THE EQUIVALENCE PRINCIPLE

For the example of the motion of an accelerated charge it is shown tha t an inertial frame of reference in which there is a homogeneous stati c gravitational field with strength g is physically inequivalent to a uniformly accelerated frame of reference moving with acceleration -g w ith respect to the inertial frame of reference. It follows from this t hat the equivalence principle does not hold in the usual formulation. The widely held opinion that such a principle is the basis of the gene ral theory of relativity is not entirely correct. Einstein's theory of gravitation is based on an equivalence principle of a deeper content, which takes the form that the metric field g(mu nu) of a Riemannian s pace is declared to be a gravitational field. Such is the ''natural fo rmulation of the equivalence principle'' at which Einstein subsequentl y arrived.