Space-time. Often described as the fabric of reality, this four-dimensional amalgamation of space and time was set at the heart of physics by Einstein (see "How to think about… Relativity"). But what is it?
A popular way of envisaging space-time is as a stretchy rubber sheet that deforms when a mass is placed on it, with the varying curvature analogous to the warping of space-time by gravity.
It's a picture that might lead us to believe space-time is itself something physical or tangible. But the physical manifestation of the dimensions we move through is, if anything, the fields they contain (see "How to think about… Fields"). For most physicists, space-time itself is a lot more abstract – a purely mathematical backdrop for the unfolding drama of the cosmos. Martin Bojowald of Penn State University in Philadelphia sees it as a mathematical entity ...
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