Quantum gravity: physicists are nearing the development of a theory that could transform our understanding of the universe.

Physicists have proposed a method that could shed light on quantum gravity. Gravity is the only fundamental force in the universe that does not fit into the current quantum framework. As a result, scientists are searching for a way to develop a theory of quantum gravity that could describe all known physics. The research is published in the journal Physical Review Letters, reports Popular Mechanics.

A Theory Describing All Physics

Nearly everything we know about the universe can be boiled down to the rules of quantum mechanics. Almost everything can be described as fields, including fundamental forces like electromagnetic, weak, and strong interactions, as well as matter. However, there is one exception, and that is gravity.

As physicists have shown, gravity is not quantum, even though it theoretically should be. There is still no quantum description of gravity, commonly referred to as quantum gravity theory. To date, gravity is best described by Einstein's general theory of relativity. However, the gap between classical gravity and known quantum fields is why scientists continue to seek a way to create a so-called Grand Unified Theory that could describe all known physics, thus merging classical and quantum physics. Such a theory could completely alter our understanding of the universe.

A Method to Detect Quantum Gravity

The authors of the new study proposed a method to test the existence of gravity in the quantum realm. According to the physicists, instead of attempting to prove the existence of quantum gravity, one can disprove purely classical gravity by showing that the measurement of this force adheres to at least one quantum rule: superposition.

The physicists suggest creating a tiny nanocrystal and placing it in a state of superposition. This quantum state is where any object, most often a particle, exists in multiple states simultaneously until it is measured.

The authors of the study state that since quantum mechanics is defined not only by the principle of superposition, the observation of quantum entanglement would imply that gravity is described by either quantum mechanics or an unknown theory of non-classical physics that adheres to the principle of superposition. To determine if gravity is indeed quantum, other postulates of quantum mechanics need to be tested concerning gravity.

The Quantum Nature of Gravity

Scientists believe that once a state of superposition is created, two actions must be performed. First, to create a sort of control group, the crystal in the state of superposition must be measured to determine its final state. Next, another identical nanocrystal should be placed close to the first one so that a very weak gravitational force arises between them.

Theoretically, the first crystal in the state of superposition should feel the gravity of the second crystal. Physicists will then measure the first crystal again to see if its final state differs from what it was before the second crystal's interference. This effect is caused by a phenomenon known as quantum disturbance, which occurs only if quantum effects are at play.

According to physicists, if the state indeed differs, it will be the first evidence that gravity truly has a quantum nature. While this will not yet be complete proof of the existence of quantum gravity, it represents a significant step forward in understanding it.