On the other coast, today and tomorrow at Princeton there will be a workshop on string cosmology and inflation. They have a list of questions to be addressed, including
Are there any plausible alternatives to string/M-theory as a fundamental theory of physics?
Does string theory make any cosmological predictions? Does it exclude anything?
As far as I can tell, there’s an odd consensus set of answers to these two questions among string theorists. No, string theory makes no predictions about cosmology, but also no, there are no alternatives.
For an interesting discussion of the problems raised by this sort of “no possible predictions, but no alternatives” situation, see this debate involving John Horgan, David Tong and Tara Shears. Horgan does a good job of pointing out the problem. Tong’s defense of string theory relies heavily on claiming that it is highly mathematically rigid, so mathematical consistency is what can give us faith in it. One problem with this is that the whole string theory landscape picture is an extremely ill-defined conjectural framework, the opposite of mathematically rigid. Yes, there are parts of string theory that seem to be mathematically consistent and lead to interesting results. The problem is that those have nothing to do with what is observed about fundamental physics.
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