More than any other scientific idea, Einstein's relativity has cemented the notion that space and time are inseparable qualities of the universe.
It began with Einstein's reworking of the classical transformation of moving coordinate systems in special relativity, and culminated a mere - but painful - decade later as he generalized and expanded these ideas to describe accelerating and gravitating systems. Space and time became space-time, or just spacetime - the cosmic fabric into which we are all woven.
But what does general relativity actually tell us about the specific properties of space-time? In simple terms the theory proposes that matter and energy influence space-time's shape, or geometry. For example, what Newton's more approximate physics calls 'the force of gravity' is really a consequence of the distortion or warping of space-time by mass - altering what the shortest paths are through a region.
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