Classical Gravity Might Entangle Particles — New Study Maps How to Tell the Difference

For nearly a century physicists have tried to reconcile Albert Einstein’s General Theory of Relativity, which governs the very large, with quantum theory, which governs the very small. A new theoretical paper from researchers at the University of London shows that even if gravity itself remains classical, it could still induce quantum entanglement between particles — but with measurably weaker correlations than if gravity were fundamentally quantum.

The study, by Joseph Aziz and Richard Howl and published in the journal Nature, develops a mathematical framework describing how a classical gravitational interaction might produce observable quantum correlations. Rather than arguing that quantum gravity does not exist, the work maps specific differences in the strength and statistical character of entanglement that would allow experiments to discriminate between classical and quantum pictures of gravity.

How classical gravity could entangle

Usually, quantum entanglement is described as arising from exchanges of virtual quanta (for gravity, hypothetical virtual gravitons). Aziz and Howl instead show that classical gravitational fields can, in certain setups, mediate entanglement through indirect quantum processes involving matter. In those scenarios the gravitational field itself is not quantized, yet quantum correlations between particles can still emerge.

“You could think about the gravitational interaction as more general than just the mediation of the gravitational field,” Howl explained. “There could be quantum processes associated with it, and even if the gravitational field is classical the interaction could still potentially entangle matter.”

Distinctive experimental signatures

A key result of the paper is a clear, testable difference: if gravity is quantum, entangled particles should show stronger, more definitive correlations. If a classical gravitational interaction is producing the entanglement indirectly, the correlations will be weaker and obey different statistical bounds. That contrast provides a potential experimental signature to distinguish the two mechanisms.

However, the authors emphasize that designing such experiments is extremely challenging. Any test would need to exclude all competing sources of entanglement and suppress decoherence — the environmental processes that destroy fragile quantum superpositions. Despite these obstacles, the new theoretical bounds give experimentalists concrete targets and benchmarks as technology improves.

While the paper does not settle the question of whether gravity is ultimately quantum, it broadens the range of testable possibilities. By clarifying how a non-quantized gravitational interaction might still participate in quantum phenomena, Aziz and Howl’s work helps focus future experimental efforts aimed at probing one of physics’ deepest open questions.