Jens H. Gundlach

"The past fifteen years of laboratory-scale gravitational experimentation have been marked by many new and exciting developments. The field received a lot of impetus by the hypothesis of a ”” ... in 1986. This very testable new force would have been a blatant violation of the equivalence principle. The evidence for the 5th force was partially based on a reanalysis of the torsion balance data of of the early 1900’s. Immediately several groups around the world started to do . The availability of new technologies combined with many new and creative ideas quickly led to several refined measurements by which the 5th force in its postulated form could be conclusively ruled out. However, the physics community was once again reminded of the importance of the equivalence principle which lies at the foundation of general relativity. Tests of the equivalence principle become particularly important for , most of which predict an equivalence principle breakdown at some level. In addition it is generally believed that the can only be complete with the existence of new particles which could exist at high masses as well as at the ultra low energies. The latter frontier being covered by laboratory-gravity tests."

"We report the first results from a new that uses a 3 ton source mass which slowly rotates around the . The highly symmetric pendulum consists of a - composition suspended from a thin torsion fiber. The counter-balanced source is shaped to minimize s."

"... Newton’s revelations about gravity were motivated by the availability of quantitative observational data of the . His theory seemed to be a complete and well-proven concept and it held for centuries. It was not until the last century that Einstein derived gravitation from the underlying spacetime concept. Einstein’s work was not provoked by observational facts, but was motivated on a purely theoretical basis, which makes his formalism and prediction particularly elegant. General Relativity presented a big change in concept beyond Newton and it predicted specific phenomena. These effects have been verified experimentally and to this date are being tested to higher and higher accuracy. The classical tests were: and . Einstein’s General Relativity corrections are now being used on an everyday basis. A typical example is the , where General Relativity effects yield a combined effect of 38 per day. The accuracy to which General Relativity can be confirmed is entirely limited by experimental uncertainties and none of the uncertainty originates from the theoretical description, since General Relativity has no adjustable parameters. It seems that to date, gravity is exactly described by General Relativity."