Physicists Directly Detect Einstein’s Equivalence Principle Acting on a Quantum Wave
Researchers have for the first time measured the predicted quantum phase shift caused by gravity on a falling atom, confirming Einstein’s equivalence principle at quantum scales.
Scientists from Ben-Gurion University of the Negev, the University of Ulm, the University of Oxford and other partners have observed a long-predicted quantum effect of gravity. By cooling rubidium atoms to near absolute zero and employing a Quantum Galileo Interferometer, they placed each atom in a superposition of two paths: one held stationary by a magnetic field and the other allowed to fall freely under gravity. After the fall, the two wave components were recombined, producing an interference pattern that revealed a tiny quantum phase shift.
This shift aligns precisely with the phase expected when Einstein’s equivalence principle is extended to a quantum wave, confirming the principle’s validity at the quantum level. The experiment does not prove that gravity itself is quantum nor does it provide a unified theory, but it offers a new laboratory bridge between general relativity and quantum mechanics and may enable future tests with heavier particles.
Why it matters
It shows that a core tenet of Einstein’s gravity still holds for quantum objects, narrowing the gap between relativity and quantum physics.
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