How Does Gravity Behave Over Extremely Short Distances? A Ring Of Cold Atoms Could Tell Us, Scientists Say

This artist’s conception imagines the proposed ring of atoms as cars on a beltway. Captured and then stirred into motion by lasers, the atoms would form a “superposition”, a quantum state in which they would be simultaneously circulating around the ring and stationary. This state could allow scientists to measure motion precisely, and also potentially the effects of gravity at micrometer-length scales. Hanacek / NIST

The effects of gravity — the force that governs the motion of gigantic celestial bodies and the distribution of matter in the cosmos — are extremely hard to study over short distances. This is because at these distances — say, a few micrometers — gravity is utterly overwhelmed by electromagnetism, making it almost impossible to get an accurate measurement of gravitational forces between two tiny particles.

In order to overcome this hurdle, scientists from the U.S. National Institute of Standards and Technology (NIST) and the University of Maryland have suggested an ingenious technique. What if a ring, roughly 10 to 20 micrometers in diameter — about a tenth of the width of a human hair — were to be created? Could this ring, whose behavior would be governed by principles of quantum mechanics, be used, among other things, to study the effects of gravity at an exceedingly small scale?

The answer, according to a study published in the journal Physical Review Letters, is yes.

In the study, the researchers suggest using laser beams, which are already used to manipulate cold atoms, to arrange a few thousand atoms in a ring-like structure — one that resembles cars in single-lane beltway.

“Once the ring is formed, the lasers would gently stir it into motion, making the atoms circulate around it like cars traveling one after another down a single-lane beltway. And just as car tires spin as they travel along the pavement, the atoms' properties would pick up the influence of the world around them — including the effects of gravity from masses just a few micrometers away,” NIST said in a statement released Monday.

In addition to providing a clear picture of how gravity acts over extremely short distances, the technique, if implemented, could help answer a longstanding cosmological quandary — why does the universe appear to be expanding at an accelerated rate, when our current theoretical models tell us it should be slowing down?

Although dark energy — which scientists believe makes up nearly 70 percent of the universe — is believed to be responsible for this accelerated expansion, no sign of this mysterious force has yet been detected. The atomic ring could be used to test one of the many theories that have been put forward to explain the effects attributed to dark energy — one that states that short-lived virtual particles appear and wink out of existence constantly, and that their mutual repulsion drives the universe’s expansion.

“One possibility is that the basic fabric of space-time only responds to virtual particles that are more than a few micrometers apart, and that's just the sort of separation we could explore with this ring of cold atoms,” study co-author Jacob Taylor said in the statement.