Phys. Rev. D 78, 022002 (2008)

Gravity is the weakest and least well understood of the four fundamental forces. It behaves well over large distances. But many theorists suspect that undiscovered particles or extra dimensions might cause its observed behaviour to break down over very short distances — which might help to reconcile gravity with the three other forces.

Current approaches will hold a little while longer, however, thanks to Andrew Geraci and his colleagues at Stanford University in California, who have made the most precise measurements yet of gravity over 10 micrometres. They found no anomalies.

The researchers placed a 1.5-microgram gold cuboid on a silicon cantilever a quarter of a millimetre long, rather like a diver on a diving-board. They then measured the extra bend, due to gravity, when a second mass was temporarily brought directly beneath the gold.