Here’s a mind-bending idea: What if gravity, the force we’ve long considered classical, could actually entangle matter at the quantum level? This is the bold claim of a new study by Joseph Aziz and Richard Howl from Royal Holloway University of London, published in Nature. Their research challenges the widely held belief that gravity must be quantized to mediate quantum entanglement—a phenomenon where particles remain connected even when separated by vast distances. But here’s where it gets controversial: Aziz and Howl argue that even a classical gravitational field could, in principle, entangle matter, upending decades of assumptions in the quest to unify quantum mechanics and Einstein’s general relativity.
The struggle to develop a theory of quantum gravity has long been plagued by mathematical inconsistencies. As Howl explains, ‘When you try to quantize gravity the same way we’ve quantized other forces, you end up with unsolvable infinities in your calculations.’ The problem? Gravity isn’t just another force—it’s the very fabric of spacetime itself. ‘You can’t treat it as something existing within a fixed background of space and time,’ he adds. This fundamental difference has made quantum gravity a holy grail of physics, elusive yet essential.
Quantum entanglement, a cornerstone of quantum mechanics, has emerged as a powerful tool to probe gravity’s nature. The question is: Does gravity need to be quantum to mediate this entanglement? Traditionally, scientists have thought so, assuming that entanglement between masses arises through the exchange of virtual gravitons—hypothetical quantum particles of the gravitational field. And this is the part most people miss: Aziz and Howl propose that even if the gravitational field remains classical, indirect processes involving virtual matter could still generate entanglement, albeit with extremely weak effects.
The roots of this idea trace back to Richard Feynman in the 1950s, who suggested testing gravity’s quantum nature by placing a mass in a superposition of two locations. While Feynman’s idea seemed impractical at the time, recent proposals by teams led by Sougato Bose and Chiara Marletto have revived it in more feasible forms. These experiments, which might use levitated diamonds or cold atoms, aim to detect whether two masses in a superposition become entangled through gravity.
Aziz and Howl’s work takes this a step further by suggesting that even classical gravity could produce such entanglement, though the effects would be minuscule. ‘If we detect entanglement in these experiments,’ Howl notes, ‘it would strongly suggest that gravity is indeed quantized.’ Their paper has already sparked debate, with Marletto—a pioneer in gravitationally induced entanglement—arguing that classical gravity cannot mediate entanglement via local means. She claims the study relies on non-local interactions, a mechanism she deems ‘not new.’
Despite the disagreement, both sides agree that experiments detecting gravitationally induced entanglement would revolutionize physics. ‘This could be a major milestone,’ Marletto says, predicting such experiments within the next decade. Howl hopes their work will fuel further discussion and exploration of how classical gravity might lead to entanglement. But here’s the bigger question for you: If gravity doesn’t need to be quantum to entangle matter, does this redefine our understanding of quantum gravity? Or does it simply highlight the gaps in our current theories? Let us know your thoughts in the comments—this debate is far from over.
