Abstract

In 1986 Ephraim Fischbach, Sam Aronson, and Carrick Talmadge proposed a modification of Newton’s law of universal gravitation. This modification changed the gravitational potential from V = −Gm1m2∕r to V = [1 + αe−r∕λ] where α, the strength of the interaction, was approximately one percent and the range of the force λ was approximately 100 meters. This additional term was known as the Fifth Force. This suggestion was based on tantalizing evidence provided by a reanalysis of the Eötvös experiment, an early test of the equivalence principle, a difference between the measured value of G, the gravitational constant, as determined by laboratory measurements and those performed in mineshafts, and a small energy dependence in the CP-violating parameters in K0-meson decay. The two initial measurements of the Fifth Force disagreed. One supported its existence and the other did not. How this discrepancy was resolved and the subsequent history of experiments on the Fifth Force will be discussed. By 1990 the consensus was that such a Fifth Force did not exist. Despite that judgment, work continued, and the more recent history of the Fifth Force is also discussed. The consensus remains that there is no Fifth Force.