Time travel has been one of the enduring staples of science fiction ever since H.G. Wells wrote The Time Machine in 1895, right up there with little green men and ray guns. Einstein's theory of relativity lent credence to the idea that time is not absolutely linear but could be bent, reshaped, or even re-entered like a river. The twentieth century saw an explosion in popular discussion of the paradoxes inherent in time travel - from the idea that those moving at the speed of light might return "before they left" to the possible permutations associated with the ability to "change" time. From killing one's grandfather, marrying one's mother, preventing Hitler from being born (or assuring that the Nazis won the big one), time travel offers some wonderful brain teasing puzzles.
The Best Time Travel Stories of the 20th Century attempts to collect some of the century's best time-traveling short fiction. Featuring authors such as Paul Anderson, Ray Bradbury, L. Sprague de Camp, Jack Finney, Larry Niven, Joe Haldeman, Nancy Kress, Ursula K. LeGuin, Robert Silverberg, and Connie Willis, this book spans not only the decades but the gamut of approaches to both time travel and science fiction itself.
In R.A. Lafferty's "Rainbird," an inventor is so brilliant that he manages to come up with a way to go back and give himself a head start - only to discover that if you go to the well too often, it ends up dry. Ray Bradbury's "A Sound of Thunder" explores both the commercial exploitation of time travel (for purposes of hunting extinct creatures) and the possible paradoxes associated with altering the past. L. Sprague de Camp explores the "hunting dinosaur" theme with a bit more humor as his protagonist explains why he won't take a particular person hunting a Late Mesozoic dinosaur in "A Gun for a Dinosaur." In "Yesterday was Monday," Theodore Sturgeon reinvents the idea that "all the world's a stage," and each of us are but players in it with a sci-fi time travel twist - as a player finds himself stuck backstage on Wednesday when it really ought to be Tuesday.