4pm - 5pm
Tuesday 20 April 2021
Hints of gravitational ergodicity
Recent developments on black holes have shown that a unitarity-compatible Page curve can be obtained from an ensemble-averaged semi-classical approximation. In this talk, we emphasize (1) that this peculiar manifestation of unitarity is not specific to black holes, and (2) that it can emerge from a single realization of an underlying unitary theory. To make things explicit, we consider a hard sphere gas leaking slowly from a small box into a bigger box. We reproduce the unitarity-compatible Page curve of this system, semi-classically. Berry's ensemble in which the eigenstates live, plays a crucial role. The computation has structural parallels to replica wormholes, relies crucially on ensemble averaging at each epoch, and reveals the interplay between the multiple time-scales in the problem. Working with the ensemble averaged state rather than the entanglement entropy, we can also engineer an information "paradox". Our system provides a concrete example in which the ensemble underlying the semi-classical Page curve is an ergodic proxy for a time average, and not an explicit average over many theories. The questions we address here are logically independent of the existence of horizons, so we expect that semi-classical gravity should also be viewed in a similar light.
This event has passed
Visitor information
Find out how to get to the University, make your way around campus and see what you can do when you get here.