FULL DISCLOSURE: I’m not a scientist. I don’t know anything about time travel in real life, or how it works, or what the whole deal is with the universe. But I have noticed that time travel stories confuse a lot of people, and I have realized that most fictional time-travel can be clearly understood if we sort it into one of three primary categories. Don’t worry folks, I’m here to help.
(To avoid spoilers, I’m avoiding examples. You’ll know what you’re looking at when you see it nine times out of ten.)
Category One: SINGLE TIMELINE
Everything that future you will do in the past* has already happened. If you meet yourself, you will eventually experience both sides of the conversation. You cannot change experiences you have already had, so, if anything, your time travelling will only ensure things occur as you remember them. You’ll have the easiest time understanding this kind of time travel if you look at time from the outside – everything that will happen has happened, because time is an illusion. The past is the present is the future.
This mode is most consistent with a universe that has a guiding force, often referred to as fate or destiny. People might talk about the timeline self-correcting, too. The central tenet is that humanity’s view of time is narrow and inaccurate, which implies that a) another view exists and b) free will is an illusion. Paradoxes are very possible, because there is no such thing as an “original timeline.”
If your future self appears to you and gives you a time machine, you will use later go back in time to give yourself a time machine. There is only one timeline, the one in which you receive a time machine from your future self. Where did your future self originally get the time machine? Easy: from their future self! There’s an odd sort of cleanliness to this theory.
A fun subcategory of the single timeline principle is what I’m calling the Rewind – where timeline editing is destructive. This most often occurs when someone’s consciousness (rather than physical form) is travelling back in time. They are able to change the future, because when they go back in time there is no future any more. They might have memories of it, but those are instantly false and often fade. The Butterfly Effect is a spoiler-free example of this. The one true timeline is the last one the traveler settles on.
Category Two: MULTI-TIMELINE
Many of the more confusing time-travel stories adhere to this format, with some modifications. When you time-travel, you are leaving your universe and going to a new one. The past version of yourself that you meet is a different person, who will have different experiences. When you travel forward, you’re moving to the future of this brand new universe – you most likely disappeared entirely from the one you were in before. Maybe that universe ended all together; it’s hard to say.
Your actions now only impact the new universe. Your original universe sprouted off of this one, perhaps, but it went a different direction the moment you landed here. Thus paradoxes are impossible – your actions have no impact on the timeline that ended with your stepping into a time-machine. That already happened, it’s over. Don’t worry about it.
Now things can get wacky here, because it can often look like you’re still in your original timeline. It might seem like your actions are affecting the past you remember – maybe your memories are even adjusting. This is perfectly natural! Humans are adaptable creatures. Now that you’re in this new timeline, you’re becoming its future version of you. This is why if your past self cuts directions into his arm or if your parents don’t seem like they’re getting together, you start to change or disappear. Just because you’re not from this world’s future doesn’t mean you’re off the hook: you’re still from a future, and the odds of that future occurring are starting to change. It’s a probability game.
Look at like this if it helps (it won’t, we’re getting complicated). When there’s infinite timelines, each moment and each decision spawns a new one. Some changes are more visible than others, and every new timeline depends on the timeline it spawned from.
Let’s pretend your life is binary and assign an A or B to the big decisions in your life. We’ll say there were three of them for simplicity’s sake (though we’re far past that). Your original timeline was AAA (a 1 in ∞ chance). If you go back to your second major choice and change its outcome, you’ve halved the probability that timeline AAA will occur (.5∞ in ∞ chance) and are now in timeline AB. You still exist, obviously, so the less likely branch will still spawn, but its odds are lower. Now you go back and change the outcome of choice one, taking you to universe B. Now you’ve halved the chance of your universe existing again (.25∞ in ∞) and you’re really on thin ice. Your original universe is extremely unlikely, and the results of your first choice are now evident in all possible universes – you may start to remember the most probable one. If you kill your past self, all possible universes that ended in your time travel are cut off from this timeline, and you will disappear along with this universe – it wouldn’t exist if you never time traveled.
Ugh, that was intense. It probably still isn’t that clear to you, but I think it makes sense and I’m happy to discuss it. Hit me up!
Category Three: Subjective
Or: Timey-Wimey. This, in my opinion, is lazy writing. It can be poetic, I guess, but by and large it’s less than ideal. Doctor Who’s time travel works like this: effects of time travel are dependent on your observation of it. There’s not really any rules here. If you kill your past self, you’ll probably keep living because nothing exists outside of your perspective on it. Go ahead and fiddle about with the past: the future will change even if you’ve been there already, because all of the time stream is adhering to your personal timeline. The only real past is your past, your memory, and the only real future is that which you’ve not yet experienced.
And that’s it, as I see it! Do you think I missed any key time travel formats? What might fit into or challenge these categories? As the social media savvy say, let me know in the comments!
*Time travel is only really complicated when we’re going to the past. Forward-moving time travel is basically a high-tech version of waiting.
P.S. I’ve been watching a lot of Star Trek, and some episodes can be tricky. I submit that different methods of travel apply different categories – most can fit into a multi-timeline theory if you assume that the characters explanations for what’s happening aren’t always accurate (they’re usually best guesses any how). For instance, when Sisko, Bashir and Dax are sent into Earth’s past and seemingly prevent the forming of the Federation, we see the future being affected simultaneously. Either this is lazy, pseudo-subjective writing, or the future ship moved with them to the future of the wrong timeline. When things are set straight, we’re now in the future of that timeline, not the original. However, when the DS9 wormhole aliens/prophets mess with time, they’re working within a single timeline – same with the anomaly that sends Data’s head to the Wild West.