Scientists have detected the pull of gravity on the microscopic scale in a feat that lays the groundwork for probing its nature in the mysterious quantum realm.
In an experiment with sophisticated superconducting apparatus cooled to within a whisker of absolute zero, and copper weights taped to an electric bicycle wheel, physicists exerted a minuscule gravitational drag of 30 quintillionths of a newton on a particle of less recorded as a millimeter wide.
The demonstration paves the way for future work in which researchers attempt to measure the gravity generated by ever-smaller particles to understand how the unusual force behaves in the subatomic world where quantum rules dominate.
“We know that quantum mechanics and general relativity, Einstein’s theory of gravity, are not compatible as we formulate them now,” said Tim Fuchs, a postdoctoral experimental physicist at the University of Southampton. “The theories don’t work together, so we know something has to give, or both have to give. It tries to fill in the gaps with real experiments.”
For more than a century, physicists have tried and failed to combine gravity, which describes how mass bends space-time, with quantum theory, the rules of the subatomic world. Understanding gravity at the quantum scale could help solve some of the great mysteries of the universe, from how it all began to what happens inside black holes. But while theorists have come up with a range of promising ideas, it has been difficult to design experiments to see which, if any, nature has chosen.
In the latest work, Fuchs and colleagues at the University of Leiden in the Netherlands, and the Institute for Photonics and Nanotechnology in Italy, have come up with a way to measure the extremely subtle gravitational forces that exist between small objects.
The experiment, which was heavily shielded from interfering vibrations, centered on a magnetic particle suspended above a superconductor cooled to one-hundredth of a degree above absolute zero, or -273.15C, the coldest possible temperature. in the universe. The almost negligible drag on the floating particle was then measured as an electric bicycle wheel fitted with copper weights was rotated about a meter away, bringing the weights close to the particle and then back again.
“When you start turning the wheel, it makes the particle move, a bit like a swing. The gravitational force pulls on it, and then starts to loosen, and then pulls on it again,” Fuchs said.
The gravitational force between two objects depends on their masses and the distance between them. The bigger and closer they are, the stronger the attraction.
Write in Science advances, the physicists describe how the half-milligram particle was gently pulled by a 30-attonewton force in their experiment. An attonewton is one billionth of a billionth of a newton. “It’s definitely not quantum gravity yet, but it’s a stepping stone towards it,” Fuchs told the Guardian.
Having shown that the equipment works, the researchers now hope to measure how gravity behaves between smaller and smaller particles that are increasingly affected by the rules of quantum mechanics. But it will take some time: the first such measurements could take another five to 10 years, Fuchs believes. “This is something we should definitely explore with experiments,” he said.
