Strings 2007 is starting today, and already there seem to be a large number of different laptops connecting to this blog from wlan.uam.es. I’m hoping that some of their owners will write in here with news of how the conference is going. I’ll also try and add links here to any blog and press coverage of the conference that I see or hear about.
Witten’s new 83 page paper entitled Three-Dimensional Gravity Revisited appeared on the arXiv last night and presumably this is the detailed version of what he’ll be talking about in the first of tomorrow’s talks at the conference. It corresponds pretty much to what he talked about here in New York a few weeks ago, which was described here. I assume many of those laptops at the conference are being used to download and read copies of Witten’s paper. At his blog, Clifford Johnson notes that he won’t be at Strings 2007, and hopes that this will ensure that there will be an exciting breakthrough announced there, just like what happened when he decided not to attend Strings 1995.
As I write this, I see that string theorist Jacques Distler is there live-blogging. Here’s the first of his reports.
Update: Some of the slides of the talks are already on-line. The slides for Witten’s talk are available here.
Update: There’s an interesting posting here by Jacques Distler about the Witten talk, and, for those who enjoy such things, quite a rant from Lubos here, prompted by my comment that in this case Witten is investigating quantum gravity using non-perturbative QFT, not strings.
I’ve been reading Witten’s paper a bit more carefully, and it raises all sorts of interesting issues. He makes the point that even in 3d, we really don’t know exactly what “non-perturbative pure quantum gravity” is. He uses the Chern-Simons formulation of 3d gravity in terms of gauge theory to motivate his guess at the correct boundary CFT, and then once he has that he has something much more well-defined to study.
This is a bit reminiscent of the compact, non-gravitational situation. There Chern-Simons theory works fine perturbatively, but to understand the non-perturbative theory one connects it to a CFT on the boundary, in this case the Wess-Zumino model (this is the story that got Witten a Fields medal).
Update: B. Yen has set up a video-blog for Strings 2007, where there will be iTunes podcasts of the conference available.
Update: Latest report from Jacques Distler is that, since Witten’s one, which he got to write about:
there have been some very cool talks
(emphasis in the original), but he can’t tell us even which ones they were since his laptop is malfunctioning. Slides of the talks are available here. I’ve looked through them and, besides Witten’s, don’t see anything I would describe as “very cool”, but maybe that’s just me.
Update: All the talks are on-line now and I just looked through the last of them, and watched the summary talk by Gross. Lisa Randall discussed recent calculations of black-hole production at colliders, with the bottom line being that even in the unlikely event the gravity scale is within reach of the LHC, existing bounds already pretty much rule out the possibility of seeing the kind of dramatic effects from black hole production that have been widely advertised as something that might be seen at the LHC.
Gross noted that the conference was much less mathematical than last year’s, possibly because Yau was not involved in organizing it. He was most enthusiastic about describing the many talks on AdS/CFT, especially the Beisert talk which told about recent progress in getting an exact solution of N-4 SYM. Some talks referred to possible applications of AdS/CFT not just in QCD and heavy-ion physics, but in condensed matter physics (using the duality to get info about relevant CFTs). He told about Polchinski’s speculation that “maybe AdS/CFT will solve high Tc superconductivity”, but dismissed it with “sounds great, but seems unlikely to me.” He dealt with the landscape talks by flashing them by quickly, in a lower and less enthusiastic voice, noting that they made up at least a quarter of the talks at the conference. He dealt similarly with the cosmology/anthropic talks, describing Bousso’s as “an attempt to make the anthropic principle precise if not respectable.”
After the summary, he gave his own take on the state of string theory, saying that one had to be honest about the lack of falsifiable predictions and that now he had a slide headed “The Failures of String Theory”. He continues to feel that the main failure is because we “don’t know what string theory is”, that something is missing, some principle that would pick out not a “vacuum” but a “cosmology”, one perhaps using new ideas about what space and time are. He said he was not too upset by the landscape, because “we don’t know what the rules are” in string theory, so one can’t argue that string theory implies the landscape. He appeared to feel that he is losing the debate, complaining that this used to also be the opinion of his colleagues, but that they were going over to the other side because of the cosmological constant, saying that if another explanation of the CC was found 90% of the anthropicists would come back to his side. He tried to minimize the size of the CC problem, measuring it with respect to a supposed 1 TeV SSYM breaking scale and working in energy, not energy density units, so it is only too small by a factor 1016. He compared this to Dirac’s famous large number problem (which Dirac tried to solve not anthropically, but by time-varying constants, leading to a prediction that was falsified), which was finally “explained” by asymptotic freedom. His message to the anthropocists was “just because you don’t know an explanation doesn’t mean it doesn’t exist”.
Finally he mentioned that Strings 08 will be at CERN, Strings 09 in Rome, and no one has yet agreed to host Strings 10. He argued that the series of Strings conferences “must go on”, because they are “like the canary in the coal mine”, and if they stop that would be a very bad sign for string theory.
I’m curious to know what those in attendance thought of this; it wasn’t exactly a rousingly optimistic portrayal of the state of the subject…
Update: There’s an article in El Pais about the conference and about the state of string theory. My Spanish isn’t perfect, but as far as I can tell the piece was pretty much pure unadulterated hype, of the sort that it is one goal of the Strings XX bashes to generate.
Update: Jacques Distler finally got his computer fixed, and posted about one example of what he considered a “very cool talk” with exciting new ideas. Unfortunately, it seems the ideas are not that new, since a commenter wrote in to his blog to point to papers from four and a half years ago that do pretty much the same thing.