Black Holes, Cavities and Blinking Islands

TL;DR

This paper studies how placing a black hole in a cavity affects entanglement entropy and islands, revealing a universal 'blinking island' phenomenon that influences information paradox considerations.

Contribution

It introduces the concept of blinking islands caused by cavity boundaries, providing new insights into entanglement dynamics and the black hole information paradox.

Findings

Entanglement entropy saturates below thermodynamic entropy.

Boundary conditions induce a universal blinking island effect.

Short-time information paradox arises from island disappearance.

Abstract

Placing a black hole in a cavity provides a natural framework for exploring gravitational scales, thermodynamic instabilities, and effective gravity theories. In this paper, we examine the evolution of entanglement entropy and entanglement islands in a two-sided extension of the Schwarzschild black hole in a cavity. By introducing a reflecting boundary in the eternal black hole exteriors, we regulate the infrared modes of Hawking radiation, finding that the entanglement entropy eventually saturates at a constant value. This value can be lower than the black hole thermodynamic entropy, thus avoiding the Page formulation of the information paradox. Regarding entanglement islands, we identify a universal effect induced by the boundary, which we term the ``blinking island'' -- where the entanglement island temporarily disappears, resulting in a short-time information paradox.