Quick Links

Posted on August 13, 2013 by woit
  • At HEP blogs you should be reading already, there’s Tommaso Dorigo on 5 sigma (with more promised to come), and Jester on the lack of a definite BSM energy scale. Jester puts his finger on the big problem facing HEP physics. In the past new machines could be justified since we could point to new phenomena that pretty much had to turn up in the energy range being opened up by the machine (Ws and Zs at the SPS, the top at the Tevatron, the Higgs at the LHC). Now though, there’s nothing definite to point to as likely to show up at the energy scale of a plausible next machine. Jester includes a graphic from a recent Savas Dimopoulos talk characterizing the current situation in terms of chickens running around with their heads cut off, which seems about right.
  • The black hole information paradox has been around for nearly forty years, with the story 10 years ago that it supposedly had been resolved by AdS/CFT and string theory. For the past year or so arguments have been raging about “firewalls” and a version 2.0 of the paradox, which evidently now is not resolved by AdS/CFT and string theory. I couldn’t tell if there was much to this argument, but the fact that there’s a Lubos rant about how it’s all nonsense made me think maybe there really is something to it. As usual though, my interest in quantum gravity questions that have nothing to say about unification is limited. For those with more interest in this, I’ll just point to today’s big article in the New York Times, and next week’s workshop at KITP where the latest iterations will get hashed out. For more on the challenge this argument poses to the idea that AdS/CFT gives a consistent picture of quantum gravity, see this recent talk by Polchinski.
  • For another challenge to orthodoxy from someone at UCSB, Don Marolf has a new preprint out arguing that strings are not needed to understand holography:

    Stringy bulk degrees of freedom are not required and play little role even when they exist.

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9 Responses to Quick Links

  1. David Appell says:
    August 13, 2013 at 10:44 pm

    Is it just me, or does Leonard Susskind not possess a curious ability to get into the media no matter is the physics topic du jour?

  2. Lun says:
    August 13, 2013 at 11:35 pm

    The strong version of ads/Cft must be stringy as you need two expansion parameters, the number of colors and the coupling constant.
    In the planar limit this is however irrelevant, it seems that in that limit (where most on the evidence for holography comes from) such arguments could apply.
    The firewall debate, with neither a sliver or experimental connection nor anything approaching rigor or a coherent picture, is a good example of what’s wrong with modern physics.

  3. Oldster says:
    August 13, 2013 at 11:46 pm

    David: Leonard Susskind is an outgoing, intelligent, personable guy who has been in the thick of the information paradox and string theory scene for decades, and who likes to write and comment for the public as well. No matter what your views on the physics, it would have been hard to avoid his name in this particular story. I say this as someone who is a hopeless reactionary compared to him on physics too, not as an advocate … 😉

  4. Peter Shor says:
    August 14, 2013 at 8:36 am

    Leonard Susskind gives excellent talks, is a great teacher, and enjoys talking to the public and the media. This is undoubtedly one reason why reporters like him; they find him eager to talk to them, and they can understand him.

    I don’t think he’s beating on the media’s doors and asking them to write stories about him, the way I suspect some other physicists are doing.

  5. Anonyrat says:
    August 14, 2013 at 11:30 pm

    Is Don Marolf’s argument essentially that a theory with diffeomorphism invariance has an action whose significant terms are boundary terms, and hence has a form of holography?

  6. Mitchell Porter says:
    August 15, 2013 at 1:33 am

    I am still digesting Marolf’s paper but it seems a little dodgy. It does not talk about holographic *duality* at all – i.e. the equivalence between a theory in the bulk and another theory on the boundary. Instead, it is (I think) an argument that a general quantum state in the bulk theory can be constructed just using bulk operators from the boundary.

    To understand what that means, we need to distinguish between operators in a separate theory defined on the boundary, as in AdS/CFT, and operators in the bulk theory which pertain to bulk observables near the boundary. In the latter case we are talking only about one theory, called the bulk theory, but we concern ourselves with operators in that theory which are associated with the edge of the bulk.

    Marolf also uses the Reeh-Schlieder theorem, a well-known theorem from algebraic/constructive/axiomatic QFT which says that, because of the entanglement of the vacuum state, any state in the QFT can be approximated arbitrarily closely, by combinations of operators from arbitrarily small spatial regions. He then combines this with special properties of gravitational theories (I haven’t decoded that part) to deduce a property he calls “information holography”.

    As a non-expert observer, what I notice is that there have been at least two other attempts to apply Haag-like models of QFT to AdS/CFT which have come up wanting. Both were debunked by Jacques Distler: first, years ago, Rehren’s “algebraic holography”, which Distler dubbed “Rehren duality” to distinguish it from the real thing, and then, much more recently, Gomes et al (arxiv:/1305.6315), who proposed to explain the emergence of gravity from the RG flow on the boundary by using the “shape dynamics” formulation of general relativity. But it will take someone better than me to say exactly what the status of Marolf’s paper is.

  7. ohwilleke says:
    August 15, 2013 at 5:26 pm

    “Is it just me, or does Leonard Susskind not possess a curious ability to get into the media no matter is the physics topic du jour?”

    One of the lessons that I learned in student government as an undergraduate and then a law student (and then again later during a brief stint as a professional journalist), is that the vast majority of people, even prominent people in politics or at the top of their fields, are extremely reluctant to talk to reporters (and not necessarily without good reason, I should add). Despite not having an official PR position, I ended up in the student newspaper almost every week in student government related stories simply because the reporters couldn’t find anyone else who would reliably provide them with quotable quotes for their stories. Later, as a reporter, the lazy thing to do was always to call people who I knew would be willing to go on the record for me when I wanted a quote.

    If you are among the 5% or so of prominent people in a field who are willing to go on the record with a statement about something on short notice and say something quotable when you do, reporters will flock to your door. Susskind and science reporters have mutually discovered this fact.

  8. Tommaso says:
    August 17, 2013 at 2:35 pm

    Hello Peter,

    thanks for the mention of my article on the 5-sigma criterion, of which I issued today the third (out of 4) part. I believe it is an important thing that we realize how that criterion has strong limits and should only be thought of as a guideline, not as a fixed rule.

    Best,
    Tommaso

  9. Peter Woit says:
    August 17, 2013 at 2:52 pm

    Tommaso,

    Wonderful series of posts. You’re doing a great job of not just explaining the “5 sigma” issue, but more generally giving a lot of insight into the subtleties involved in any search for a bump in an HEP experiment. Very educational.

    My own amateur, much cruder, take on these issues has generally been to not believe discovery claims made by one experiment, no matter how many sigma they say. If their competitor says they also see the same thing, that’s the time to start becoming a believer…

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