The universe was supposed to be all there was – the whole of existence. For centuries the size of the universe & whether or not it is finite fascinated scientists & philosophers. But however big the universe may be, there being only one gave astronomers & cosmologists a headache. Existence as we know it is contingent on so many constants in nature which, if altered only slightly, would make life impossible. This seems so unlikely to happen by chance. What if, instead, there is in fact a vast range of different universes, with many variants, making ours just one of many that happens to be viable for life? In this exploration, Brian Clegg delves into the possibilities of the multiverse. Investigating questions of expanding, parallel & communicating universes, this accessible guide takes the reader into one of the weirdest & most exciting areas of modern physics & cosmology.