ABSTRACT
Ten years before his general theory of relativity of 1915, Einstein showed, through logical necessity, how time and space are related. This, as we shall see, is where the idea of time as the fourth dimension comes in. It became known as his special theory of relativity, and it was only after he had understood the structure of this ‘spacetime’ that he could turn his attention to his general theory, in which he showed how gravity could curve it.
