Classical Gravity Can Induce Quantum Entanglement, New Theory Suggests

Physicists at Royal Holloway, University of London, have advanced a significant theoretical argument proposing that conventional gravitational fields can generate quantum entanglement between matter, a possibility previously thought to require a theory of quantum gravity.

This research, led by Dr. Richard Howl and postgraduate researcher Joseph Aziz, directly challenges established paradigms concerning the necessary relationship between Albert Einstein's General Relativity and quantum mechanics. For a century, the scientific community has sought a unified framework to reconcile quantum mechanics, which governs the subatomic realm, with General Relativity, which accurately models gravity on cosmological scales. The investigation was prompted by a seminal 1957 thought experiment conceived by Richard Feynman, which suggested that if a gravitationally interacting object in a state of quantum superposition influenced another particle, it would serve as empirical proof for quantum gravity.

The new findings, published in the journal Nature on October 22, 2025, indicate that entanglement can manifest even without a fully realized quantum gravity framework. Dr. Howl clarified that the prevailing assumption held that quantum gravity was an indispensable prerequisite for gravitational interaction to precipitate entanglement. Conversely, their analysis posits that classical gravitational fields possess the capacity to induce this effect between distinct masses. In classical physics, gravity is conceptualized as the geometric warping of spacetime, contrasting with quantum physics, which maintains that fundamental forces are transmitted via discrete energy packets or quanta.

The research suggests that interactions between established classical gravitational fields and the quantum fields associated with matter can produce what the researchers term "quasi-entanglement," a less robust form of entanglement that does not necessitate the existence of quantum gravity. This effect scales differently than predictions made by theories of quantum gravity, offering information on the parameters required for experiments designed to robustly test the quantum nature of gravity. Howl noted that while a pronounced observable effect would strongly suggest quantum gravity, a weaker correlation could plausibly be accounted for by classical gravitational mechanisms alone.

The intellectual contribution provides a non-quantum gravity explanation for a potential entanglement signature, thereby refining the experimental targets for physicists seeking the ultimate theory of quantum gravity. The immediate empirical validation of this theory is constrained by the technical hurdles associated with maintaining quantum coherence in macroscopic systems, a persistent challenge in quantum information science. The research team's work offers a theoretical bridge, allowing for the re-evaluation of existing experimental results that might have previously been dismissed as noise, instead considering them as potential weak entanglement signals induced by classical spacetime curvature.