The story of physicists' quest to answer a mind-boggling question: How can we travel through time? Since H. G. Wells' 1895 classic The Time Machine, readers of science fiction have puzzled over the paradoxes of time travel. What would happen if a time traveler tried to change history? Would some force or law of nature prevent him? Or would his action produce a "new" history, branching away from the original?In the last decade of the twentieth century a group of theoretical physicists at the California Institute of Technology undertook a serious investigation of the possibility of pastward time travel, inspiring a serious and sustained study that engaged more than thirty physicists working at universities and institutes around the world.Many of the figures involved are familiar: Einstein, Stephen Hawking and Kip Thorne; others are names known mostly to physicists. These are the new time travelers, and this is the story of their work--a profoundly human endeavor marked by advances, retreats, and no small share of surprises. It is a fantastic journey to the frontiers of physics. Some images in the ebook are not displayed owing to permissions issues.