Unitarity and the information problem in an explicit model of black hole evaporation

TL;DR

This paper examines the black hole information paradox using an explicit evaporation model, questioning assumptions about unitarity and horizons, and suggesting that unitarity may not be preserved in semiclassical descriptions.

Contribution

It provides a detailed analysis of unitarity in black hole evaporation within an explicit spacetime model, challenging common semiclassical interpretations.

Findings

Semiclassical unitarity statements may be violated even if physics is fundamentally unitary.

No horizon firewall is necessary under the proposed model.

Results are compatible with recent holographic studies.

Abstract

We consider the black hole information problem in an explicitly defined spacetime modelling black hole evaporation. Using this context we review basic aspects of the problem, with a particular effort to be unambiguous about subtle topics, for instance precisely what is meant by entropy in various circumstances. We then focus on questions of unitarity, and argue that commonly invoked semiclassical statements of long term, evaporation time, and Page time "unitarity" may all be violated even if physics is fundamentally unitary. This suggests that there is no horizon firewall. We discuss how the picture is modified for regular (nonsingular) evaporation models. We also compare our conclusions to recent holographic studies, and argue that they are mutually compatible.