The second law states that a force is proportional to an object's mass and its acceleration. But since the 1980s, some physicists have eyed the law with suspicion, arguing that subtle changes to it at extremely small accelerations could explain the observed motion of stars in galaxies.
The key is to cancel out the acceleration of Earth's rotation, its orbit round the sun, and the orbit of the sun round the galactic centre. The basic idea was first proposed in 2007, when Alex Ignatiev calculated that the accelerations all cancel out for a millisecond at two particular points on Earth's surface, twice a year. That makes the experiment possible in theory, but not feasible.
Now, De Lorenci's team has figured out that a spinning disc can reproduce the effect any time and anywhere on Earth. Their calculations show that if the disc is positioned accurately and its speed precisely controlled, the acceleration at specific points on the disc's rim would cancel out the accelerations produced by the motion of the Earth and the sun.
If the second law is correct at all accelerations, a measuring device mounted on the rim should register no anomalous force at these points. However, if MOND is correct, the device should feel an aberrant kick. "We are able to control the conditions to produce the MOND regime in any place at any time," says De Lorenci.