Microscopic Origin of Page Curve

Abstract

Applications of the Ryu-Takayanagi formula to evaporating black holes are known to reproduce the Page curve, although leaving open the microscopic origin of the necessary black hole degrees of freedom responsible for the entanglement and microstates. Here, we fill this gap by utilizing a recently proven generalized Ryu-Takayanagi formula which keeps the contact to the theory's Hamiltonian phase space. Precisely, we show that in any diffeomorphism invariant field theory containing stationary black holes with bifurcate Killing horizons the phase space states distinguishable by their Hamiltonian surface charges over the bifurcation surface must provide the degrees of freedom responsible for the black hole's Wald entropy. This result is part of a larger program where measurable quantities of a quantum theory are expressed as weighted sums over paths in the theory's phase space. Suited reorganization tools for those sums make then physical phenomena evident which might be obscured in a naive summation relying on spacetime notions such as field configuration spaces and Feynman diagrams. Besides presenting this result, we provide here a conceptual overview of the program as an entry point for unfamiliar readers explaining the central notion of the program and why it reveals the results obtained so far. These include especially the gravitational entropy bound and the here applied generalized Ryu-Takayanagi prescription shown earlier within the program. Using the information paradox as a leitmotif, our proposed program uncovers black hole hair that may be hidden within a naive spacetime interpretation.