Predictions of theories that combine quantum mechanics with gravity could be observed using highly sensitive photon detection in a tabletop experiment.
Quantum-gravity theories attempt to unite gravity and quantum mechanics. A proposed tabletop experiment called Gravity from the Quantum Entanglement of Space Time (GQuEST) would search for a predicted effect of such theories using a new type of interferometer—one that counts photons rather than measuring interference patterns. The GQuEST team has now calculated the sensitivity of their design and shown that it can recover the predicted signal 100 times faster than traditional interferometer setups [1].
Quantizing gravity implies that spacetime is not continuous—it becomes “pixelated” when you look at scales as small as 10−35 m, far too small to be probed in any experiment. However, certain quantum-gravity models predict that spacetime can fluctuate—a kind of spontaneous stretching and squeezing in the spacetime fabric that might produce observable effects [2]. “You couldn’t detect a single pixel, but you could detect the coherent fluctuations of many pixels,” says Caltech theorist Kathryn Zurek. She has formulated a “pixellon” model, which predicts that collective fluctuations inside an interferometer can cause a detectable frequency change, or modulation, in the interferometer’s output light [3].
