Matter-gravity entanglement entropy and the second law for black holes

TL;DR

The paper proposes that matter-gravity entanglement entropy can serve as an objective measure of entropy increase during black hole formation and evaporation, potentially resolving the black hole information paradox.

Contribution

It introduces matter-gravity entanglement entropy as a novel concept to explain entropy increase in black hole dynamics within a unitarily evolving framework.

Findings

Matter-gravity entanglement entropy may increase during black hole evaporation.

Photon-graviton interactions could contribute to entropy growth.

This approach offers a potential resolution to the black hole information paradox.

Abstract

Hawking showed that a black hole formed by collapse will emit radiation and eventually disappear. We address the challenge to define an objective notion of physical entropy which increases throughout this process in a way consistent with unitarity. We have suggested that (instead of coarse-grained entropy) physical entropy is matter-gravity entanglement entropy and that this may offer an explanation of entropy increase both for the black hole collapse and evaporation system and also for other closed unitarily evolving systems. For this to work, the matter-gravity entanglement entropy of the late-time state of black hole evaporation would have to be larger than the entropy of the freshly formed black hole. We argue that this may possibly be the case due to (usually neglected) photon-graviton interactions.