Strings 2015

Strings 2015 gets underway in Bangalore tomorrow, and so far the press coverage I’ve seen consists just of two articles that aren’t what I’d guess string theorists would like to see:

  • In The theory that may have been stringing scientists along for years Robert Matthews starts with

    Over the next few days, the southern Indian city of Bangalore will be playing host to an exclusive group of people.

    No amount of money can buy you membership and it doesn’t matter how well connected you are. But rumour has it that it helps if you have a brain the size of a planet.

    but soon moves on to

    There’s just one problem: there’s not a shred of evidence to support it. And that is now leading to awkward questions about just what all these very smart people have been doing with their time and funding.

    He then goes on to discuss the recent New York Times Op-Ed, as well as a Physics Today piece

    The American Institute of Physics has now gone further, with an editorial in Physics Today asking if the insouciance of string theorists over the issue of testability may harm public faith in science.

    Finally, there’s an accurate discussion of the relation of string theory to the search for superpartners in Run 2 at the LHC

    The real fun and games will start if the particles are not found. That is because, even after all these years, string theory is not tied down very tightly.

    As a result, theorists can tweak their equations to explain away the failure.

    Such flexibility is a classic symptom of pseudo-science, and it is what particularly irks physicists about string theory – along with the arrogance of some of its practitioners, who insist it is the only way to complete Einstein’s quest.

    But there is another source of resentment, and one with which we can all sympathise: that an entire generation of brilliant minds may have been lost to an esoteric mind-game.

  • The other string theory news story is at The Telegraph, a Calcutta paper, which has Physicists too can have fun. The article is about Ashoke Sen’s bizarre hep-th article Riding Away from Doomsday, which was the topic of an April 1 posting here. Since then, Sen has shot down any idea that this was a hoax, and has turned it into a major research program, with a technical hep-th article and a talk scheduled for the opening session of the conference tomorrow. The article argues for the importance of computing the decay rate of the universe since it

    is important for planning our future course of action if we are to adapt this strategy for increasing the life expectancy of the human race.

    String theory is supposed to provide this calculation, but Sen characterizes the status of that calculation with

    it is probably fair to say that we do not yet have a definite result based on which we can plan our future course of action.

    which shows that, despite what some people say, he definitely has a sense of humor.

Given press coverage debating whether string landscape research is pseudo-science or a joke, I wonder what prominent string theorists gathered in Bangalore now think of the string theory community’s decision over the last ten years to mostly go along with the idea of the string landscape as an excuse for why string theory predicts nothing. This all started about ten years ago, and it’s interesting to take a look again at the panel discussion at Strings 2005, where the panelists were in favor of the landscape, but the audience not so much. The last ten years have shown conclusively that any hopes for predictive science coming out of the landscape were misguided, but will that or bad press cause anyone to re-evaluate their stand on this?

Update: Slides of the talks are appearing here. One of them is so interesting I’ll devote a posting to it…

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16 Responses to Strings 2015

  1. Bernhard says:

    ” Since then, Sen has shot down any idea that this was a hoax.” Wow, it seems one get away with really anything these days in theoretical physics once you’re on top enough. HEP-TH, the official laughing stock of science.

  2. South Park is brilliant says:

    It’s just not true that “There’s just one problem: there’s not a shred of evidence to support it.” It is a consistent unification of quantum mechanics and gravity. That in itself is evidence that it is on the right track.

  3. Dave Miller in Sacramento says:

    SPib wrote:

    It is a consistent unification of quantum mechanics and gravity. That in itself is evidence that it is on the right track.

    But does the theory actually exist? Can you actually write down any non-trivial solutions?

    You know the widely accepted claims that phi-to-the-fourth theory does not actually exist in 4D (i.e., except as the trivial free theory)? Do you have any evidence that something of the sort is not true for superstring theory?

    For that matter, can you even write down the equations for the mysterious M-the0ry that supposedly is the reality behind strings?

