THE PARADOXES OF TIME TRAVEL Sacramento （时间旅行萨克拉门托的悖论）.pdf

THE PARADOXES OF TIME TRAVEL David Lewis IME travel, I maintain, is possible. The paradoxes of of events may have two unequal separations if they are Ttime travel are oddities, not impossibilities. They separated more in one of the time dimensions than in prove only this much, which few would have doubted: the other. The lives of common people occupy straight that a possible world where time travel took place would diagonal lines across the plane of time, sloping at a rate be a most strange world, different in fundamental ways of exactly one hour of time per hour of time . The life 1 2 from the world we think is ours. of the time traveler occupies a bent path, of varying I shall be concerned here with the sort of time travel slope. that is recounted in science fiction. Not all science fiction On closer inspection, however, this account seems not writers are clear-headed, to be sure, and inconsistent to give us time travel as we know it from the stories. time travel stories have often been written. But some When the traveler revisits the days of his childhood, will writers have thought the problems through with great his playmates be there to meet him? No; he has not care, and their stories are perfectly consistent.1 reached the part of the plane of time where they are. He If I can defend the consistency of some science fiction is no longer separated from t