What is "quantum" about quantum gravity?

TL;DR

This paper explores how the equivalence principle influences interpretations of quantum mechanics in the context of quantum gravity, suggesting relational interpretations are more compatible with a covariant quantum dynamics.

Contribution

It argues that the equivalence principle favors epistemic over ontic interpretations of quantum mechanics and proposes modifications to relational interpretations to incorporate gravity.

Findings

Relational interpretations can accommodate the equivalence principle.

Assumption of classical-quantum separation must be relaxed in quantum gravity.

Speculation on a covariant quantum dynamics compatible with gravity.

Abstract

Assuming the validity of the equivalence principle in the quantum regime, we argue that one of the assumptions of the usual definition of quantum mechanics, namely separation between the ``classical'' detector and the ``quantum'' system, must be relaxed. We argue, therefore, that if both the equivalence principle and quantum mechanics continue to survive experimental tests, that this favors ``epistemic'' interpretations of quantum mechanics (where formalism is built around relations between observables) over ``ontic ones'' (assuming the reality of states and wavefunctions). In particular, we show that relational type interpretations can readily accomodate the equivalence principle via a minor modification of the assumptions used to justify the formalism. We qualitatively speculate what a full generally covariant quantum dynamics could look like, and comment on experimental investigations.