Time travel is a familiar theme of science fiction, but is it really possible?Surprisingly, time travel is not forbidden by the laws of physics - and John Gribbin argues that if it is not impossible then it must be possible.Gribbin brilliantly illustrates the possibilities of time travel by comparing familiar themes from science fiction with their real-world scientific counterparts, including Einstein''s theories of relativity, black holes, quantum physics, and the multiverse, illuminated by examples from the fictional tales of Robert Heinlein, Larry Niven, Carl Sagan and others.The result is an entertaining guide to some deep mysteries of the Universe which may leave you wondering whether time actually passes at all, and if it does, whether we are moving forwards or backwards. A must-read for science fiction fans and anyone intrigued by deep science.