Scientists have directly measured a long-predicted quantum phase associated with free fall for the first time, finding results consistent with Einstein’s theory of gravity in the quantum realm. The study involved a cloud of rubidium atoms cooled to just above absolute zero and placed near a specially designed atom chip. The researchers used a device called the Quantum Galileo Interferometer to split the quantum wave of each atom into two paths. One path was held stationary by magnetic fields that pushed upward, canceling out the pull of gravity. The other path was made nearly insensitive to the magnetic field and allowed to rise and then fall freely under gravity.
This setup allowed the team to test how gravity behaves at a quantum level, using atoms as tiny test subjects, according to Yahoo News. The experiment found that Einstein’s equivalence principle remains consistent with quantum mechanics under the conditions tested, according to a report from Space.com. This principle states that, locally, the effects of gravity are indistinguishable from those of acceleration. To understand this idea, imagine being inside a sealed elevator with no windows. If the elevator is accelerating upward, you feel heavy and objects fall to the floor just like they do on Earth. If the elevator cable snaps and you are falling freely, you feel weightless. The key comparison is between an elevator accelerating upward in empty space and one at rest in a gravitational field, since an observer inside could not locally distinguish between the two situations.
This equivalence principle is central to Einstein’s theory of general relativity. The experiment did not prove a full theory of quantum gravity, but it brought scientists closer to that goal. The researchers also stressed that the experiment does not show that gravity itself is quantum. The team leader, Ron Folman from Ben-Gurion University of the Negev, said the results are an important step forward. He noted that while quantum mechanics and general relativity describe the universe on very different scales, they have never been fully unified. General relativity explains gravity on large scales like planets and stars, while quantum mechanics governs the behavior of particles smaller than atoms.
There is currently no complete theory that combines both concepts into one unified framework. The research was published in the journal Science Advances on September 2. The paper is titled “Observation of the quantum phase of free fall and the consistency with the equivalence principle.” Team member Vlatko Vedral said there is no consistent theory explaining why quantum physics should fail and that the experiment pushes quantum mechanics into the frontier of gravity.
The researchers followed the interference signal as the free-fall time reached about 2.4 milliseconds. Across 633 runs conducted over 5.3 hours, they observed 13 complete oscillations. The measured phase increased with the cube of the free-fall time, matching a prediction dating to 1927 to within about 2.5 percent.
This is a small but meaningful step toward understanding how gravity works at the quantum level, NewsBytes reported. The results show that Einstein’s equivalence principle remains consistent with the behavior of the ultracold rubidium atoms under the conditions tested.
It also opens new doors for future experiments that may lead to a full theory of quantum gravity. Researchers hope to extend the method to much heavier objects such as nanodiamonds, which could provide more demanding tests of where quantum mechanics and gravity meet.
IMAGE: Prof. Ron Folman. Photo: Dani Machlis / Wikimedia, CC BY-SA 4.0
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