In order to ascertain whether gravity is a quantum phenomenon, a multinational group of researchers intends to levitate microdiamonds in a vacuum.

Long-standing theories about gravity's potential quantum nature date back to Albert Einstein's general theory of relativity, but actual testing of the theory has proven difficult.

In the event that the experiments are successful, they could finally bring theories of quantum mechanics and general relativity together, in addition to supporting some of the ideas that suggest gravity is quantum in origin.


According to the news release announcing the new experiments, "the two most fundamental descriptions of nature we have are general relativity and quantum mechanics." "The behavior of atoms and molecules is explained by quantum mechanics, while gravity is explained on large scales by general relativity."

Sadly, scientists have not been able to "unify" the two hypotheses into a single, comprehensive theory that explains how matter and energy function in our universe. This is mostly due to the impracticality of creating experiments to determine whether gravity is quantum.

An worldwide group of academics now claims that potentially ground-breaking studies intended to provide a definitive answer to this topic are finally within reach. They propose that the puzzles surrounding quantum entanglement and a somewhat unhappy theoretical cat hold the key.


The early 20th-century physicist Erwin Schrödinger set up a simple thought experiment to try and explain the difficulties with the concept of quantum superposition, where a particle can basically be in two places and in two different states at once. To put it briefly, a cat in a box can be considered both living and dead because it is impossible to precisely forecast when a decaying isotope will finally cause it to die.

“Schrödinger’s cat is a thought experiment pointing out that it would be really weird if everyday objects (and pets!) could be in a quantum superposition of being in two places at once,” explains Principal Investigator Professor Gavin Morley from the Department of Physics at the University of Warwick. "We want to push this concept to its limits."

Small amounts of atoms and molecules have been successfully put into a superposition state in the past, as Morley notes. But since the effects of gravity are too small to be detected at this scale, those efforts have included too few particles to conclude that gravity is quantum.

Morley and his colleagues intend to entangle microdiamonds of one billion or more atoms in order to overcome this puzzle. They suggest that since this should have enough mass, they should be able to gauge how much gravity affects each linked diamond. They should also observe these effects "transferred" from one entangled micro diamond to the other via superposition if gravity is quantum in nature.

According to Morley, "if gravity is quantum, it could entangle the two diamonds."

Morley described the concept as follows: "Entanglement is a unique quantum effect where two things are linked more strongly than is possible in our everyday life." "For instance, even though it's impossible to predict in advance if two coins will land heads or tails, you might find that whenever you flip them, they both land the same way up."


The scientists behind this most recent attempt to comprehend the nature of gravity acknowledge that it is an extremely challenging endeavor with many obstacles to be overcome. For instance, according to Yale University co-investigator Dr. David Moore, his group will "need to eliminate all interactions between the nanoparticles other than gravity." Because gravity is so weak, Moore explains, this kind of task is extremely tough.

The low-energy aspect of the team's experiments is one factor that is helping them. Professor Sougato Bose of University College London explains that this is because previous research on quantum gravity theories has concentrated on high-energy settings "near black holes and at the big bang." Alternatively, he states that their tests "can be regarded as the verification of a generic prediction of any quantum theory of gravity at low energies" if they are successful.

In the end, the group thinks that technology has advanced to the point where these difficult and complex tests can be carried out. Whether or not gravity is quantum in nature could be one of the most significant topics in physics, depending on the findings.

"Creating an experiment to test the quantum nature of gravity is, in my opinion, the most important problem facing physics today," stated Morley. "This new project is a thrilling step forward in that direction."

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