Can gravity account for the emergence of classicality?

TL;DR

This paper critically examines the claim that gravity-induced decoherence explains the quantum-to-classical transition, arguing that the evidence does not support gravity as the primary cause and emphasizing the importance of experimental context.

Contribution

The paper challenges previous claims that gravity causes universal decoherence leading to classicality, providing clarifications and disputing the universality of such effects.

Findings

Disputes the universality of gravity-induced decoherence

Highlights the importance of experimental context in observing interference

Argues gravity is not responsible for the quantum-to-classical transition in discussed scenarios

Abstract

A recent debate has ensued over the claim by Pikovski et al. [Nat. Phys. 11, 668 (2015)] that systems with internal degrees of freedom undergo a universal, gravity-induced, type of decoherence that explains their quantum-to-classical transition. This decoherence is supposed to arise from the different gravitational redshifts experienced by such systems when placed in a superposition of two wave packets at different heights in a gravitational field. Here we investigate some aspects of the discussion with the aid of simple examples. In particular, we first resolve an apparent conflict between the reported results and the equivalence principle by noting that the static and free-fall descriptions focus on states associated with different hypersurfaces. Next, we emphasize that predictions regarding the observability of interference become relevant only in the context of concrete experimental settings. As a result, we caution against hasty claims of universal validity. Finally, we dispute the claim that, at least in the scenarios discussed by Pikovski et al., gravitation is responsible for the reported results, and we question the alleged ability of decoherence to explain the quantum-to-classical transition. In consequence, we argue against the extraordinary assertion by Pikovski et al. that gravity can account for the emergence of classicality.