In a breakthrough that paves the way for investigating gravity’s nature in the enigmatic quantum world, scientists have found evidence of gravity’s attraction at the minuscule level.

A tiny gravitational pull of 30 quintillionths of a newton was detected by physicists on a particle less than a millimeter in width, using an electronic bicycle wheel and advanced superconducting equipment cooled to nearly absolute zero.

The experiment lays the groundwork for future investigations that seek to quantify the gravitational force produced by ever-tinier particles in order to comprehend the peculiar force’s behavior in the subatomic universe, where quantum rules rule.

“We know that quantum mechanics and general relativity, Einstein’s theory of gravity, are not reconcilable as we formulate them now,” postdoctoral experimental physicist Tim Fuchs of the University of Southampton stated. “The theories don’t work together, so we know something has to give, or both have to give. This is trying to fill in the gaps with actual experiments.”

For over a century, scientists have attempted—and failed—to unite quantum theory, which explains the laws of the subatomic universe, with gravity, which defines how mass bends space-time. A quantum understanding of gravity may be able to shed light on some of the great mysteries of the universe, including how it all started and what happens within black holes. Although theorists have developed a number of intriguing theories, it has proven challenging to plan studies to determine which, if any, of these theories nature has selected.

Fuchs and associates at the Institute for Photonics and Nanotechnologies in Italy and Leiden University in the Netherlands have developed a method for measuring the minuscule gravitational forces that exist between small objects.

The experiment focused on a magnetic particle that was levitated above a superconductor that had been cooled to a temperature one hundredth of a degree above absolute zero, or -273.15C, the lowest temperature achievable in the universe. The experiment was highly shielded from vibration interference. Then, while an electrical bicycle wheel equipped with brass weights circled roughly a meter distant, bringing the weights close to the particle and then back again, the virtually insignificant force on the hovering particle was observed.

“When you start spinning the wheel, it causes the particle to move, a bit like a swing. According to Fuchs, “The gravitational force pulls on it, and then starts letting go, and then pulls on it again,” 

The mass and distance of two objects determine the gravitational pull between them. The stronger the attraction, the closer and larger they are.

The physicists explain how they conducted their experiment by gently pulling the half-milligram particle with a force of thirty attonewtons, as they write in Science Advances. One billionth of a billionth of a newton is called an attonewton. Fuchs told the Guardian, “It’s a stepping stone towards quantum gravity, but it’s definitely not yet quantum gravity.”

After proving the apparatus functions, the scientists intend to measure the behavior of gravity between ever-tinier particles, which are progressively affected by the laws of quantum physics. However, that will take time; according to Fuchs, it might take a further five to ten years for the first of these measurements. He declared, “This is something we definitely need to probe with experiments,”