Figure 5
Fig. 5. The Eöt-Wash short-range torsion pendulum experiment has tested the validity of Newton's law down to 0.2 mm (Hoyle et al. 2001), thus constraining the size of gravitational extra dimensions. Improved sensitivity would reveal violations of Newtonian gravity at shorter distances, and the weakness of gravity complicates the experiments considerably. There are several sources of background noise due to other forces that must be eliminated, and at very short distances even the Casimir attraction due to vacuum fluctuations should be taken into account.