Schr\"odinger's Black Hole Cat

TL;DR

This paper introduces a novel framework combining quantum superposition and spacetime to study quantum-gravitational effects, enabling calculations of physical observables in superposed spacetime scenarios.

Contribution

It proposes a bottom-up approach to model genuine superpositions of spacetimes using quantum field theory in curved space, advancing the understanding of quantum gravity.

Findings

Calculated transition probabilities in superposed de Sitter spacetime.

Analyzed effects of spacetime superpositions on quantum matter.

Demonstrated a method to describe genuine superpositions of spacetimes.

Abstract

In the absence of a fully-fledged theory of quantum gravity, we propose a "bottom-up" framework for exploring quantum-gravitational physics by pairing two of the most fundamental concepts of quantum theory and general relativity, namely quantum superposition and spacetime. We show how to describe such "spacetime superpositions" and explore effects they induce upon quantum matter. Our approach capitalizes on standard tools of quantum field theory in curved space, and allows us to calculate physical observables like transition probabilities for a particle detector residing in curvature-superposed de Sitter spacetime, or outside a mass-superposed black hole. Crucially, such scenarios represent genuine quantum superpositions of spacetimes, in contrast with superpositions of metrics which only differ by a coordinate transformation and thus are not different according to general relativity.