Welcome to Gaia! :: View User's Journal | Gaia Journals

We are all familiar with time travel stories, and there are few among us who have not imagined traveling back in time to experience some particular period or meet some notable person from the past. But is time travel even possible?

One question that is relevant here is whether time travel is permitted by the prevailing laws of nature. This is presumably a matter of empirical science (or perhaps the correct philosophical interpretation of our best theories from the empirical sciences). But a further question, and one that falls squarely under the heading of philosophy, is whether time travel is permitted by the laws of logic and metaphysics. For it has been argued that various absurdities follow from the supposition that time travel is (logically and metaphysically) possible. Here is an example of such an argument.

(1) If you could travel back in time, then you could kill your grandfather before your father was ever conceived. (For what's to stop you from bringing a gun with you and simply shooting him?)
(2) It's not the case that you could kill your grandfather before your father was ever conceived. (Because if you did, then you would ensure that you never existed, and that is not something that you could ensure.)

(3) You cannot travel back in time.
Another argument that might be raised against the possibility of time travel depends on the claim that Presentism is true. For if Presentism is true, then neither past nor future objects exist. And in that case, it is hard to see how anyone could travel to the past or the future.

Despite the existence of these and other arguments against the possibility of time travel, there may also be problems associated with the claim that time travel is notpossible. For one thing, many scientists and philosophers believe that the actual laws of physics are in fact compatible with time travel. And for another thing, as I mentioned at the beginning of this section, we often think about time travel stories; but it is very plausible to think that a story cannot depict things that are downright impossible. For example, it is natural to think that there could not be a story in which two plus two are five, or in which there is a sphere that both is and is not red all over. (This seems especially true if the story is told pictorially, as in the case of a movie.) Hence, if time travel is impossible, then we should not even be able to consider any story in which time travel occurs. And yet we do so all the time! One task facing the philosopher who claims that time travel is impossible, then, is to explain the existence of a huge number of well-known stories that appear to be specifically about time travel.