Emergent Spacetime 211role in anything that we’re talking about? Could we see that if we spoke notjust about emerging z and t, but emerging topological/differential structure,
we’d see that maybe the exotic structures are there in some meaningful way
and they need to be taken account of. And then one can talk about emerging
geometrical structure on top of those. I do not know if that is a worthwhileframework to think about it, but it would help sharpen, I think, what we mean
by emerging spacetime.J. Harvey Well, it is certainly an interesting question whether things can emerge
that we don’t think describe reality and why they do not emerge.
T. Banks I want to emphasize a point that was made both by Juan and Nati
about the question of trying to understand what we need to do to have a
macroscopic spacetime, a spacetime with low curvature that’s well-described
by gravity. And I would claim that in the well-understood examples beyond
1 + 1 dimensions, we always need to have supersymmetry that’s either exact
or restored asymptotically in the low-curvature region. The landscape proposal
gives examples which claim that this is not a...J. Harvey In order to have moduli spaces, you mean?
T. Banks No, well, in the BFSS matrix model, in order to have moduli spaces
so that you can talk about large distance scattering, you need to have exact
supersymmetry. In AdS/CFT, in all the examples that we really understand,
in order to have a low-curvature Ads space, in the sense that Juan discussed,
we have to have exact supersymmetry. There are claims in the literature about
examples where that’s not true, I think it’s extremely important for us to try
to find the conformal field theories that supposedly describe completely non-
supersymmetric, very low curvature Ads space.
J. Harvey That is a good point.
S. Weinberg I would like to offer a remark that is so reactionary that 1 might be
J. Harvey It is almost time for lunch, so do not worry.
S. Weinberg Listening to the discussion this morning, which I found very stimu-
lating, I was nevertheless reminded of the kind of discussion that went on in the
late 1930’s and early 1940’s about the problems of fundamental physics. There
were internal problems of not knowing how to do calculations, and external
problems of anomalies in cosmic rays, because although they didn’t know it,
they were confusing pions and muons, and most people at that time thought
that fundamental new ideas were needed, that we had to go beyond quantumfield theory as it had been constructed by Heisenberg and Pauli and others, and
have something entirely new, something perhaps non-local, or a fundamental
length. It turned out that the solution was to stick to quantum field theory, and
that it worked. It occasionally occurs to me, well, maybe that is the solution
now, that there is not an emergent space-time, that we just have three space
and one time dimension, and that the solution is quantum field theory. Nowejected from the room.