 Although
the publication of Einstein’s special theory of relativity led
to the introduction of space-time, this was only the starting
point for the revolution in thinking about space and time that
the theory of relativity finally brought about. The major change
came about ten years later with the publication of Einstein’s
general theory of relativity. This theory generalises
Einstein’s earlier work by dispensing with the restriction to
observers in uniform relative motion. It provides a way of relating
measurements made by observers in a state of general relative
motion.
Such
observers might, for example, be accelerating or rotating
relative to each other. Einstein realised at an early stage
during his development of the general theory that there is
some degree of equivalence between an observer who is being
accelerated and one who is subject to the effects of gravitation.Think
of your own experience of being accelerated upwards in a lift
or elevator, as the elevator starts to rise you momentarily
feel heavier than usual; the acceleration is equivalent to
an increase in the strength of gravity. Such observations
convinced Einstein that his general theory of relativity would
also provide a new theory of gravity. This realisation led
Einstein to the discovery of an important link between space,
time and gravitation.
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