Evaporating Firewalls

TL;DR

This paper explores how entanglement with an auxiliary system can lead to the evaporation of firewalls in AdS black holes, potentially restoring smooth horizons in the dual gravity description.

Contribution

It demonstrates a specific scenario where an evaporating black hole's firewall can disappear through entanglement with a second CFT, linking firewall evaporation to the thermofield double state.

Findings

Firewall can evaporate when the system evolves to the thermofield double state.

Entanglement with an auxiliary CFT can enable smooth horizons in black hole evaporation.

The nature of the horizon depends on the initial state and entanglement structure.

Abstract

In this note, we begin by reviewing an argument (independent from 1304.6483) that the large AdS black holes dual to typical high-energy pure states of a single holographic CFT must have some structure at the horizon (i.e. a firewall/fuzzball). By weakly coupling the CFT to an auxiliary system, such a black hole can be made to evaporate. In a case where the auxiliary system is a second identical CFT, it is possible (for specific initial states) that the system evolves to precisely the thermofield double state as the original black hole evaporates. In this case, the dual geometry should include the "late-time" part of the eternal AdS black hole spacetime which includes smooth spacetime behind the horizon of the original black hole. Thus, we can say that the firewall evaporates. This provides a specific realization of the recent ideas of Maldacena and Susskind that the existence of smooth spacetime behind the horizon of an evaporating black hole can be enabled by maximal entanglement with a Hawking radiation system (in our case the second CFT) rather than prevented by it. For initial states which are not finely-tuned to produce the thermofield double state, the question of whether a late-time infalling observer experiences a firewall translates to a question about the gravity dual of a typical high-energy state of a two-CFT system.