Posted: 19.09.2014

Einstein's geometry of space-time, based on the twin principles of relativity and 'equivalence of gravitation and acceleration' was really a reversion to the field point of view, whereby the local properties of both space and time were shown to be the direct consequence of the existence of surrounding matter, which properties in turn determined the motions of that matter.^{[1]}

Thus, according to Einstein, gravitation is an inalienable property of all masses where there is a mass, a gravitational field is generated around it in the same way as a magnetic field is created around a magnet. The structure of the field depends upon the mass and velocity of the body, and is determined by the field equation given by Einstein. Also just as the path of the motion of a piece of iron in a magnetic field is decided by the structure of the field, so that of a body in a gravitational field is decided by the geometrical structure of the gravitational field.^{[2]}

It also follows that one cannot speak of the absolute acceleration of a reference frame, only a relative one, just as it followed from the special theory of relativity that one cannot speak of the absolute velocity of a reference frame, only a relative one. Again, it is clear that inertial mass and gravitational mass are equal. For all bodies which are free of any forces will move with uniform velocity relative to an inertial reference frame, no matter what their inertial masses are, and they should, therefore, have the same acceleration relative to an accelerated reference frame. In other words all bodies irrespective of their masses would move with the same acceleration in a homogeneous gravitational field.