Is time travel possible? If so, what manner of machine would one need to traverse this fourth dimension? Covering ground similar to J. Richard Gott's Time Travel in Einstein's Universe, this slim, tongue-in-cheek treatise invokes the primary tenet of Einstein's special theory of relativity—that both time and space are elastic—to illustrate that time travel, while impractical, is definitely possible. The time travel mechanisms Davies (The Fifth Miracle) envisions are dramatically different from the devices that SF authors H.G. Wells and Ray Bradbury have employed in their fiction. All that's needed to travel to the future, noted theoretical physicist Davies asserts, is a little help from gravity and a spaceship that can reach speeds just under the speed of light. Traveling to the past is a trickier task, however, and Davies spends the bulk of his book explaining the components needed to construct a wormhole (a black hole "with an exit as well as an entrance"). Despite the author's penchant for diagrams and his habit of highlighting and repeating his major points, readers will struggle to accept some of his more difficult and extreme propositions—such as the existence of an exotic matter possessing antigravitational properties, which is vital to his construction of a wormhole. While Davies's discussion of the paradoxes inherent in time travel and of the physical laws that seem to prevent it is both thought provoking and accessible, his limited focus on wormholes may disappoint those hungering for a broader discussion of time travel technology. (Mar.)
