Black Hole Information Revisited

TL;DR

The paper argues that four-dimensional black hole evaporation cannot be fully thermal once soft gravitons are included, and that unitarity may be restored through correlations between hard Hawking quanta and soft gravitational dressings. It adopts a Faddeev-Kulish dressing framework and a hard-soft factorization, proposing an orthogonality relation between soft clouds associated with different hard emission histories. In a restricted graviton-only model, the soft sector can encode the information needed to purify the hard Hawking radiation, while a detector observing only hard quanta sees the Hawking spectrum. The work outlines a soft hair mechanism for information retention, though generalization to realistic multi-particle spectra and full state reconstruction remains an open research direction.

Abstract

We argue that four-dimensional black hole evaporation inevitably produces an infinite number of soft particles in addition to the thermally distributed `hard' Hawking quanta, and moreover that the soft and hard particles are highly correlated. This raises the possibility that quantum purity is restored by correlations between the hard and soft radiation, while inclusive measurements which omit the soft radiation observe the thermal Hawking spectrum. In theories whose only stable particle is the graviton, conservation laws are used to argue that such correlations are in principle sufficient for the soft gravitons to purify the hard thermal ones.