    These are not rhetorical questions: I am not as critical of string theory as Peter is. If nothing else, solely as a matter of mathematical curiosity, I would like to know the answers to these questions.

    Can you answer any of them?

    Dave Miller in Sacramento

  4. Peter Woit says:

    Please resist trying to have the same tired arguments about string theory. At this point, anyone who argues that “string theory is a consistent theory” has long ago heard that the problem “what is string theory?” has not yet been solved, but decided that there’s no contradiction between something not being well-defined and its being consistent.
    20 years ago, this kind of thing was the problem with arguments for string theory. Things are different and much worse now, with the move to the string landscape pseudoscience/joke.

  5. Jonas says:

    It is an experience of life that whenever persons start talking or writing about the end of the world/universe/civilisation – like Sen is doing – it is because they are feeling their own end approaching. One should be kind and understanding to the person, and at the same time ignore the topic and arguments.

    After all, previous experience can be seen to imply that the world/universe/civilisation survives the death of single humans.

    But who knows; maybe the person is right this time?

  6. Visitor says:

    “The American Institute of Physics has now gone further, [. . . ] asking if the insouciance of string theorists over the issue of testability may harm public faith in science.”

    Speaking strictly for myself, as a non-scientist, I can say that their concern in misplaced – slightly. My attitude towards science has not changed. My faith in scientists, however, is greatly diminished. (Although this is not solely because of string theory and multiverse mania; the last decade and a half has seen accelerated trends that, along with the growth of “science of a new type”, compel me to realize that scientists are as venal and corrupt as the rest of modern society.)

  7. Dave Miller in Sacramento says:

    Although, Peter, maybe someday someone actually will come up with a non-trivial solution to string theory, or a set of definite equations for M-theory or whatever! And, I (and I suspect you yourself) would find that event quite interesting.


  8. Giotis says:

    Special attention to Gaberdiel talk.

    There is a modest revolution going on for some time now regarding the underlying symmetries of String theory.

    This revolution encompasses AdS/CFT and Higher Spin HS/CFT dualities.
    Roughly the picture is like this:

    As it is well known String theory besides its massless sector has an infinity number of massive higher spin fields. These fields are distributed in various trajectories (so called Regge trajectories) based on the relation between the mass and the spin of each field. The leading Regge trajectory is the one with the lowest mass for a given Spin. At its tensionless limits these massive fields become massless and it is generally expected that at this limit String theory will possess a huge underlying symmetry.

    Now Higher Spin theories on AdS spaces pioneered by Vasiliev have an infinity number of massless Higher Spin fields too and thus posses a Higher Spin gauge Symmetry. This higher Spin gauge theory includes the spin 2 graviton and generalizes pure gravity in AdS. This basically means that the underlying space possesses a higher space time symmetry which by gauging it gives rise to the higher spin gauge theory much like gauging Poincare symmetry gives rise to pure gravity.
    The general expectation is that this higher spin symmetry is a closed subsector of the bigger underlying symmetry of String theory at its Tensionless limit. The higher spin fields of Vasiliev’s HS gravity theory should correspond to the higher spin fields of the leading Regge trajectory of String theory.

    Now via a Higgs like phenomenon this huge symmetry of String theory is broken and Tension is introduced, as a consequence the higher spin string fields become massive.

    The goal is to verify these general expectations and analyze the higher underlying symmetry of string theory using these facts.

    For this you can use AdS/CFT by embedding HS/CFT dualities to Stringy AdS/CFT dualities.

    Generally speaking an interacting Vasiliev’s HS theory is dual to a free CFT on the boundary where the ‘t Hooft coupling is zero but N is large.

    The conserved HS currents of the free CFT correspond to higher spin gauge fields in the bulk.

    For example in AdS₄/CFT₃ Klebanov-Polyakov famously conjectured (and later verified by others) that there is a duality between a vector like CFT (and not a Matrix like in Yang Mills theories) and Vasiliev’s HS theory in the AdS₄ bulk. Then you can try embedding this HS duality in String theory dualities.

