Talks at UCF

This past weekend I was at the University of Central Florida, participating in a symposium organized by Costas Efthimiou of the physics department there. It was sponsored by two student organizations, the university’s Society of Physics Students and Campus Freethought Alliance. There were two speakers, Jim Gates and myself. I suspect that the organizers and many in the audience were hoping for some fireworks between Gates and myself, taking opposite sides on the controversy over string theory, but I fear that we disappointed them.

My talk was entitled The Challenge of Unifying Particle Physics, and my intention was to avoid spending much time going over the problems of string theory, since I’m pretty tired of that, and instead to try and explain to the audience some of the basic facts about symmetries, representations and quantum mechanics, together with an outline of the current state of efforts to unify physics. Gates gave a very general talk about particle physics, unification and string theory, featuring a lot of very impressive graphics he has developed as part of a multi-media course called Superstring Theory: The DNA of Reality.

In the end, there wasn’t that much for us to disagree about. My critique of string theory as a unified theory is based on the claim that the idea of using strings in 10d doesn’t work because the variety of possibilities for handling the extra 6 dimensions makes predictions impossible. Gates has always been skeptical about extra dimensions and wasn’t about to defend them, let alone the landscape. I take his general attitude to be similar to that of Warren Siegel, who he collaborated with in the past, and who explains his point of view here. Recently Gates has been very much interested in representation theory, in his case the representation theory of supersymmetry, where he and collaborators see fundamental problems still to be resolved, and have new ideas about using Clifford algebras to attack them. For one of their recent papers written from the more mathematical end of the problem, see here.

I very much enjoyed my time in Orlando; high points were getting to meet with and talk to some of the physics students there, meeting someone who sometimes comments here who came to the talk, and especially getting the chance to discuss things with Jim, who I found to be impressively knowledgeable and thoughtful about every topic that came up.

This entry was posted in Uncategorized. Bookmark the permalink.

17 Responses to Talks at UCF

  1. Anton says:

    Siegel has many funny parodies on his web site. The one I liked a lot is “THe Official String Blog”:

  2. A.J. says:

    Hey Peter,

    Out of curiosity, is there anything Siegel says in his research summary that you disagree with?

  3. woit says:


    There are lots of different things in Siegel’s research summary. On the whole I’d say his interests are just in a different direction than mine. Lots of questions about string theories and superspace, whereas I just think there are much more interesting things to think about, especially various aspects of gauge theory.

    I think Siegel gets it right that the 10 d string is a doomed idea about unification. I’d be willing to believe his work on 4d strings might someday lead to new insights into QCD. But I don’t see any evidence that different ideas about string theory are going to give any insight into unification, and I’m basically agnostic as to whether string theory is particularly useful as s theory of quantum gravity.

  4. Hendrik says:

    Dear Peter,

    Concerning the mathematical problems involved with obtaining a consistent SUSY QFT, you may be interested in the obstruction theorem of Kishimoto and Nakamura at Commun. Math. Phys. 159, 15–27 (1994). A strategy for circumventing this obstruction recently appeared in

  5. A.J. says:

    Hi Peter,

    I wasn’t expecting you to say anything about D=4 strings.
    But I was struck by how sober and even-handed Siegel’s general comments on string theory are. No excited language, no wild claims. This sort of thing was the norm in conversation when I was a physics grad student, but seems rather rare in the blogotub.
    As for conclusions about string theory, I personally tend towards Siegel’s 2nd option: There’s something vaguely right about string theory, but no reason to believe that the various models which have been written down are correct. For one thing, they strike me as far too geometrical. I just can’t bring myself to believe that our world is described by anything as neat and clean as a Calabi-Yau manifold, or a bunch of intersecting branes.

  6. Chris Oakley says:

    “Superstring Theory: The DNA of Reality” sounds a bit like “Superstrings are the language in which God wrote the world”. Presumably this was not one of the things you agreed about – ?

  7. Coin says:

    So, a question?

