Despite decades of effort, a theory of quantum gravity is still out of grasp. Now a group of physicists have proposed an experimental test of whether gravity is quantum or not, to settle questions about the force’s true nature.
The search for quantum gravity is an effort to reconcile Einstein’s general relativity with quantum mechanics, which is a theory of all the fundamental particles and the forces that act on them – except gravity. Both are needed to explain what happens inside black holes and what happened at the big bang. But the two theories are incompatible, leading to apparent paradoxes and things like singularities, where the theories break down.
If gravity is a quantum mechanical force, adjacent free-falling masses, each of which is in a superposition of being in two places at once, could get entangled by gravity such that measuring the properties of one mass could instantly influence the other. To test this, Sougato Bose of University College London and his colleagues have proposed an experiment.
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