    The famous ABJ triality paper for AdS4/CFT3 and Gopakumar Gaberdiel work on AdS3/CFT2 are very important in that respect.

    ABJ Triality: from Higher Spin Fields to Strings:

    Higher Spins & Strings:

    and subsequent work

  9. nicola says:

    The title of Witten’s talk is really something “What Every Physicist Should Know About String Theory”. So we learn that every physicist should actually know string theory. That’s really funny!

  10. Peter Donnelly says:

    I had to look up “insouciance”. It means “casual indifference”.

    Very apt.

  11. paddy says:

    Sorry but todays featured article on Wikipedia is…(drum roll) …M-theory. Thus it must be defined….nicht wahr? 🙂

  12. Peter Woit says:

    I notice in that very long article, no space at all is found to discuss what the problems with the idea of M-theory as the TOE are. All I see is one sentence saying that “some” criticize the idea. At least the single source given in the footnote is one I can’t argue with…

  13. Jan Reimers says:

    Nima’s slides appear to be full of SUSY optimism: here

    – LHC run #2:
    1 SUSY even per minute,
    100 times the particle production of run 1 (because E^4 in cross section),
    100 fb^-1 by 2017, which is enough to discover a <=1.8TeV gluiono ot <=1TeV stop.
    – Q: Should we be worried/depressed about prospects for low-E susy after run #1?
    A: Not much more worried that we should have been (were!) after LEP II.
    – There is a "Why no SUSY @ LEP" slide that I cannot understand.
    – Naturalness: Not problems – Opportunities (Thankfully no mention of multiverse!)
    – He mentions something called "Compulsory Natural SUSY" which apparently gives better unification of the (3) coupling constants than does "Natrual SUSY".
    – He is pushing for a 100TeV ring and a Higgs Factory. We need these to map out the Higgs potential.

    Of course no mention of strings.

  14. Steamy Ray Vaughn says:

    Peter, just some information that may be of interest:

    At Strings 2015 Nima Arkani-Hamed gave a talk ‘Collider Physics at the LHC and Beyond’ and said, about finding supersymmetry: “we should always be looking for it” 59:28, and “we could just be unlucky and miss it” [at the LHC] 59:49.

    I take this to mean he believes there is >50% chance we’ll find something at the LHC.

    If I understood correctly, not finding supersymmetry at the LHC would only mean adjusting parameters by 1%.

  15. Peter Woit says:

    (moved your comment to more appropriate posting).

    I took a look at the Arkani-Hamed talk, didn’t see anywhere he said he believes better than 50% chance of SUSY at the LHC. He says the multiverse is still the best explanation around, and has nothing new about SUSY: according to “naturalness” arguments you were supposed to see it at the Tevatron or LEP. By the same arguments you could say there was still one chance in 10 that it was at higher energy, so would show up at the LHC. All he’s saying is that if you don’t see it at the LHC, you can keep playing the same game as for the last 20 years and say there’s one chance in 100 (1% tuning) that it is at higher energy. He’s spent much of his life on SUSY models, so thinks looking for SUSY is a good argument for a 100 TeV accelerator. I don’t think so, instead the LHC will have provided extremely strong (99 to 1) proof that a not very good idea that didn’t explain much really doesn’t do what you wanted it to.

    The more interesting things about the talk I thought were:
    1. Despite being at a string theory conference, no mention of strings. For a 100 TeV machine he’s not going to even try the “maybe we’ll see strings and extra dimensions” argument that many used for the LHC.
    2. The serious question for a next generation machine is about what it would tell us about the Higgs, and that was much of his talk.

  16. nicola says:

    Is there any way to see Witten’s 2nd talk. It’s not here

    I didn’t know that every physicist should know anything about ST so I’m curious what he meant.

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