    This jumped out at me from Siegel’s research summary:

    In fact, the only property of string theory not found in particle theory is Dolen-Horn-Schmid duality, which states that summing poles in one channel gives the same result as summation in another channel. This is also the only experimentally verified result of string theory.

    I have to confess I don’t really understand this… well… at all. A quick hit on Google indicates only that “channels” apparently means “momentum channels”, whatever those are. However:

    One of the most common (and common for good reason) criticisms of String Theory floating around right now is that it hasn’t made any testable predictions. One of the running themes I’ve noticed reading blogs like this is seeing String Theory proponents offering up various results of String Theory as “predictions”, but those results turning out under analysis to not fairly qualify as such.

    Siegel carefully words his page in a way that seems to be almost intentionally avoiding calling the Doren-Horn-Schmid thing a “prediction”, and I imagine if it were easily classified as such it would have been brought up elsewhere. But as he describes it, it is a result which is (1) predicted by String Theory (2) predicted by string theory uniquely, or at least not predicted by “particle theory” (3) borne out by experiment. These three things are generally the conditions I would think of when judging whether a scientific theory has made a “prediction”. If it is a prediction, it certainly doesn’t sound like a large or significant one, but based on the limited information I have it certainly does seem to be better than nothing.

    What vaguely is this Doren-Horn-Schmid thing, if it’s not too much trouble to ask? Would you say that it qualifies as a “prediction” made by String Theory? If not, why not?

  8. Doug says:


    I just want to commend you for your efforts to shed light on this highly specialized subject. You seem to appreciate how difficult it is for non-specialists to grasp what is going on, and are willing to use your gift for clear articulation to help out.

    However, your last slide is most revealing:

    1) The math of the SM is poorly understood in many ways.
    2) We don’t understand the representation theory of gauge groups.
    3) Future progress might require unification of mathematics.

    What are the chances that you are willing to prepare a talk elaborating on those three points?

  9. woit says:


    What Siegel is talking about concerns the idea of using strings to model the strong interactions. This goes back to the late sixties, early seventies, and there are good reasons to believe this is sensible. Some observed aspects of the strong interactions do appear to be well-described by a string model (but no one has a completely successful model). This has nothing to do with using strings to unify gravity and the standard model, which is what isn’t working at all.


    Yes, the way string theory is represented in the blogotub does a disservice to the field. There’s a well-known line from Yeats “The best lack all conviction, while the worst are full of passionate intensity”

    I think Siegel and Gates see themselves as somewhat out of the mainstream of string theory. Gates at UCF explicitly said they he was in a minority, and not just because of the color of his skin…


    No, I don’t agree with Gates about using that kind of metaphor. I think he sees himself as trying to be careful to distinguish speculation from solid science, but at the same time trying to transmit something about these ideas to a very large audience, including transmitting the enthusiasm of the scientists involved. This seems to me a very tricky business, all too easily giving people the impression that something that is very speculative and without experimental foundation is on a similar footing to something that we have a lot of evidence for.

  10. woit says:


    At some point I do hope to write more on these topics, although at the moment I’m much more trying to find time to push my own ideas about these things further along. To make clear exactly what I had in mind with those points, here’s a more specific version:

    1. We don’t understand non-perturbative gauge theories, especially ones with chiral fermion couplings very well at all. This is not just a mathematical problem, but a conceptual one, and new mathematical ideas might help.

    2. The representations of a gauge group in 1d are understood, this is the theory of loop group or affine Lie algebra representations. This theory allows us to understand certain 1+1d QFTs, especially WZW models. In higher dimensions, very little is known, probably including the fundamental question of what the right sort of representations is to look for.

    3. Absent experimental guidance, new ideas about unification may have to come from mathematics. Mathematics and physics seem to be connected in a very deep way, and understanding this connection may be our only way to make progress if we can’t probe higher energy scales experimentally.

  11. King Ray says:

    Peter, great talk at UCF, and it was a real pleasure to meet you in person! Thanks also for autographing my book.

