"Time travel is theoretically impossible, but I wouldn't want to give it up as a plot gimmick."
For related tropes, see Time Travel Tropes.
Time travel is a very versatile plot device. It can range from simply a device for moving The Hero from one Adventure Town to another, to a driver of the plot in itself as the characters try to understand the Nonsensoleum behind it. But broadly speaking, time travel stories can fall into the following categories:
- You Can't Fight Fate: The heroes go to the future, only to find a Bad Future where bad things will happen if things keep going the way they are in the present. So they return to their own time and resolve to prevent the Bad Future from happening. They may or may not be successful, and if they aren't, it's because, well... You Can't Fight Fate.
- Stable Time Loop: The heroes go to the past, only to realise that they can't actually change anything. Even if they interact with the past, the timeline has already accounted for it because You Already Changed the Past. Sometimes it's because You Can't Fight Fate, but in the past instead of the future. Other times, it's a Wayback Trip: the heroes go to the past, realise that history is different from what they thought it was, and then change it so that it conforms to what they "know" as history — they think they "changed the past", but history already accounted for their actions.
- Set Right What Once Went Wrong: The heroes go to the past, this time because things went wrong in the past and they want to change it to make a better "present". But there are a few variants of it:
- Make Wrong What Once Went Right: The villains go to the past to change it so that the present is better for them. Better for the villains, obviously, is bad for the heroes. It can result in a Terminator Twosome, where the heroes follow the villains back to the past to try and stop them from changing it.
- Set Wrong What Was Once Made Right: Sometimes, if you go back to the past to try and make it "better", you end up making it worse, either by accidentally making a Bad Future, invoking a Temporal Paradox or Time Crash, or drawing the ire of the Clock Roaches. If this happens, the heroes have to go back to the past and undo their own changes, which returns everything to how it was.
- Hitler's Time Travel Exemption Act: Sometimes, the story makes it impossible to go back in time and stop a Real Life bad thing from happening. Either it makes things worse (e.g. the past villain is replaced with an even nastier entity, the present loses technological and social advancements spurred by the past conflict), or time itself will prevent you from doing it. In any event, you can't go back in time, kill Hitler, and prevent World War II from happening.
- Reset Button: Something happens that changes the present, and the heroes go back to the past to prevent that thing from happening. If they succeed, everything snaps back to normal without any further intervention. Nobody will even remember that anything was ever different — not even the time travellers themselves, unless they have Ripple-Effect-Proof Memory.
- Trapped in the Past: The heroes go back to the past and get stuck there. They now have to figure out a way to get back to the future. If they can't, they have to choose between living a quiet life and trying not to interfere with the past, or using their future knowledge to make the past better. Or they might discover that they're in a Stable Time Loop and can't change anything even if they wanted to. Either way, they might make it back to the present if they take The Slow Path.
- Alternate Timeline: The heroes go back to the past and change it such that the universe splits in twain. It's a distinct separation from a Stable Time Loop in that the future will always be different because of the intervention of time travellers. Whether those time travellers can return to their "original" timeline or are stuck in the alternate one depends on the work.
- "Groundhog Day" Loop: The heroes relive the same bits of the past, over and over and over again. They have to find a way to break out of the loop and start moving forward in time again, often while using what they learned from experiencing that bit of the past so many times.
- San Dimas Time: The heroes go back to the past and have a time limit before something bad happens in the future. Normally this doesn't make any sense — presumably, you have until the future to prevent something bad from happening in the future. But in this kind of story, there's some mechanism or other that will prevent the heroes from fixing the future after a certain amount of time in the past. Sometimes this is because of a Delayed Ripple Effect — the timeline has already been changed, but the change hasn't "caught up" with the heroes yet and they can still work to fix everything before the change catches up with them and prevents them from acting further. Either way, it allows a time travel story to have a Race Against the Clock.
- Temporal Paradox: If you thought all that was complicated, you ain't seen nothin' yet:
- The heroes go to the past and successfully change history. Only problem is that they've broken causality — they've changed the past so much that it becomes impossible, in the future, for them to even come to the past. This could lead to The End of the World as We Know It and the heroes having to Set Right What Once Went Wrong. Or it could lead to the heroes jeopardising their own existence.
- The villains go to the past and successfully change history — a little too well, as they end up erasing themselves from existence or making the future worse for them in a Karmic Twist Ending.
- The heroes go to the future and find out that they can fight fate. So they resolve to prevent the Bad Future from happening — except that the only thing that would cause them to want to do that is seeing the Bad Future to begin with.
- Timey-Wimey Ball: Any of the above may be in force at any given time.
As you can see, these stories depend in part on the many variants of Temporal Mutability. The characters might expect a certain change to be possible when it really isn't, and vice versa — in so doing, they may be Wrong Genre Savvy and think they're in one type of story when they're really in another.
Whichever time travel plot you're working with, there are a few near-universal elements that you find across time travel stories:
- A mechanism by which to travel through time, usually a Time Machine. Since time travel is as speculative as Speculative Fiction can get, it usually runs on Applied Phlebotinum. There are many different ways to travel through time — some instantaneous, others not, and still others not dealing with your physical form at all. Whichever form is in use, the heroes will not really understand how it works and may struggle to get it to do what they want or to find Phlebotinum to power it. On the other hand, a Time Master will generally know what they're doing.
- A scientist or scholar who knows more about time travel than the other characters. They consider time travel an untested phenomenon and constantly spout warnings about avoiding a Temporal Paradox. They'll be particularly wary of a Butterfly of Doom or a Timeline-Altering MacGuffin, whether or not they're actually possible in that particular time travel story. They come across as Reluctant Mad Scientists a lot of the time, curious enough to want to explore a groundbreaking scientific endeavour but well aware of everything that could go wrong.
- A Mind Screw. The human mind is used to time going in a single direction at a single speed. Anything outside of that destroys the entire human conception of logic. Things happen one after another — until they don't. Any time travel story is going to deal with characters being unable to comprehend the causality they've set up. They may even encounter Time-Travel Tense Trouble. This can be mitigated somewhat with a Stable Time Loop or an inability to return from an Alternate Universe, which are the only resolutions to the story that are remotely logically consistent with the typical ideas of causality; stories wishing to be more "realistic" tend to favour these.
"Realistic" is a very weird thing to shoot for in your average time travel story. There's no reason to think that time travel is even possible in real life. Rather than realism, the aim is more for consistency; it's important that the rules of time travel make sense. But this makes time travel stories tricky to write. Too far in the direction of consistency, and you risk hopelessly confusing the audience as they try to wrap their heads around the mess of causality you've made (e.g., unintentional plot holes will become more obvious to the viewer). Too far in the opposite direction, with no consequences for casual time travel, and you risk Opening a Can of Clones—the audience won't even care about anything that happens in your plot if they suspect that a time-traveler can just change it freely in the future. (Or in the past.)
See also Meanwhile, in the Future… (for how you can run a narrative in two time periods at once) and What Year Is This? (for how your characters can deduce that they've travelled through time).
Examples of Time Travel in Fiction:
- Anime & Manga
- Comic Books
- Film
- Literature
- Live-Action TV
- Video Games
- Webcomics
- Web Original
- Western Animation
- Other Media
