Fifth force

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In physics, a fifth force is a hypothetical fundamental interaction (also known as fundamental force) beyond the four known interactions in nature: gravitational, electromagnetic, strong nuclear, and weak nuclear forces. Some speculative theories have proposed a fifth force to explain various anomalous observations that do not fit existing theories. The specific characteristics of a putative fifth force depend on which hypothesis is being advanced. No evidence to support these models has been found. The fifth force is also used when referring to a specific theory advanced by Ephraim Fischbach in 1986 to explain experimental deviations in the theory of gravity. Later analysis failed to reproduce those deviations.

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