  12. JJ says:

    Hi Peter:

    I would like to know if you have had the chance to read Tegmark´s last paper . It was discussed briefly at the N-Category Café . Although highly especulative I found it worth reading.

  13. Peter Woit says:


    I did take a look at the Tegmark paper you mention. Philosophically I think I’m somewhat in agreement with him about the “Mathematical Universe Hypothesis”, but to me it seems that to get anything out of it you need to understand what the fundamental mathematical structures out there are in a much more sophisticated way than he is doing.

  14. mclaren says:

    String theorists seem to be using the term “prediction” and “predictive” in a non-standard way. For example, Jacques Distler claims that “string theory is highly predictive” but when asked for published HEP journal articles making experimentally verified prediction, the string theorists refuse to provide any.

    Moreover, the 3 big results from experimental HEP-related physics of the last 20 years were not predicted by anyone. Not by the SM and not by string theorists: neutrino oscillation, dark matter, dark energy.

    Some will jump in to claim dark matter was predicted by the string theoretic superpartners but no one knows whether dark matter is due to superpartners. It could just as well be due to neutrino oscillation, or something else might be going on that we’re just not aware of yet. And no published HEP experiment has yet verified the existence of superpartners. In some cases, we haven’t even experimentally verified the existence of the original SM particle (graviton), let alone the superpartner (gravitino). So it sounds like that’s really putting the cart before the horse.

    So when people like Siegel say “This is also the only experimentally verified result of string theory,” it’s not clear what they mean. In the sense that string theory collapses down into all of current physics at low energies, string theory can be technically said to have lots of experimentally verified results… But they’re trivial results. The real test of a new theory isn’t whether it reproduces the results of a perfectly adequate existing theory like the Standard Model. It’s whether the new theory predicts phenomena which aren’t predicted by the old theory, and which are then confirmed by experiment.

    So far I’m not aware that string theory has done that.

  15. theoreticalminimum says:


    Maybe you should fix the following in your slides:

    pp 4, 5 : “different from”, not “different than”
    p 11 : -1 factor missing in Schrodinger equation.
    p 21 : At the time “it” was unclear…
    p 24 : As several generations of new accelerators have [been] come…
    p 24 : “… everything they have seen is compatible with the predictions of the SM” – Even neutrino masses? Dark matter?(?)
    p 29 : 1974 “Used” to quantize…
    p 31 : .. as to whether any “is” possible.

    Feel free to delete this comment after you’ve read it.

  16. Warren says:

    mclaren Said:

    So when people like Siegel say “This is also the only experimentally verified result of string theory,” it’s not clear what they mean…The real test of a new theory isn’t whether it reproduces the results of a perfectly adequate existing theory like the Standard Model. It’s whether the new theory predicts phenomena which aren’t predicted by the old theory, and which are then confirmed by experiment.

    Please see my previous sentence on that same webpage:

    “In fact, the only property of string theory not found in particle theory is Dolen-Horn-Schmid duality…”

    So far, no one has been able to derive DHS duality from any particle theory, the Standard Model in particular.

    Coin Said:

    What vaguely is this Doren-Horn-Schmid thing, if it’s not too much trouble to ask? Would you say that it qualifies as a “prediction” made by String Theory?

    In particle physics, you need to sum over exchanges of particles in both the s & t channels:

    Figure 1

    In string theory, you only have to sum over just s or just t, not both: The 2 sums are equal. That’s because either sum represents the exchange of a string worldsheet, which when stretched thin in one direction (s) or the other (t) looks like a particle worldline in that direction. Here’s a more complicated worldsheet for string scattering (I guess I need more figures on my webpages):

    Figure 2

    I guess you could call DHS duality more of a “postdiction”: The 1st string (then called “dual model”) amplitude was derived by requiring this property.

  17. Peter Woit says:


    Thanks for the editorial assistance. I fear that those slides ended up getting created under too much time pressure, so there’s a lot wrong with them, some of which you’re helping fix.

Comments are closed.