Precision experiments to search for the fifth force

Among the four known fundamental forces in nature, electromagnetism and gravity give rise to effects which extend over macroscopic distances, whereas the strong and weak forces act only over subatomic distances. It is natural to ask whether there can exist additional forces, particularly ones capable of acting over macroscopic distances in analogy to electromagnetism and gravity. This question is the object of intense investigation both experimentally and theoretically, in the wake of suggestions of a possible fifth force. The theoretical motivation for such a force is reviewed, along with the experimental situation in 1989