Classical Wormholes,Quenched Free Energy, and the Gravitational Replica Trick

Recent developments have revealed that at least in certain contexts, the gravitational path integral predicts unitary evolution of black hole evaporation as long as Euclidean wormholes are included. The inclusion of such wormholes suggests an interpretation of the path integral as some kind of ensemble average. In this talk, I'll discuss how the presence of these wormholes can make a contribution to the gravitational free energy, which can be computed from the path integral via a replica trick distinct from the more familiar one used to compute von Neumann entropies. I'll sketch how this replica trick works using a two-dimensional model of dilaton gravity -- JT gravity -- as a prototypical example. In pure JT gravity, the contributions of replica wormholes only affect the free energy at nonperturbatively small temperature. In the case of JT coupled to matter, however, the replica wormholes can be stabilized even in a classical approximation; I'll report progress on understanding the contribution of these wormholes to the the gravitational generating functional in a classical limit.