Space and time are just as important to the structure of the Universe as the planets, stars and galaxies. Before the twentieth century, it was believed that space and time just provided the passive unchanging background against which the real cosmic drama of storms and stars was played out. It was also felt that the distinction between space and time was simple and absolute.

Different observers might choose different ways of describing the location of points in space or moments in time. By using different maps or clocks for example, or by choosing different units of measurement, such as miles rather than kilometres - but no one really doubted that each observer was describing the same space and the same time. That simple view of an absolute distinction between space and time was utterly destroyed by Einstein’s theory of relativity, one of the greatest scientific developments of all time.