The Page curve and baby universes

Abstract

Black hole thermodynamics suggests that, in order to describe the physics of distant observers, one may model a black hole as a standard quantum system with density of states set by the Bekenstein-Hawking entropy $S_{\mathrm{BH}}$. This idea has long been considered to be in strong tension with Hawking's prediction that radiation from black holes is nearly thermal, and with low-energy gravity more generally. But the past two years have shown that low-energy gravity does offer a self-consistent description of black hole evaporation consistent with the above idea, and which in particular reproduces the famous Page curve. We provide a brief overview of this new paradigm, focusing on Lorentz-signature asymptotically-flat spacetimes, and emphasising operationally-defined observables that probe the entropy of Hawking radiation.

8 pages. Selected for Honorable Mention in the 2021 Gravity Research Foundation Essays Competition

References in corpus (2)

• Black holes as mirrors: quantum information in random subsystems
• Deriving covariant holographic entanglement

Cited by in corpus (11)

• Spacetime foam: a review
• Page Curve for Entanglement Negativity through Geometric Evaporation
• Planar Black Holes in Holographic Axion Gravity: Islands, Page Times, and Scrambling Times
• Page Curve of Effective Hawking Radiation
• Complex Saddles and Euclidean Wormholes in the Lorentzian Path Integral
• Defect extremal surfaces for entanglement negativity
• Microstructure in matrix elements
• Reflected Entropy and Entanglement Negativity for Holographic Moving Mirrors
• A "black hole theorem," and its implications
• The black hole information puzzle and the quantum de Finetti theorem
• Gravitational thermodynamics without the conformal factor problem: Partition functions and Euclidean saddles from Lorentzian Path Integrals