Underground test of gravity-related wave function collapse

TL;DR

This paper reports an underground experiment testing the gravity-related wave function collapse proposed by Penrose, measuring faint radiation emission to set new bounds on the model's parameters, challenging its natural version.

Contribution

The study provides the first underground measurement of radiation emission from gravity-related wave function collapse, setting new bounds that challenge the natural Diosi-Penrose model.

Findings

Set a lower bound on the effective size of nuclear mass density.

Ruled out the natural parameter-free Diosi-Penrose model.

Detected faint radiation consistent with collapse predictions.

Abstract

Roger Penrose proposed that a spatial quantum superposition collapses as a back-reaction from spacetime, which is curved in different ways by each branch of the superposition. In this sense, one speaks of gravity-related wave function collapse. He also provided a heuristic formula to compute the decay time of the superposition $\mathord{-}$ similar to that suggested earlier by Lajos Di\'osi, hence the name Di\'osi-Penrose model. The collapse depends on the effective size of the mass density of particles in the superposition, and is random: this randomness shows up as a diffusion of the particles' motion, resulting, if charged, in the emission of radiation. Here, we compute the radiation emission rate, which is faint but detectable. We then report the results of a dedicated experiment at the Gran Sasso underground laboratory to measure this radiation emission rate. Our result sets a lower bound on the effective size of the mass density of nuclei, which is about three orders of magnitude larger than previous bounds. This rules out the natural parameter-free version of the Di\'osi-Penrose model.