The quest to merge gravitational interaction with the principles of quantum mechanics remains perhaps the most significant outstanding challenge in modern physics. While three of the four fundamental forces have been successfully incorporated into the quantum framework, gravity stubbornly resists this unification. Within this context, the concept put forth by Richard Feynman in 1957—suggesting that the quantum nature of gravity could be verified by observing the entanglement of two massive objects—has long been viewed as a potentially crucial avenue for discovery.
However, a recent investigation, published in the journal Nature in October 2025, introduces substantial modifications to this established perspective. Researchers, whose calculations focused on theoretical laboratory setups, concluded that entanglement—which was previously regarded as an unambiguous signature of quantum gravity—might also arise under the influence of purely classical gravity, provided it is considered in conjunction with quantum field theory. Consequently, the mere detection of entanglement in proposed experiments, such as those inspired by Feynman’s original idea, is no longer considered irrefutable evidence for the existence of quantum gravitons.
The authors of this groundbreaking paper propose that classical gravitational models, when they incorporate a more precise description of matter, possess the capability to generate quantum communication and, subsequently, entanglement. This finding pivots the scientific focus away from the simple dichotomy of “quantum versus classical” toward a more nuanced analysis of experimental parameters. Previously, it was assumed that classical gravity could not induce entanglement because doing so would violate the principle of locality. Yet, the new theoretical calculations indicate that the source of this effect may reside in virtual carriers of matter, rather than being attributed to hypothetical gravitons.
The problem facing physicists has thus become significantly more complex. The immediate requirement is to develop methodologies capable of differentiating the degree of entanglement produced by classical mechanisms from that which genuinely stems from the intrinsically quantum nature of gravity. According to the scientists, the key distinction may be found in the magnitude or intensity of the observed effect. This newly defined theoretical frontier, highlighted by the publication in Nature, calls for a more cautious and rigorous approach to interpreting experimental data, underscoring the deep interconnectedness of seemingly disparate domains within physics.