"Universes are big at the moment." John D.Barrow.
This is a beautifully written, highly accessible account of the theoretical universes defined by modern cosmology. As Barrow comments, cosmology "is not just an exercise in describing our universe as completely and accurately as possible. It seeks to place that description in a wider context of possibilities than the actual."
Barrow takes a chronological approach, explaining the circumstances in which the various universes were proposed, and the nature of the people who devised them. The biographical information is fascinating, and Barrow's explanation of each universe is absolutely crystal-clear. This is popular science of the highest quality.