This is a book about universes, a story that revolves around a single unusual and unappreciated fact: that Einstein's famous theory of relativity describes universes -- entire universes. Not many solutions of Einstein's tantalizing universe equations have ever been found, but those that have are all very remarkable. Some of them describe universes that expand in size, while others contract, some rotate like a top and others are chaotic. Some are perfectly smooth, while others are lumpy, or shaken in different directions by tides of energy; some oscillate forever, some become lifeless and cold, while others head towards a runaway future of ever-increasing expansion. Some permit time travel into the past, and others allow infinitely many things to happen in a finite amount of time. Only a few allow life to evolve within them; the rest remain unknowable to conscious minds. Some end with a bang, some with a whimper. Some don't end at all.

Our story will encounter universes where the laws of physics can change from time to time and from one region to another, universes that have extra hidden dimensions of space and time, universes that are eternal, universes that live inside black holes, universes that end without warning, colliding universes, inflationary universes, and universes that come into being from something else -- or from nothing at all.

Gradually, we will find ourselves introducing the latest and the best descriptions of the Universe we see around us today, together with the concept of the 'Multiverse' -- the universe of all possible universes -- that modern theories of physics lead us to contemplate. These are the most fantastic and far-reaching speculations in the whole of science.

Other cosmology and astronomy books focus on particular topics -- dark matter, dark energy, the beginning of the universe, inflation, life-supporting coincidences, or the end of the universe -- but this book introduces the reader to whole universes in a coherent and unified way.

John D. Barrow is professor of mathematical sciences and director of the Millennium Mathematics Project at Cambridge University, as well as a Fellow of the Royal Society. He is the best-selling author of many books on science and mathematics, including Mathletics: 100 Amazing Things You Didn’t Know about the World of Sports and 100 Essential Things You Didn’t Know You Didn’t Know: Math Explains Your World.