Replica Wormholes and Quantum Hair

Abstract The recent applications of Euclidean path integrals to the black hole information problem are discussed. In calculations with replica wormholes as the next‐to‐leading order correction to the Gibbons–Hawking saddlepoint, the radiation density matrix approaches a pure state at late times, following the Page curve. The unitary evaporation of black holes (in real time), mediated by calculable quantum hair effects, are compared with the replica wormhole results. Both the replica wormhole and quantum hair approaches imply that radiation states are macroscopic superpositions of spacetime backgrounds, invalidating firewall and monogamy of entanglement constructions. Importantly, identification of modes inside the horizon with radiation modes (i.e., large‐scale nonlocality across the horizon) is not required to provide a physical picture of unitary evaporation. Radiation modes can encode the interior information while still remaining independent degrees of freedom.