2005 Articles

Time Travel: Foreword

Varzi, Achille C.

Might we some day be in a position to move about in time, just as we can already move about in space? Today, few would question that deliberate change in temporal location is logically possible. On the face of it, whether time travel is a genuine possibility appears to depend on a host of tricky matters. And this is just the beginning. Many other worries arise concerning, for instance, the metaphysics of personal identity, the philosophy of action, the nature of moral responsibility, or even the logic and semantics of ordinary language. (How does tense work in the mouth of a time traveler?) Some may be inclined to think that physics, not metaphysics, should provide the appropriate setting for addressing such worries, but this is wishful thinking. Surely time travel is possible, if this amounts to declaring its compatibility with the laws of fundamental physics. Gödel’s solutions to Einstein’s field equations, for example, uncover a family of rotating universes in which one can freely move about in spacetime without exceeding the speed of light. And surely such universes are possible worlds in a thick sense—they cohere with the laws of logic and of physics. But is our world one of them? Are they ways our world could be, in a sense of ‘could’ that coheres equally well with our philosophy? In the end of the day, physical possibility may well be a subspecies of metaphysical possibility, but the drawing of metaphysical morals from current physical theories is no straightforward business.