David Weld: Cavendish-type experiments

David Weld from Stanford spoke about their Cavendish-type gravitational experiments. At distances around 20 microns, they can rule out a new force that would be 10,000 times stronger than gravity. In other words, if you parameterize the potential energy as gravitational plus Yukawa,

• E = G . M . m ( 1 + alpha exp (-r/r0) ) / r
  

then assuming that r0 is around 20 microns, they can experimentally show that the absolute value of alpha must be below 10,000 or so. The paper about their previous experiment is here and we described it here. Unlike the torsion balance experiments (see also Eot Wash), their apparatus is spinning rather quickly. The apparatus involves piezoelectric bimorfs, laser interferometers, motors that work at low temperatures, cooling system, and many other things. We have discussed the submillimeter experiments many times which is why I won't repeat the details now.