Cosmology 2376.2 Discussion
E. Silverstein You have said that you think that dimensionality is conserved and
that the supercritical string theories do not mix with the rest. I do not under-
stand that comment because we know of such transitions.J. Polchinski I think they might mix in one direction, so if you go back in time
the dimension rises and you do not mix with the low-dimension stuff. That waswhat I was sort of hoping. I was hoping that there is some kind of scaling in
the large D limit.
J. Maldacena The supercritical strings have a tachyon, so this is not a well-defined
boundary condition in the future.E. Silverstein It is not true that every supercritical strings have a tachyon. Some
models do, and some models do not, just like with other string theories. It is
possible to project out tachyons in supercritical strings.A. Strominger A question to Polchinski: Why do you think it is possible to de-
cide how predictive science is? Are you asserting that, if you have an anthropic
explanation for something, it is possible to rule out that there is another expla-
nation that we have missed? Of course, if you were able to predict everything,
you would know that science was totally predictive. But if you fail to do that,
how can you even imagine ruling out some clever bleb field method of under-
standing things that we just had not thought about?J. Polchinski I think it is fair to say that we do not need to be skeptical until we
answer the question “what is string theory?”, a question which has a very long
future.A. Strominger What is string theory and whether string theory is related to our
world? Fair enough.J. Polchinski There is structure and correlations that you could not anticipate.
The cosmological constant is a smoking gun, there may be others. There is still
room for skepticism. It’s a Goedel thing. There are undecidable questions. We
should not assume a priori how predictive science is, it is not something we can
know.A. Strominger Right, but we can try as hard as we can to predict everything that
we are able to.J. Polchinski We can try relaxing different prejudices and see where each of them
leads.B. Greene Is it not important to draw a distinction between correlations and
explanations? I agree that one can find interesting correlations between various
features of the theory, but is that an explanation? No, it is just an interesting
correlation.J. Polchinski It is true, but it may be the way nature is. You cannot exclude that
this is the way nature is.