A brief history of Hawking's information paradox

¹ Department of Physics and Astronomy, University of Sussex - Brighton, BN1 9QH, UK
² Department of Physics and Astronomy, Michigan State University - East Lansing, MI 48823, USA

^(a) x.calmet@sussex.ac.uk (corresponding author)
^(b) hsusteve@gmail.com

Received: 19 April 2022
Accepted: 18 July 2022

Abstract

In this invited review, we describe Hawking's information paradox and a recently proposed resolution of it. Explicit calculations demonstrate the existence of quantum hair on black holes, meaning that the quantum state of the external graviton field depends on the internal state of the black hole. Simple quantum mechanics then implies that Hawking radiation amplitudes depend on the internal state, resulting in a pure final radiation state that preserves unitarity and, importantly, violates a factorization assumption which is central to the original paradox. Black hole information is encoded in entangled macroscopic superposition states of the radiation.