Decoherence of black hole superpositions

TL;DR

This paper investigates how Hawking radiation causes decoherence in a black hole superposition, revealing a simple, non-quantum-specific decoherence rate that contributes to the emergence of classicality.

Contribution

It introduces a novel analysis of black hole decoherence due to Hawking radiation, deriving a simple decoherence rate independent of Planck's constant.

Findings

Decoherence rate is given by a simple equation not involving 7h.

Black holes cannot be isolated from their Hawking radiation environment.

Decoherence explains the emergence of classical behavior from quantum superpositions.

Abstract

We consider the decoherence of a black hole "Schr\"odinger cat"- a non-local superposition of a Schwarzschild black hole in two distinct locations - due to the Hawking radiation it inevitably emits. An environment interacting with a system acquires information about its state, e.g. about its location. The resulting decoherence is thought to be responsible for the emergence of the classical realm of our Universe out of the quantum substrate. However, this view of the emergence of the classical is sometimes dismissed as a consequence of insufficient isolation and, hence, as non-fundamental (i.e., for practical purposes only). A black hole can never be isolated from its own Hawking radiation environment that carries information about its location. The resulting decoherence rate turns out to be given by a surprisingly simple equation that, remarkably (and in contrast to known cases of decoherence), does not involve Planck's constant $\hbar$.