Fortean Times, January 2002

Time travel in Einstein's universe: the physical possibilities of travel through time
J Richard Gott III
Weidenfeld & Nicholson 2001
hb, £18.99, pp xii+291, index, bib, illus, notes ISBN: 0 2976 0760 X

As someone who cut his imaginative teeth on the time-travelling hi-jinks of Doctor Who, this is a book I've been waiting for - a comprehensive and extremely readable exploration of whether a time machine can exist in a universe ruled by relativity, quantum mechanics and entropy.

Gott, a professor of astrophysics at Princeton University, introduces the concepts and problems of time travel through familiar SF tropes, from HG Wells to Bill and Ted. As is usual in US books, the UK's finest popular time traveller doesn't get a mention, but it's still an easy appetiser for the meat of the book.

Travel into the future is relatively easy. Thanks to the effects of time dilation, all you have to do is travel into space at something approaching the speed of light, then return home. Or for the lazy, surround yourself with a shell of matter just slightly larger than a black hole of the same mass - say by crushing the mass of Jupiter into the walls of your living room. Sit in this gravity well for ten years, and you can emerge to find that fifty have passed in the outside world.

But one-way time travel is of limited interest. Fortunately, spacetime can be bent in such a way as to let you travel back in time, but only within a strictly defined interval.

This answers the question that always confronts advocates of time travel: Where is everyone? The sad truth is that time travel appears to be only possible in a time and a place where a time machine exists.

The time machines devised by Gott involve carefully choreographed cosmic strings. These infinitely long and incredibly dense strands of material are predicted by several of the competing "theories of everything", but remain strictly theoretical. Even if they do exist and a sufficiently advanced civilisation could manipulate one to create the necessary conditions for time travel, it's still a far cry from the flexibility of the fictional time machines. Gott also considers even more speculative possibilities such as wormholes and Star Trek-style warpdrives.

Despite the sub-title, the physical possibilities of time travel occupies only half of the book. The longest section applies the same physical principles to a consideration of the creation of the universe. Gott raises the intriguing possibility that a chaotic inflationary phase in the very early universe could satisfy the conditions for time travel. Part of the universe could split off and loop back to the moment of creation. Rather than creation from nothing as in the original Big Bang theory, the universe creates itself - a basic concept familiar to Doctor Who fans, if not to Gott, from the 1983 story "Terminus".

The book is finished off with a rather tangential section based on Gott's own interpretation of the Copernican principle - the hypothesis that there's nothing special about our position in the universe. Gott applies the principle to history and the likely longevity of the human race. It's an interesting if pessimistic experiment in futurology, but a statistical theory that insists that nothing we experience can be extraordinary will not endear itself to those of a fortean bent.