One of the challenges of distinguishing between classical and quantum theories of gravity is how to distinguish the two experimentally. A new paper make a precise generic prediction about quantum gravity theories that could do just that.
Specifically, gravitational interactions that are present in quantum gravity, but not in classical gravity should trigger a transition from "coherent" to "decoherent" behavior in light and massive particles propagating through space at a precisely quantifiable distance that is a function of particle velocity for massive particles and a function of frequency for photons.
These are measurable properties of particles (at least statistically) and the distances involved reasonably susceptible to measurement.
The paper is as follows: