Gribbin sets out to explain how time travel is theoretically possible and looks at the various different ways which might allow it. He pays particular attention to the most likely time-machine: that provided by the concept of the "wormhole". Like a tunnel through space and time, a wormhole could connect different regions of the Universe which occupy both different spaces and different times.

The story is given a historical context and the necessary background from Newton onwards for the reader to understand the concept of warping space and time, dense neutron stars and black holes. From here the science theory becomes as strange as science fiction and the two are intertwined. Carl Sagan kick-started the whole idea with his 1968 book Contact and making hyperspace connections though spacetime. As Gribbin writes, the science fiction version was on the right lines: "Hyperspace connections do, at least in theory, provide a means to travel to the far distant regions of the Universe" without spending vast amounts of time "pottering along through ordinary flat space at less than the speed of light". The story continues through white holes, worm holes and spacetime tunnels.

A useful glossary, bibliography and index help the intrepid reader negotiate these fringes of reality. --Douglas Palmer

Synopsis
Once the stuff of science-fiction novels, black holes, and their even stranger cosmologican counterparts, white holes and wormholes, are now the subject of serious inquiry. Physicists who formerly shunned these astrophysical eccentricities have begun to theorize about them and search for the physical proof of their existence with the zeal of converts. The unavoidable conclusion of this research is that these "rips in the fabric of spacetime" are not only real, they might actually provide a passage to other universes and travel through time. This book tells the story of the theories and discoveries that have led scientists to these conclusions.