Entanglement as a source of black hole entropy

TL;DR

This paper reviews how quantum entanglement across a black hole horizon explains the proportionality of black hole entropy to the horizon area, emphasizing the role of different quantum states.

Contribution

It demonstrates that entanglement entropy accounts for black hole entropy in ground, coherent, and squeezed states, and explores the state-dependent scaling of entropy.

Findings

Entanglement entropy explains area-proportional black hole entropy in ground states.

The entropy scaling differs for excited states, less than proportional to area.

Identifies the degrees of freedom responsible for the entropy.

Abstract

We review aspects of black hole thermodynamics, and show how entanglement of a quantum field between the inside and outside of a horizon can account for the area-proportionality of black hole entropy, provided the field is in its ground state. We show that the result continues to hold for Coherent States and Squeezed States, while for Excited States, the entropy scales as a power of area less than unity. We also identify location of the degrees of freedom which give rise to the above entropy.