Brane Waves

The first day of the conference celebrating theoretical physicist Joe Polchinski (see also yesterday’s post) emphasized the broad impact of his research career.  Thursday’s talks, some on quantum gravity and others on quantum field theory, were given by

  • Juan Maldacena, on his latest thinking on the relation between gravity, geometry and the entropy of quantum entanglement;
  • Igor Klebanov, on some fascinating work in which new relations have been found between some simple quantum field theories and a very poorly understood and exotic theory, known as Vassiliev theory (a theory that has more fields than a field theory but fewer than a string theory);
  • Raphael Bousso, on his recent attempts to prove the so-called “covariant entropy bound”, another relation between entropy and geometry, that Bousso conjectured over a decade ago;
  • Henrietta Elvang, on the resolution of a puzzle involving the relation between a supersymmetric field theory and a gravitational description of that same theory;
  • Nima Arkani-Hamed, about his work on the amplituhedron, a set of geometric objects that allow for the computation of particle scattering in various quantum field theories (and who related how one of Polchinski’s papers on quantum field theory was crucial in convincing him to stay in the field of high-energy physics);
  • Yours truly, in which I quickly reviewed my papers with Polchinski relating string theory and quantum field theory, emphasizing what an amazing experience it is to work with him; then I spoke briefly about my most recent Large Hadron Collider [LHC] research (#1,#2), and concluded with some provocative remarks about what it would mean if the LHC, having found the last missing particle of the Standard Model (i.e. the Higgs particle), finds nothing more.

The lectures have been recorded, so you will soon be able to find them at the KITP site and listen to any that interest you.

There were also two panel discussions. One was about the tremendous impact of Polchinski’s 1995 work on D-branes on quantum field theory (including particle physics, nuclear physics and condensed matter physics), on quantum gravity (especially through black hole physics), on several branches of mathematics, and on string theory. It’s worth noting that every talk listed above was directly or indirectly affected by D-branes, a trend which will continue in most of Friday’s talks.  There was also a rather hilarious panel involving his former graduate students, who spoke about what it was like to have Polchinski as an advisor. (Sorry, but the very funny stories told at the evening banquet were not recorded. [And don’t ask me about them, because I’m not telling.])

Let me relate one thing that Eric Gimon, one of Polchinski’s former students, had to say during the student panel. Gimon, a former collaborator of mine, left academia some time ago and now works in the private sector. When it was his turn to speak, he asked, rhetorically, “So, how does calculating partition functions in K3 orientifolds” (which is part of what Gimon did as a graduate student) “prepare you for the real world?” How indeed, you may wonder. His answer: “A sense of pertinence.” In other words, an ability to recognize which aspects of a puzzle or problem are nothing but distracting details, and which ones really matter and deserve your attention. It struck me as an elegant expression of what it means to be a physicist.

28 thoughts on “Brane Waves”

  1. With that last comment about being prepared about working in the real world, I would like to say that I am proud to have worked for over 30 years in the service and construction industry doing useful things that people can see the results of.

    I think there is a real side to physics (of course) but also an unreal side of dreamed up theoretical stuff that is more fantastic than some of the BS stories some of the older construction workers tell newbies just for kicks.

  2. What to do if the sense of pertinence differs from one physicist to another? I mean, do we vote to determine the rightness of pertinence and determine it by majority? Do you think that following the current fashion is the latest scientific word in favor of rightness? Don’t we have to encourage and support the variety of directions?

    • Not everyone will agree about what is pertinent; but the notion that the key to effective reasoning is to find and focus on the pertinent is common to good logical reasoning, which is critical in science.

      • I agree, but I am afraid the “critical mass” (mainstream) eliminates (no funds) the minimum of opinion diversity. The latter is more important for a healthy science development. Brane waves, what a very pertinent direction!

  3. The sense of pertinence is also important in chemistry, especially when you are trying to dissect the effects of different chemical properties on an observable (drug activity, solar cell efficiency, polymer conductivity etc.). Knowing which properties are unimportant and which ones may be the causal ones using a mix of modeling, theory and experiment characterizes much of chemistry research.

  4. Wow, I saw your ‘debate’ with Gross at the end of your talk. Well done! You managed to hold your (very reasonable) ground well, I thought. About time someone said it straight to these guys.

      • Strassler says: hey, time to consider that the LHC results are circumstantial evidence AGAINST STRING THEORY, and for the SM.

        Gross: but moving to higher E colliders is a no brainer for progress by the reductionist thinking of modern science.

        Strassler: I’m not saying there is no argument for a new collider, just that a wider range of possibilities might exist. Recall Michelson-Morley and the tests that were NOT being done at the time, because no one had conceived of Special Rel.

        Gross: bla bla …

        Strassler: For example, sterile neutrino Dark Matter is a possibility outside the String paradigm.

        Gross: silence.

        • Well — now, that’s putting words in (and taking words out) of Gross’s mouth. It’s best to listen to the exchange. In any case, I was trying to shake up the system a little bit and make sure people think carefully about the future of our field, rather than letting inertia take over.

