Principle of Minimal Heating for Collapse and Hybrid Gravitational Models

Abstract

Energy nonconservation is a prominent, testable prediction of collapse and hybrid classical-quantum gravitational models. Without smearing of certain operators, the associated heating (or energy increase) rate diverges, yet the smearing distribution is arbitrary and, on scales much larger than the smearing length $r_C$, much of the phenomenology is expected to be independent of this choice. We propose to resolve this arbitrariness by a simple principle: for a fixed $r_C$, select the distribution that minimizes the heating rate. Conceptually, this should identify the minimal deviation from standard quantum mechanics and provide models that, once experimentally refuted, would strongly disfavor all variants with different distributions. We apply this approach to the most investigated collapse models: GRW, CSL, and DP. Notably, the Gaussian is optimal only for the GRW case. Finally, we apply it to the Tilloy-Diósi hybrid classical-quantum model of Newtonian gravity, leading to the minimally deviating variant of it. This version of the model is entirely determined by only one free parameter (the smearing length $r_C$) and, if experimentally refuted, would strongly disfavor any other version of it.