Scientists observe Einstein’s gravity in the quantum world

For the first time, researchers have observed gravity affecting a falling quantum object in an effect predicted by Einstein’s theory. The experiment brings quantum mechanics to one of its most intriguing boundaries: gravity.

The study was led by Ben-Gurion University in Israel and included Roger Penrose, the Oxford University physicist and Nobel laureate. Researchers examined the point where two theories with very different rules meet. Quantum mechanics describes the strange behavior of atoms and other tiny objects, while Einstein’s general theory of relativity explains gravity and how objects fall.

The experiment focused on Einstein’s equivalence principle. It says that gravity should disappear locally for an observer in free fall, meaning someone falling freely inside an elevator would experience weightlessness. The researchers wanted to test whether the principle also applied to quantum objects, which can behave as both waves and particles and can effectively travel along more than one path.

Their new device, called a Galileo Quantum Interferometer, split the quantum wave associated with an atom into two paths. One path remained fixed while the other fell freely. The paths were then brought back together so researchers could observe how gravity had altered the falling wave. They used clouds of rubidium atoms cooled to a temperature just above absolute zero and manipulated near the surface of an atomic chip.

The measured effect matched the result predicted when Einstein’s equivalence principle is applied to a quantum object. The authors stressed that the experiment does not create a unified theory of quantum mechanics and gravity, nor does it prove that gravity itself is quantum. It shows that Einstein’s principle remains consistent with quantum mechanics in the regime examined. “This takes quantum mechanics to one of its most intriguing frontiers, gravity, and demonstrates once again that its predictions hold,” said Vlatko Vedral of Oxford, one of the study’s authors.

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This takes quantum mechanics to one of its most intriguing frontiers, gravity, and demonstrates once again that its predictions hold.