Scientists have measured gravity at an extremely short distance, in what they hope will tell us more about extra dimensions.
Published in Physical Review D, Japanese researchers used the world’s highest intensity neutron beamline facility at the Japan Proton Accelerator Research Complex (J-PARC) to probe gravitational interactions at just 0.1 nanometers.
According to Newton’s law of universal gravitation, the gravitational force between two objects is proportional to their masses, and inversely proportional to the square of the distance between them. This is known as the inverse square law (ISL).
We can see this at large scales, namely through objects in the universe, such as the ones orbiting our Sun. We’ve also seen that it holds true down to less than 1 millimeter. This experiment, however, provides a new insight into what happens when you approach quantum levels.
“There are numerous effects suggested by accepted theories of gravity over short distance ranges that could be borne out by experiment,” a co-author on the study, Tatsushi Shima of Osaka University, said in a statement.
“By successfully extending the search range of an exotic gravity down to short distances of [about] 0.1 nanometers, we have been able to demonstrate the highest sensitivity reported to date, producing experimental data that will help to unravel the proposals.”
J-PARC is a series of proton accelerators, smashing together beams of protons at the speed of light. Its neutron beams are the highest intensity in the world, using a pulsed proton beam to achieve their high intensity.
In this experiment, pulses of neutrons were fired into a chamber filled with helium or xenon gas. The researchers measured how long it took the neutrons to travel through the gas, and also watched how much they scattered.
Based on the scattering, they found that no unexplained force was acting on the neutrons below 0.1 nanometers. In other words, this appeared to be the lower limit at which gravity works. Which is kind of neat.
In their statement, the team also noted that this "will help shed light on whether the space in which we live is limited to three dimensions." The idea is that in string theory, all the dimensions are packed into a really tiny space. As gravity is not as strong as the other forces, it leaks into the other dimensions, so they're hoping to see some of the effects of this in action.
"The large extra dimension (LED) model is famous due to its unique feature of giving a simple explanation to the extreme weakness of the gravity compared to the other fundamental interactions," Tatsushi Shima from Osaka University, one of the study's co-authors, told IFLScience. Using neutrons allow them to get to much shorter distances, and probe this more closely.