Time travel is a well-known theme of science fiction, but is it truly achievable? John Gribbin argues that if time travel is not impossible, then it is feasible. Gribbin brilliantly illuminates the possibilities of time travel by comparing familiar themes from science fiction with their actual scientific counterparts, such as Einstein's theories of relativity, black holes, quantum physics, and the multiverse, with examples from the fiction of Robert Heinlein, Larry Niven, Carl Sagan, and others. The result is an entertaining guide to some of the Universe's deep mysteries that may leave you wondering if time indeed passes and if so, whether we are moving forward or backward. Essential reading for science fiction enthusiasts and anyone deeply interested in science.