# Black Holes, Entanglement and Decoherence

## TL;DR

This paper reviews how black holes cause decoherence of nearby quantum superpositions through entanglement, radiation absorption, and interactions with fluctuating multipole moments, highlighting implications for quantum gravity horizons.

## Contribution

It presents three equivalent arguments explaining black hole-induced decoherence and discusses the connection between soft hair and internal degrees of freedom in quantum gravity.

## Key findings

- Black holes decohere quantum superpositions via entanglement.
- Absorption of soft radiation contributes to decoherence.
- Interactions with fluctuating multipole moments are significant.

## Abstract

It was recently shown that a black hole (or any Killing horizon) will decohere any quantum superposition in their vicinity. I review three distinct but equivalent arguments that illustrate how this phenomenon arises: (1) entanglement with "degrees of freedom" in the interior (2) the absorption of soft, entangling radiation emitted by the superposition and (3) interactions with the quantum, fluctuating multipole moments of a black hole arising from ultra low frequency Hawking quanta. The relationship between "soft hair" and interactions with "internal degrees of freedom" is emphasized and some implications for the nature of horizons in a quantum theory of gravity are discussed.