An experiment confirmed Einstein's theory

An international group of physicists has for the first time observed the influence of gravity on a falling quantum object, confirming the validity of Albert Einstein's theory at the microscopic level. In a new experiment, the results of which were published in the journal Science Advances, scientists split an atom into two parts and tracked how Earth's gravitational pull changes its quantum state.

Researchers from the University of Oxford and their colleagues cooled a cloud of rubidium atoms to near absolute zero and placed them on a special chip. Using microwave pulses and magnetic fields, the specialists brought the particles into a state of superposition — each one began moving along two trajectories simultaneously. One part of the atom was held in place, with gravity fully compensated, while the other was allowed to fall freely, after which both branches were recombined.

When the waves merged, the scientists recorded quantum interference, which allowed them to measure the phase difference between the stationary and falling parts of the particle. The result fully matched the predictions of Einstein's equivalence principle applied to quantum objects. "This is a unique work combining a complex experiment with a profound theoretical interpretation of one of the most fundamental questions in physics: how to unite gravity and quantum theory into a single understanding of how the Universe works," noted the lead author of the study, Professor Ron Folman from Ben-Gurion University.

The discovery does not merge the two theories into a unified whole but proves that the laws of gravity remain unchanged even in the mysterious quantum world. Nobel Prize-winning physicist Professor Roger Penrose from the University of Oxford was a co-author of the study. The scientist believes that for sufficiently massive objects, quantum mechanics may cease to work. Although the current experiment was unable to test this hypothesis due to the small mass of the atoms, the team plans to eventually test heavier objects, including nanodiamonds (a carbon nanostructure that has the same crystal lattice as an ordinary diamond).

The equivalence principle, formulated by Einstein over a century ago, states that for an observer in free fall, gravity disappears — a person falling in an elevator, for example, would feel weightlessness. Until now, this rule had been repeatedly confirmed with macroscopic bodies, but testing it on quantum particles capable of behaving like waves and existing in multiple places simultaneously had been technically impossible. The device created by the physicists, called the "Galileo Quantum Interferometer," made it possible to overcome this barrier and for the first time peer into the junction of the two main theories of modern science.