This week in Honolulu there’s a major particle physics conference going on, a joint meeting of the Division of Particles and Fields of the APS, and the Japanese Physical Society, called the Joint Meeting of Pacific Region Particle Physics Communities. Slides from the talks have started to appear here.
The conference is huge, with hundreds of talks (for some reason, attending a conference in Hawaii seems appealing to many people), and I haven’t had time to look at more than a few of them. Barry Barish gave a talk on international cooperation in HEP, Dave Schmitz one about the status of MiniBoone, which is “in the endgame” of a blind analysis of their neutrino experiment, with the black box containing their results to be opened in the not too distant future.
Lots of talks about string theory, including a plenary talk by Polchinski partly about AdS/CFT and attempts to use it to get information about QCD, partly about the landscape and string vacua. There was also a remarkable talk by Wati Taylor entitled Can String Theory Make Predictions for Particle Physics? Taylor begins by noting that “If we could do experiments at greater than 1019Gev, answer would probably be Yes”. “Probably” is different than the usual claims about this… His summary of the current state of string theory and particle physics goes like this:
- String theory need not make predictions for particle physics below 100 TeV
- We can’t define string theory yet
- The number of suspected solutions is enormous, and growing fast
- Nonetheless, constraints on low-energy physics correlated between calculable corners of the landscape may lead to predictions
- If not, probably need major conceptual breakthrough to have any possibility of predictivity for low-energy particle physics
- Raison d’etre for string theory: quantum gravity
I don’t know why he chose 100 TeV here, presumably just because it is probably an upper-bound on the likely energy scales particle physicists will be able to explore during the lifetimes of anyone now living. He could just as well have picked a much higher number. The only hope he sees for getting any kind of prediction using current versions of string theory is by finding correlations between things like numbers of generations and gauge groups when you examine large numbers of string vacua (this is similar to the conclusion reached by Michael Dine, described here). In work with Michael Douglas, he has found no evidence for this. Taylor also explains that the standard 10500 number often given for the number of string vacua seems to be a dramatic underestimate, and that it is even quite possible that the number is infinite when one takes into account non-geometric compactifications. Fundamentally, his conclusion seems to be that there is only a vanishingly small hope remaining of getting any predictions about particle physics out of string theory, so it has to be sold purely as a theory of quantum gravity, unless a miracle happens.
Taylor does make the case that string theory has found potential uses not in unification, but in studying strongly coupled gauge theory (AdS/CFT) and in suggesting new structures to try out in model-building. But at this point, he characterizes low energy physics predictions from string theory as unlikely, their appearance would just be an “unexpected bonus”. So, I guess the answer to the question of his title is basically “No”. Despite this, he does end by advertising the String Vacuum Project and listing the 17 prominent theorists who are asking the NSF to fund it.