for the exciting news. I think the numerical confirmation of Beisert’s inspired guess how a gauge theory in the asymptotically free high-energy limit is smoothly connected to a string theoretical description at lower energy is a tremendous step forward, well worth some publicity.
F., nobody –I think– doubts that this is interesting stuff. And potentially highly useful. Well deserving of publicity.
But when the main author says,
he’s clearly saying something untrue. Much is known about the strong interactions in the low energy regime, and there are a variety of tools that have been successfully used to describe them.
After all, if the above quote is true, then, how well do they fit the Roper resonance? Can they predict the masses of the meson and baryon decuplets? Or, more to the point, what is the ratio of the rho to proton masses in their theory?
I mean, can they really do what has never been done before, as they claim? Can they do better than lattice QCD, chiral effective models, QCD sum rules, as they claim? Bring on the numbers then, we are eager to check ’em.
The press release isn’t all hype. Consider the following:
This is not to say that string theory is likely to become accepted as an overall explanation of subatomic physics anytime soon. Klebanov’s team has found a bridge between established physics and a mathematical theory, which is only one step toward solid experimental proof that the world is actually constructed of tiny vibrating strings. And even this bridge applies to only one facet of gauge theory. Bridging this gap for other facets will be necessary to enable physicists to understand fundamentally the interiors of the protons and neutrons that make up the earth beneath our feet.
I think that’s fair enough. “Other facets” clearly refers to QCD.
F., could you please explain what do you mean as “asymptotically free high-energy limit”? I though that N=4 SYM was a finite theory…
What the press release is referring to is this paper by Igor Klebanov and collaborators, which studies numerically an integral equation derived in this paper
Both of the links lead to the same paper
you are right, of course. I am referring to:
“Beisert said that his team’s work provided a useful abstract proof of the transition between weak and strong interaction strength, but that numerical evidence had been lacking.
“The result of Klebanov’s group gives beautiful numerical evidence for the validity of our proposal,” ”
Actually, string theory already is a “unified theory of particle physics and gravity”; whether it is a correct description of reality is yet to be seen…
Other folks will also find it depressing that Princeton is Peter Woit’s alma mater. But the press release is exciting and Dr (!) Woit should be praised for promoting it.
Lubos Motl also objects to this story. On the grounds that somebody used the word “controversial” in connection with string theory.
By the way, LM has recently written a screed on the 2nd law of thermodynamics that is decidedly non-mainstream; borderline crackpot in fact. I mention this *not* to start another anti-LM tirade, *nor* to initiate a discussion on the 2nd law, but as a warning to those who, like me, previously thought that he always knows what he is talking about on technical issues of physics. Evidently he doesn’t. Oh well. We’ll just have to read his technical writings with a few more grains of salt.
Couple of week back I read the review of the Director’s Cut version of String Kings. It seems that the Director’s Cut version includes more scenes featuring a certain “man on the edge”.
[Somewhat off-topic, but I thought you may be one of only a handful of people to give an honest + critical feedback.]
What do you think is specifically important about the following works? (I’m assuming you may have perused through one of them in your academic studies; I apologize if you haven’t):
“Topology, Geometry and Quantum Field Theory: Proceedings of the 2002 Oxford Symposium in Honour of the 60th Birthday of Graeme Segal”
“Geometry, Topology and Quantum Field Theory (Fundamental Theories of Physics)”
– P. Bandyopadhyay
‘Actually, string theory already is a “unified theory of particle physics and gravity”; whether it is a correct description of reality is yet to be seen…’ – Kasper Olsen
It’s not even a unification of particle physics and gravity. It’s merely a unification of the (ill-founded in view of the landscape) speculation that string can model particle physics, with the speculation that by M-theory you can include gravitons. To call string theory a unification of particle physics and gravity is misleading hype. Maybe instead you should call it a unification of unphysical speculations about particles and gravity.
Saying that string is does unify particle physics and gravity, but then afterwards adding that it has not yet been shown to be the correct unification, is the cause of all the confusing hype problems. You need to be completely clear and call string a speculative unification scheme.
String theory does in fact unify particle physics and gravity into a consistent structure. This is not speculation. You are right that we cannot say at the present why the specific vacuum which corresponds to our universe is chosen. However, I think the defiinition of particle physics is more broad than just the Standard Model. Do you have any reasons within the bounds of quantum field theory for believing that the structure of the Standard Model is unique and no other vacuum structure is possible?
And what, exactly, it is that you can say at the present time? Does string theory predict susy or not? Does it predict extra dimensions or not? Does it predict light scalars or not? And what are the corresponding mass scales?
gunpowder & noodles wrote:
“By the way, LM has recently written a screed on the 2nd law of thermodynamics that is decidedly non-mainstream; borderline crackpot in fact.”
LM’s opinions on thermodynamics are about as accurate as his ones on computers, numerical analysis, and climate science. BS.
What we can say is that string theory provides a consistent unification of quantum mechanics and gravity. Supersymmetry and extra dimensions are generic predictions. The physical properties of the universe that we live in corresponds to a specific solution. In order to make predictions, this specific solution must be found first. When and if this solution is found, we may be able to say why this solution is selected. However, even in the absence of such a selection principle, this solution would allow us to completely describe the physics of the universe we live in. So, you should give string theorist/phenomenologist time to discover this solution. Then, and only then, will we be able to make specific predictions about our universe.
V., being on the right track to a consistent unification of quantum mechanics and GR is what most people would call an important research program. It is reasonable to expect that, if successful, such program will have a lot to say about particle physics — and gravity.
But saying that string theory does in fact unify particle physics and gravity is very different. It implies, among other things, that particle physics can be derived from ST. And also that there are concrete predictions for future experiments. I think it’s still quite far from that. There are interesting generic predictions from ST, as you say, that have actually motivated a lot of model building. But no specific ones, as far as I know, not even about orders of magnitude.
And then, the possibility cannot (so far) be logically excluded that even if particle physics and gravity actually are unified in nature, that unification is not ST.
I think that you’re missing the point. All V is saying is that string theory is a quantum theory of gravity which can incorporate gauge theories, etc. V is not arguing that it necessarily has anything to do with our universe (though, of course, it might) just that it successfully merges gravity and particle physics. Some people think that this fact alone alone is impressive. I’m not aware of any other research programme which can make this claim. The only thing which comes close is LQG which, of course, doesn’t predict anything about particle physics either.
string theory does in fact unify particle physics and gravity
I think it might at most unify particles and the graviton, which is different from unifying particles and gravity and very far from unifying particle physics to gravitation.
I think there should be define what we mean when we are talking about particle physics. Are we talking about all possible gauge theories in general or just the Standard Model gauge theory which describes our universe?
A not-quite-serious Saturday Evening post:
I agree, semantics seems to be a problem here. By particle physics I understand what is measured in particle accelerator (and cosmic rays) experiments. And which is, so far, perfectly well described by the SM (minus some technicalities).
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I know nothing about the second reference, but the first is the proceedings of a conference I attended honoring Graeme Segal on his 60th birthday. It contains his notes on conformal field theory, which is a very interesting document. Most of it is research-level articles, as usual a mixed bag. Some very interesting, some not. But definitely a document that is more aimed at experts, not so much an expository book.
And it doesn’t look like I’ll have time in the near future to write up anything at an undergraduate level. At the moment, still trying to understand relations between Langlands stuff, representation theory and QFT, as well as continuing to work on BRST. Next year I’ll be teaching our graduate course on representation theory for the full year, hope to find time to generate a better set of notes, covering a wider part of the subject.