What happens when quantum mechanics and relativity meet?

For nearly a century, scientists have speculated about the effects of free fall on a quantum wave. If their findings prove inaccurate, quantum mechanics and Einstein's theory of gravity would contradict each other irrevocably. However, testing this theory has remained elusive due to the inability to construct an interferometer capable of conducting the required measurement.

Recently, a team spearheaded by Ron Folman, a physicist from Ben-Gurion University of the Negev, along with partners from Germany, the UK, and the United States—including Nobel laureate Roger Penrose—has successfully built a novel interferometer. This device enables a single atom to follow two simultaneous paths: one involving free fall and another where it remains stationary.

Crucially, both paths culminate at the same location at the same instant, allowing researchers to gauge the impact of a falling object on a wave-like characteristic of the atom. The notion that objects are both particles and waves has been a cornerstone of physics since Galileo's era. However, quantum mechanics postulates that every entity possesses wave-like properties.

Folman elucidates, "Every particle, regardless of whether it's a car, a spaceship, or an atom, exhibits wave-like behavior." "Everything that exhibits wave-like characteristics, akin to ocean waves or sound waves, oscillates up and down." "The oscillation is quantified by a phase," he further explains. "A phase simply indicates whether an atom is at the peak or the trough of the wave."