Two teams of researchers working independently of one another have come up with an experiment designed to prove that gravity and quantum mechanics can be reconciled. The first team is a pairing of Chiara Marletto of the University of Oxford and Vlatko Vedral of the National University of Singapore. The second is an international collaboration. In the papers, both published in Physical Review Letters, the teams describe their experiment and how it might be carried out.
Gravity is a tough nut to crack, there is just no doubt about it. In comparison, the strong, weak and electromagnetic forces are a walk in the park. Scientists still can’t explain the nature of gravity, though how it works is rather well understood. The current best theory regarding gravity goes all the way back to Einstein’s general theory of relativity, but there has been no way to reconcile it with quantum mechanics. Some physicists suggest it could be a particle called the graviton. But proving that such a particle exists has been frustrating because it would be so weak that it would be very nearly impossible to measure its force. In this new effort, neither team is suggesting that their experiment could reconcile gravity and quantum mechanics. Instead, they are claiming that if such an experiment is successful, it would very nearly prove that it should be possible to do it.
The experiment essentially involves attempting to entangle two particles using their gravitational attraction as a means of confirming quantum gravity. In practice, it would consist of levitating two tiny diamonds a small distance from one another and putting each of them into a superposition of two spin directions. After that, a magnetic field would be applied to separate the spin components. At this point, a test would be made to see if each of the components is gravitationally attracted. If they are, the researchers contend, that will prove that gravity is quantum; if they are not, then it will not. The experiment would have to run many times to get an accurate assessment. And while a first look might suggest such an experiment could be conducted very soon, the opposite is actually true. The researchers suggest it will likely be a decade before such an experiment could be carried out due to the necessity of improving scale and the sensitivity involved in such an experiment.