High Energy Theory Seminar
Hawking famously observed that the formation and evaporation of black holes appears to violate the unitary evolution of quantum mechanics. Nonetheless, it has been recently discovered that a signature of unitarity, namely the "Page curve" describing the evolution of entropy, can be recovered from semiclassical gravity. This calculation involves `spacetime wormholes' in the gravitational path integral, which connect distant regions of spacetime with an amplitude independent of their separation. I will discuss the close connection between these ideas and the physics of closed "baby" universes, concentrating on asymptotically AdS boundary conditions, where they are associated with an ensemble of dual CFTs. From this perspective, we can understand the Page curve as a surprising and novel nonperturbative consequence of diffeomorphism invariance.