A test for distinguishing between the quantum and relativistic interpretations of time is proposed in Nature Communications this week. This could pave the way to measuring how quantum effects alter the general relativistic notion of time.

According to general relativity, time flows at different rates depending on the geometry of space-time. While this has been precisely verified by experiments, it has never been tested when quantum effects are relevant. Magdalena Zych and colleagues devise such a test for a particle with an evolving internal degree of freedom — in effect a quantum clock — and predict that its behaviour in a gravitational potential can only be explained using the general relativistic notion of time.

Because quantum mechanics and general relativity are based on different premises, this proposal could have far-reaching implications for physicists’ understanding of their interplay.