Apocalyptic quantum gravity

Black holes are regions of spacetime from which nothing can escape. This is already strange, but more puzzling is the fact that, over time, quantum mechanics causes black holes to leak energy and disappear. What happens to the objects that fell inside? The unitarity of quantum mechanics suggests one answer, and computations in semiclassical gravity another. To determine which is correct, we need to understand how quantum and gravitational effects interact.

This thesis develops techniques to peer inside black holes and track the flow of information. We exploit and extend the AdS/CFT correspondence, an approach to quantum gravity in which data at the boundary of spacetime is related to geometric structure in the bulk. The basic strategy is to make highly symmetric incisions along the boundary, dual to surfaces in the bulk called end-of-the-world (ETW) branes, since they literally terminate spacetime. In some cases, these branes can reach inside the black hole interior and teach us about what happens there. We also carefully study the quantum mechanics of ETW branes and find that the scalpels needed to make the incisions are finely tuned, hidden like the needle in a proverbial haystack of consistent microscopic boundary conditions.