  5. Hie Matt

    I am happy to inform you and those like me who love to discuss Quantum Gravity on your blog that my paper on quantum gravity entitled the Nexus Graviton: A Quantum of Dark Matter and Dark Energy has passed the stringent peer review process of the International Journal of Geometric Methods in Modern Physics (IJGMMP) and is due for publication by the end of March or early April.

  6. We live in a world of extreme inequalities 🙁 and contradiction where that ability plays a vital role. In the KITP site there is public lesson of Joe Polchinski and I love the slide where he’s showing Maxwell’s predictions and Hertz’s confirmation, 25 years later. Looking back at 1995 time is ticking away 🙂

      • “Direct observation” requires qualification. First one needs to think hard and find the appropriate experiment-and the appropriate framework: the Z-boson was “indirectly” observed in 1973, through the discovery of “neutral currents”, in the Gargamelle experiment at CERN. New experimental techniques led to its “direct” observation in 1983, but the discovery of neutral currents was a milestone. From that point on it was understood that the Z-boson *must* exist, so the problem of finding it could become much more focused.

        Thanks to the precise measurement of its properties then at LEP, it was possible to deduce the value of the mass of the top quark-before it was “directly” observed at Fermilab in 1995.

        The “direct observation” of gravitational waves is a very difficult problem-the backgrounds are horrendous and the detectors, like LIGO, VIRGO or (E)LISA are still being developed. Nevertheless, the measurement of the variation, over a ~20 year span, of the period of a binary pulsar by Hulse and Taylor was, rightly, honored by a Nobel Prize in Physics in 1993 as the “indirect” observation of gravitational waves.

        Finally, reading Michelson and Morley’s paper, what is, particularly, nice to realize is, precisely, how they understood what is the appropriate proxy for the effect they were looking for.

  7. Regarding the Michelson-Morley experiment, what’s interesting is that the “error bars” were, originally, hardly conclusive by themselves. It was the “theoretical” work by Poincaré and Einstein that gave confidence that more careful measurements would lead to an enhancement of the signal, rather than its disappearence. As Einstein stressed to Heisenberg after the latter’s seminar in Berlin (cf. Heisenberg’s “Physics and Beyond”) `ìt’s the theory that decides what’s to be observed.’ But this experiment, the culmination of careful measurements and refined techniques, also illustrates that “precise measurements at one scale, allow us to discover hints of new effects at other scales”. The paper by Michelson and Morley, cf. here is well worth reading.
    Regarding the LHC, we are, still, at the beginning. And we still have a lot to learn about supersymmetry and how it affects the Standard Model.

  8. Professor Elvang’s first name is spelled Henriette. However, it is pronounced such that the final syllable is a schwa, as for the erroneous spelling given above.

  9. Ah, yes, pertinence! As a (relatively) young scientist, I feel I still have a lot to learn about what questions are the best ones to ask, and I all too often have gotten bogged down in details that in retrospect weren’t really that important. So, indeed, this is an important ability to cultivate no matter what field of science one is in.

  10. I am trying to digest your is hard!I am interested in your comment baryons are just D- branes. What about quarks,gluons and leptons?I thought D-branes are extensions of one dimensional strings. How are you bypassing strings?

  11. Does anyone else frequently have difficulty with Juan’s talks? His papers are always crystal clear, but I’m often completely lost when he presents his material in a lecture format. The tensor network material sounds really interesting, I just don’t get it.

    • I have a bit of physics and math background and with Maldacena’s (and some others’) talks I have the paradoxical problem that there is too little math in them for me. He often uses intuitive arguments that only experienced theorists understand, I guess. If I can’t follow, I don’t even know what I don’t understand. 🙂 Maybe I should try the papers…

      • it’s the opposite for me. Most of the intuition is obvious and inline with what other experts are doing. Juan is setting up a system that is essentially like a toy model of a blackhole. The Hilbert space is truncated but it has all the features of what one expects from a well behaved horizon. The great benefit is that you can in principle calculate things in his setup and the problem in principle becomes mathematically tractable. His method presumably allows people to track the entanglement more precisely.

        This hasn’t been done yet, or at least he hasn’t shown it, but I think that’s the play. Of course I don’t understand how or why this is justified, why this shows a problem with AMPs argument (it seems to be a very special construction and not something that would be generic) and moreover I don’t know how to calculate with tensor networks.

  12. Doesn’t quantum entanglement indicate that there could, indeed, be an aether? Not necessarily a “medium”, like a field, but rather geometry, space.

    We perceive space as 3-dimensional because we can only “see” it as prescribed by predominantly quarks, the building blocks of our 3D world.

    Another way of asking the question (above) is, is space fundamental to everything, including the creations of fields? i.e. “nothingness” ~ homogeneous space, which can only exist instantaneously because of chaos. So, it is the harmonics of space that create the field and associated “particles”. The “wave” is merely a manifestation of the space continuum, composed of curved conduits all connected, an infinite dimensional Mobius strip. And the dimensions we live in are the fundamental harmonics of space.

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