Breakdown of locality in quantum gravity

In recent years, we've gained increasing evidence that some degree of nonlocality will be fundamental to the eventual theory of quantum gravity. The objective of this thesis is to investigate various aspects of this idea as manifested in two interrelated areas, namely black hole thermodynamics and the holographic principle. Specifically, in the former, we consider the black hole information or firewall paradox, and show that the constraints of causality may prevent an observer from identifying a conflict. We then turn to holography in the form of the AdS/CFT correspondence, with the aim of clarifying how information about the bulk spacetime is encoded in the boundary field theory. We uncover an obstacle to current prescriptions for reconstructing non-trivial spacetimes from CFT data. We also introduce a toy model that allows one to explicitly localize information on the boundary, using either gauge freedom or ideas from quantum error correction. We compute the spectrum of CFT operators for this simple model, and use it to examine the set of possible criteria a generic CFT must satisfy in order to have a well-defined bulk dual.