Taylor’s talk was quite remarkable, very explicitly going over exactly how bad the current situation is for efforts to get any prediction at all out of string theory. There was a lot of discussion with the audience, and much nervous laughter. Unfortunately I found some of Gross’s comments hard to hear. Taylor explained that after spending ten years himself working on trying to better understand what string theory is (he worked in string field theory), he doesn’t see any realistic prospects for significant progress on this problem during the next ten years. He listed the basic problems as the lack of a non-perturbative definition in anything but special, non-physical backgrounds, the inability to do even perturbative calculations in the kind of Ramond-Ramond backgrounds that people are using to stabilize moduli, and the lack of any definition of string theory when supersymmetry is broken by a positive CC, and thus the background is deSitter.
Discussing the landscape, he said that there was no evidence for a dynamical principle that would select the vacuum, with no hint at all of how such a thing would work, and that there is no known mechanism that would destabilize the known conjectured constructions of vacua. He goes on to ask “what can we do even if we don’t know what we’re talking about?”