Comment on "The black hole final state"

TL;DR

This paper critiques the final-state boundary condition proposal for black hole unitarity, highlighting how internal interactions could lead to information loss during black hole evaporation.

Contribution

It identifies potential departures from unitarity in the black hole final-state scenario due to internal interactions, challenging previous assumptions.

Findings

Interactions inside the horizon can cause non-unitary evolution.

Information loss depends on the entanglement of internal interactions.

Final-state boundary conditions may not fully preserve unitarity.

Abstract

Horowitz and Maldacena have suggested that the unitarity of the black hole S-matrix can be reconciled with Hawking's semiclassical arguments if a final-state boundary condition is imposed at the spacelike singularity inside the black hole. We point out that, in this scenario, departures from unitarity can arise due to interactions between the collapsing body and the infalling Hawking radiation inside the event horizon. The amount of information lost when a black hole evaporates depends on the extent to which these interactions are entangling.