High Energy Theory Seminars

Title: Quantum Mechanics and Observers for Gravity in a Closed Universe

Abstract: In recent years we have seen substantial progress on the quantum theory of black holes using semiclassical methods such as the quantum extremal surface formula and the path integral. Applying these same methods to quantum cosmology however leads to a rather crazy conclusion: the Hilbert space of quantum gravity in a closed universe is one-dimensional and real. Is this really true? How can it possibly be consistent with the richness of human experience? In this talk I will review the arguments leading to a one-dimensional Hilbert space, and then describe a recent proposal for how they might be compatible with reasonable semiclassical physics.