When does entanglement through gravity imply gravitons?

TL;DR

This paper critically examines claims linking gravitationally mediated entanglement to the existence of gravitons, clarifying causality notions and the role of quantum fluctuations.

Contribution

It clarifies the conditions under which entanglement through gravity implies gravitons, emphasizing the importance of retardation effects and causality distinctions.

Findings

Neglecting quantum fluctuations affects complementarity and no-signalling violations depending on the approximation.

Entanglement is generated locally in spacetime regardless of fluctuation considerations.

Detection of retardation effects in gravitational entanglement supports the existence of gravitons.

Abstract

Detection of entanglement through the Newtonian potential has been claimed to support the existence of gravitons, by extrapolating to a thought experiment which demonstrates that complementarity and causality would be in conflict unless quantum fluctuations exist. We critically assess this consistency argument using scalar field models. We show that whether complementarity or no-signalling is violated when quantum fluctuations are neglected, depends on how this approximation is taken, while in both cases entanglement is generated locally in spacetime. We clarify that the correct reading of the paradox requires making a clear distinction between two notions of causality violation: Newtonian action-at-a-distance and the quantum mechanical no-signalling; the latter is pertinent while the former is not. We conclude that the thought experiment (a) does not add to the epistemological relevance of entanglement through Newtonian potentials (b) lends support for the existence of gravitons, if retardation effects are detected in entanglement through gravity.