Neutron Test for Newton’s Gravity

Newton’s law of universal gravitation predicts that the gravitational force between two objects is proportional to the objects’ masses and inversely proportional to the square of the distance between them. The law, which applies to weakly interacting objects traveling at speeds much slower than that of light, has survived test after test. However, some quantum gravity theories anticipate that the law might break down at small distances. Now, through experiments with a pulsed neutron beam, Christopher Haddock of Nagoya University, Japan, and colleagues have checked Newton’s law on subnanometer scales. So far, the team has found no deviations from Newtonian predictions.