JERUSALEM, Sept. 3 (Xinhua) -- An international team of researchers has observed a long-predicted effect of gravity on a falling quantum object, showing a key principle behind Einstein's theory of gravity remains valid even in the quantum world, Israel's Ben-Gurion University of the Negev said in a statement on Thursday.
Einstein's equivalence principle is the idea that gravity affects all objects equally, regardless of mass. According to this principle, a freely falling observer should locally experience no gravitational force. However, quantum objects can behave as waves and effectively travel along more than one path, raising the question of whether the principle remains valid when "the object" does not follow a single definite classical path.
In the new study published in the journal Science Advances, the researchers tested the principle on microscopic objects governed by quantum mechanics and found that gravity behaved exactly as Einstein predicted.
The team used extremely cold atoms placed in a quantum state that allowed them to follow two paths simultaneously.
They used the Quantum Galileo Interferometer, in honor of Galileo's work on gravity. It allowed them to split the quantum wave associated with an atom into two paths, one in place (stationary relative to the laboratory and Earth) and the other for free fall, and then reunite them to see how gravity had changed the falling wave.
When the two paths were brought back together, the researchers measured a tiny change in the atoms' quantum state, and the result was the same as that predicted when Einstein's principle is applied to such a quantum wave.
The researchers said their experiment provided insight into one of the most fundamental questions in physics: how gravity, described by Einstein's theory of relativity and quantum theory, can be unified into one understanding of the universe.
The researchers noted that their finding did not prove that gravity itself is quantum, but showed that Einstein's equivalence principle still holds with quantum mechanics in the regime tested.
They added that their technique could enable future experiments with heavier objects, such as nanodiamonds, to test whether quantum mechanics could break down under extreme conditions. ■
