An international team of physicists, which includes Nobel Prize-winning scientist Sir Roger Penrose, has observed a long-predicted effect of gravity on a falling quantum object, as reported by The Economic Times. The findings show that a key principle behind Einstein’s theory of gravity remains valid even in the quantum world, according to a statement released by Israel’s Ben-Gurion University of the Negev on a Thursday.
International Team Tests Gravity on Quantum Objects
The study, published on September 2 in the journal Science Advances, was led by scientists from Ben-Gurion University of the Negev, the University of Ulm, and the University of Oxford. Professor Ron Folman of Ben-Gurion University served as the lead author of the study.
The Quantum Galileo Interferometer Experiment
Einstein’s equivalence principle dictates that gravity affects all objects equally regardless of mass, meaning a freely falling observer should locally experience no gravitational force. While this concept is well-established for classical objects, quantum objects can behave as waves and travel along multiple paths simultaneously.
To investigate whether the principle holds when an object does not follow a single definite classical path, researchers at Ben-Gurion University developed an experimental system named the Quantum Galileo Interferometer, honoring Galileo’s historical work on gravity.
During the experiment, clouds of rubidium atoms were cooled to temperatures extremely close to absolute zero. Researchers utilized microwave pulses to place the atoms into a quantum superposition. The magnetic force was adjusted to counteract the downward pull of Earth’s gravity, and a second component received a controlled upward push before being allowed to fall freely.
This setup allowed one part of the quantum wave to remain stationary relative to the laboratory and Earth while another part underwent ordinary gravitational free fall. After the falling component followed its trajectory, the two parts were reunited to produce quantum interference, enabling scientists to measure tiny differences between the paths.
Implications and Limitations for Physics
When the two waves were brought back together, researchers measured a tiny change in the quantum state of the atoms, specifically observing the quantum phase accumulated by the freely falling part relative to the component held in place. The measured phase matched the exact value predicted by applying Einstein’s equivalence principle to a quantum wave.
According to the research team, the experiment provides the first direct observation of the particular quantum phase associated with a freely falling object in this framework, demonstrating that Einstein’s equivalence principle remains compatible with quantum mechanics in the tested regime.
However, the authors noted important boundaries to their discovery:
- The finding does not prove that gravity itself is a quantum phenomenon.
- The researchers have not unified general relativity and quantum mechanics.
- The study leaves the broader search for a complete theory of quantum gravity as an open problem in fundamental physics.
Professor Folman described the work as a step toward addressing how gravity and quantum theory might ultimately fit into a single description of nature. Furthermore, the research team stated that their technique could enable future experiments using heavier objects, such as nanodiamonds, to test whether quantum mechanics could break down under extreme conditions.
