The
theory built on the insights of Einstein’s first theory of relativity, the
“special theory”, one of a trio of breakthroughs that made his reputation in
1905. That theory dramatically abandoned the time-honoured description of the
world in terms of absolute space and time in favour of a four dimensional
space-time (three spatial dimensions, one temporal one). In this new space-time
observers moving at different speeds got different answers when measuring
lengths and durations; for example, a clock moving quickly with respect to a
stationary observer would tell the time more slowly than one sitting still. The
only thing that remained fixed was the speed of light, c, which all observers
had to agree on (and which also got a starring role in the signature equation with
which the theory related matter to energy, E=mc2).
