Talk by Professor Chethan Krishnan, CHEP, IISC Bengaluru at QASTM seminar
Channel: Sayantan Choudhury
Date: 2021-04-12

Title: Hints of Gravitational Ergodicity

Abstract: 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 paper, 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. This is a quantum chaotic system in which we expect to see
the Page curve in the full unitary description, while
semi-classically, eigenstates are expected to behave as though they
live in Berry's ensemble. We reproduce the unitarity-compatible Page
curve of this system, semi-classically. 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.

Speaker: Professor Chethan Krishnan, Center for High Energy Physics (CHEP) , Indian Institute of Science, Bengaluru, India.

Date and Time: 12th April, 2021, 6.30 PM to 9 PM India time (2:00 PM to 4:30 PM Berlin time).
Zoominar link: https://mpi-aei.zoom.us/j/97623339163

Contact: Dr. Sayantan Choudhury (sayantan.choudhury@niser.ac.in)