Strongly incoherent gravity

TL;DR

This paper introduces a non-entangling, classical-like model of gravity that causes strong decoherence and can be tested through quantum coherence loss in small systems, challenging the quantum nature of gravity.

Contribution

It constructs a explicit non-entangling gravity model based on local measurements and feedback, demonstrating fundamental decoherence and loss of unitarity in gravitational interactions.

Findings

The model produces classical dynamics with no entanglement.

It contains parameters not yet excluded by observations.

Quantum coherence loss in atom interferometers can test the model.

Abstract

While most fundamental interactions in nature are known to be mediated by quantized fields, the possibility has been raised that gravity may behave differently. Making this concept precise enough to test requires consistent models. Here we construct an explicit example of a theory where a non-entangling version of an arbitrary two-body potential $V(r)$ arises from local measurements and feedback forces. While a variety of such theories exist, our construction causes particularly strong decoherence compared to more subtle approaches. Regardless, expectation values of observables obey the usual classical dynamics, while the interaction generates no entanglement. Applied to the Newtonian potential, this produces a non-relativistic model of gravity with fundamental loss of unitarity. The model contains a pair of free parameters, a substantial range of which is not excluded by observations to date. As an alternative to testing entanglement properties, we show that the entire remaining parameter space can be tested by looking for loss of quantum coherence in small systems like atom interferometers coupled to oscillating source masses.