A region of space where the density of matter, or the curvature of space-time, becomes infinite and the concepts of space and time cease to have any meaning. At this point, the whole fabric of space-time ruptures and the precepts of Einstein’s General Theory of Relativity (and physics in general) break down and no longer apply, similar to the way in which a calculator returns an error when asked to divide by zero. According to general relativity, the Big Bang started with a singularity, and there is a singularity at the centre of a black hole.