Most movies or books that involve time travel deal with the premise that the time traveler can cause changes in the past that will affect subsequent events and alter the course of history. The movie Back to the Future is a perfect example of this. (Partly because it makes my point adequately, but mostly because it’s such an awesome movie that I just really want to mention it) By saving his future father from being hit by a car, Marty changes the circumstances of how his parents met. He then spends the rest of the movie plotting to ensure that his parents fall in love anyway so that he doesn’t fade out of existence. What the movie doesn’t mention is that, if Marty McFly ceases to exist, then he never could have gone back in time and messed things up in the first place, so his parents would have met, fallen in love, and gotten married just as they did before he went back in time. And then he would have been born and existed after all. But if he had existed, then he would have still gone back in time and his parents wouldn’t have fallen in love and he never would have been born and… Actually, let’s just stop this train of thought right here. It doesn’t matter whether or not the movie said anything about that because the movie is awesome just the way it is.

Anyway, that’s a pretty common theme in science fiction. Just off the top of my head, I can think of numerous books and movies and episodes of things like Star Trek and Doctor Who that have a similar theme. In my all-time favorite Star Trek episode, The City on the Edge of Forever, Captain Kirk and Spock must decide whether or not to save a certain woman (who Captain Kirk is, of course, in love with) because they know that if they make the wrong choice, the subtle alteration of history will result in World War II never happening and Hitler taking over the world. They just don’t know whether the woman’s death or the continuance of her life is necessary to stop Hitler. I think that one of the things I like most about that episode is that it acknowledges the fact that good guys from the future are just as capable of destructively altering events in the past as relatively normal people like Marty McFly, who don’t really understand what’s going on. As much as I love the show Doctor Who, I feel like it often unrealistically allows the Doctor to meddle in historical events without any affect whatsoever on the future. I can understand the concept that the history of the world as we know it has been shaped by an extraterrestrial time traveler, and that the only reason I didn’t know about all of the alien invasions in Earth’s history is that the Doctor already prevented them. I just think that if we’re supposed to think of it that way, they should explicitly say so more often. In all fairness, they do say so sometimes. The episodes Pyramids of Mars (an older episode with Tom Baker) and Blink come to mind.

This is similar to Douglas Adams’ explanation of time travel, which isn’t surprising because Douglas Adams was one of the scriptwriters for Doctor Who. In The Hitchhiker’s Guide to the Galaxy series, Douglas Adams neatly solves the problem by explaining that time is like a jigsaw puzzle. To paraphrase the general idea, the pieces fit together in the same way regardless of the order in which you attach them. If you alter the past, you aren’t changing anything about the present because the present is already there. Even if the things that you do actually do affect subsequent events, those subsequent events have also already happened, so nothing is actually changed. It makes sense if you think of time as being multi-dimensional, just like space, with an objective reality that applies regardless of where or when each individual is. If I pick up my chair and set it on top of my desk, that chair is on top of my desk regardless of whether you’re seven hundred miles away or standing right there next to me and wondering why the camaduka I want my chair to be on top of my desk. Likewise, if you go back in time to 1963 and shoot President John F. Kennedy, he’s dead whether I am also there in 1963 or here in 2012. (Please note that I’m not recommending that anyone go back in time to assassinate people. That would be evil. I’m just saying that if anyone were to go back in time and assassinate someone, the assassination has already happened)

This question of time travel’s role in cause and effect is one of the main ideas behind a book I’m reading right now, called Time and Again, by Jack Finney. I’ve actually read it quite a few times and I always really enjoy it. The book offers a theory which is essentially the same as Douglas Adams’ jigsaw puzzle analogy, although this book uses the metaphor of a twig in a river. The basic idea, though, is that time travel does not result in history being changed. However, the characters are just learning how to make time travel possible, so they aren’t actually sure about that, and that uncertainty is a central point in the book.

Douglas Adams’ theory of time is the one that makes most sense to me. For my own works of science fiction, I use a similar idea by assuming that time is three-dimensional. Maybe sometime I should write another blog post excplaining that. It works really well, because it sounds really technical and science-fictiony, but it makes the theory behind time travel so much more logical. If you’ve read some of my previous blog posts, you’ve probably noticed that I have a thing about making sense. I’m generally in favor of it.

As sad as I am to say it, I don’t really think that non-linear time travel is possible in real life. (Of course, we all travel in time linearly) Time travel serves an important role in fiction, though, partly because it’s really awesome and generally makes for a fascinating story, but also because the questions that it raises are actually relevant for regular linear time. In your life, you may never be faced with a situation in which you, like Captain Kirk, must make a choice that could result in Hitler’s successful conquest of Earthly civilization as we know it, but you will be faced with choices that could result in your failure or success in something, or that could affect details of other people’s lives in negative or positive ways. Like Captain Kirk, you might not have any easy way to know what the right or wrong choice is. Like the characters in Time and Again, you might not even know whether or not it’s really a big deal in the grand scheme of things, but you have to be aware that it could be. Like Marty McFly, you might have already made a bad decision without even understanding why it was wrong. But maybe Douglas Adams is right about everything and whatever happens is just the way things are and we don’t need to worry about the subsequent effects. I say we should trust Douglas Adams on this one; Douglas Adams was a pretty awesome writer.