Is there a ‘smoking gun’ test for quantum gravity?

Quantum-entanglement experiments have been proposed to test whether gravity is quantum, but recent research suggests this might not be conclusive. Aziz and Howl report in Nature that entanglement can also occur in classical models of gravity, complicating efforts to definitively prove the quantum nature of gravity. Classical gravity, as per Einstein's general theory of relativity, describes gravitational interactions through smooth space-time deformations, whereas quantum gravity uses quantum rules involving gravitons. Despite earlier proposals suggesting that entanglement between masses could indicate a quantum link, Aziz and Howl's findings imply that such evidence may not be definitive proof of quantum gravity.

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