Test of gravity-related collapse in the Diosi-Penrose model
In plain words
Penrose proposed that a mass in a superposition of two places decays in a time of about $\hbar$ divided by the gravitational energy of the difference between the two mass arrangements. Detecting or excluding this needs massive superpositions or very quiet detectors.
Precise statement
In the Diosi-Penrose model a superposition decays at rate $\Gamma = E_G / \hbar$, with $E_G$ the gravitational self-energy of the difference of the two mass distributions, regularized by a length $R_0$. X-ray bounds give $R_0 > 4.9e-8\,\mathrm{cm}$ (XENONnT, 90 percent C.L.) for the Markovian version. Determine whether a superposition experiment, or a non-radiating dissipative version of the model, can reach the regime where $\Gamma$ exceeds all environmental decoherence for allowed $R_0$, and measure or exclude it.
What would settle it
Observation or exclusion of excess decoherence at rate $E_{G} / \hbar$ in a massive superposition where environmental rates are below it.
Status in the literature
Unverified note
Underground X-ray searches (Donadi et al., Nature Physics 2021; XENONnT, Phys. Rev. Lett. 136, 120201, 2026) excluded the Markovian model with $R_0$ below about $5e-8\,\mathrm{cm}$, about fivefold beyond the previous Majorana Demonstrator bound; larger $R_0$ and dissipative versions are untested.