Fifth Force from Fifth Dimension

Using a novel coordinate system, we rederive the eld equations and equations of motion for 5-dimensional relativity in the general case where the metric can depend on all 5 coordinates (i.e., Kaluza-Klein theory without the cylinder restriction). We show that in general the fth dimension produces a new dynamical force in 4-dimensional spacetime. This timelike fth force is proportional to the 4-velocity of a particle and is thus unlike any known 4-force. We brie y examine the properties of some simple models, and suggest that the detection of the fth force is the most promising way to investigate the existence of an extra dimension in nature.