Introduction

Abstract

The originator of the general theory of relativity was Einstein, and in 1919 he wrote1: The special theory, on which the general theory rests, applies to all physical phenomena with the exception of gravitation; the general theory provides the law of gravitation and its relation to the other forces of nature. The claim that the general theory provides the law of gravitation does not mean that H.G. Wells’ Mr Cavor could now introduce an antigravity material and glide up to the Moon, nor, for example, that we might produce intense permanent gravitational fields in the laboratory, as we can electric fields. It means only that all the properties of gravity of which we are aware are explicable by the theory, and that gravity is essentially a matter of geometry. Before saying how we get to the general from the special theory, we must first discuss the principle of equivalence.