139Chapter 15The General Theory of Relativity
Einstein’s Special Theory of Relativity deals with the effects of uniform
motion on the relative space and time perceptions of moving and
stationary observers. Discussion within the Special Theory of Relativity
was always limited to non-accelerated motion. As soon as accelerated
motion was encountered, as in the twin paradox, we found ourselves
beyond the scope of the Special Theory of Relativity.
It is in Einstein’s General Theory of Relativity, published in 1916,
that accelerated motion is taken into account. The General Theory of
Relativity generalizes the results of the Special Theory and deals with the
effect of accelerated motion on space and time perception. The General
Theory also deals with the effects of a gravitational field on space and
time perception by showing the equivalence of accelerated motion and
the existence of a gravitational field. This is accomplished by exploiting
the fact that the inertial and gravitational masses of all particles are
equal. Finally, the General Theory of Relativity provides a theory of
gravity, which replaces Newton’s theory of gravity.
We discovered that, within the framework of the Special Theory
of Relativity, it is impossible to determine the absolute motion of a frame
of reference through space as long as that frame is not undergoing
acceleration. Once a frame of reference undergoes acceleration, however,
it is possible to detect the acceleration because of the fictitious forces,
which arise as a consequence of the acceleration. These forces are
fictitious because, in actuality, the acceleration of a body, with respect
to the frame of reference that these fictitious forces seem to cause, is
only apparent. In actuality, the body continues to move with constant
velocity because of inertia but, relative to the accelerating frame, it
appears to be accelerating. The fictitious force causes real acceleration
with respect to the accelerating frame, however, and hence, is perceived