Meanwhile, a second torsion balance experiment in Washington has been checking the validity of Newton's inverse square law of gravitational attraction over very small distances.
Recent theories suggest that the relative weakness of gravity compared with the other forces may be due to the presence of extra dimensions: while most particles are confined in conventional space-time, gravitons are free to roam through the extra dimensions and hence the gravitational force we experience is diluted. A breakdown of the inverse square law at very small distances would be a consequence of such models.
Using a disc-shaped pendulum suspended above a second rotating disc and shielded from electrical effects by a copper membrane, the researchers have demonstrated that Newton's law holds down to distances as small as 150 mm. Even shorter distances will be explored next.
An implication of the extra dimensions idea is that the unification scale for the four forces could shift from a massive 1019 GeV to as little as 104 GeV, thereby opening up some very interesting possibilities for CERN's Large Hadron Collider (March p7). AIP