Unifying gravity and quantum theory remains a significant goal in modern physics. Despite the success in unifying all other fundamental interactions (electromagnetism, strong force and weak force) with quantum mechanics and many attempts at explaining a "quantum gravity," scientists are still coming up short. Still, some believe we are getting closer to determining whether these two theories can be combined or whether they are truly incompatible.
A major contender for proving or disproving whether gravity is quantum is Richard Feynman's proposed experiment to test if gravity can entangle two massive objects. In theory, such entanglement would indicate quantum behavior. While it was not actually feasible to do this experiment in 1957, when Feynman came up with the idea, new scientific advances are bringing it closer to reality.
However, a new study, published in Nature, claims that it's a little more complicated than this. The researchers involved in the study determined, through their calculations, that entanglement is not necessarily evidence of quantum gravity—and that classical gravity can generate this entanglement in some cases too.
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