Having just gotten a notification from wordpress that I registered my blog a year ago today (though it looks like my first entry was published on the 12th) and seeing as I’m at 99 published entries, now seems a novel time to publish entry number 100, and to share some thoughts on time travel, as we are on the topic of time.
I was discussing the possibility of time travel with a friend the other day, and I brought up a pretty decisive point that a professor once shared with me. The idea is that time travel is logically impossible, because it entails that, if I went back in time to 1968 (a most interesting year, in my opinion, due to the civil rights movement, politics and music), stipulating that the population of New York City was 7,000,000, it would be the case that the population of NYC is 7,000,000 and the case that the population of NYC is not 7,000,000, it is 7,000,001. In other words, history is constituted of facts about what happened, and time travel involves contradicting those facts by making other facts the case.
To those who say that time travel changes the course of history, and that’s an understood consequence of time travel, I’d say you’re missing the point. Time travel movies and TV shows have the famous warning to characters not to interfere in events, lest they alter history. But this misses the point that their presence, whether detected or not, has changed facts about history, regardless of whether the consequences are noticeable upon their return. All that history is, in an important sense, is a collection of facts, so if one’s presence changes the facts of the time then it only makes sense that one has not actually gone to the year 1968. The point of all this is that time travel is inherently contradictory – we cannot travel back in time, to 1968 or elsewhere, but we can be taken into a simulation of what 1968 was like or an alternate reality of 1968, with everything identical save for the details and facts involving the time travelers. Whether actions in this simulation or alternate reality have far reaching consequences for present reality is another question altogether, and one best left to sci-fi films.
During that discussion I articulated another reason why time travel is contradictory, and it is this reason that I am eager to share today. In order to travel back in time it must be the case that time is not one-directional. This is a big assumption in itself and one that I think is useful to bring to the fore because it reveals how paradoxical time travel is. Let us imagine that in four years I create a time machine, and I go back to the year 1968. In order for it to be genuine “time travel” it will have to be said that it becomes a fact that I was alive in the year 1968. If it becomes a fact in four years that I was alive in 1968 then it is a fact right now that I was alive in 1968. But even stipulating that I do create a time machine and travel back in time to 1968 in the future it wouldn’t be a fact right now that I’ve been alive in 1968. I can’t actually go back in time to 1968 without it always being the case that I’ve been alive in 1968, but that seems false, as I would only have come to be alive in 1968 in 2018. So again, what this suggests is that traveling back in time to 1968 is impossible, and at most one can go to an alternate reality with a different course of history, and this is enough to avoid saying that I’ve ever been alive in “the real” 1968 and with it that I’ve always been alive in 1968.