A while back (longer than I care to admit) I came across the term “causal loop” while researching some cool ideas for a science fiction short story. Against my better judgment I decided to write a story where the main twist revolves around a causal loop. That story is… still in the works, but I like a challenge. It’s just that causal loops have been more difficult to pin down than I thought they would be. So I decided to do some more research on them, and I discovered they’re more prevalent in science fiction than they seem. Take a look below at what causal loops are and how to use them in your fiction.

What Is It?
A causal loop is, in itself, a paradox, also considered a “predestination paradox,” and it’s specifically designed to break your brain in my opinion. These aren’t to be confused with “time loops,” which are usually when a day loops constantly. For causal loops in a story, an event happens in the FUTURE that, it turns out, has already caused something that happens in the PAST, meaning the future is caused by the past that was caused by the future… The below diagram explains things pretty neatly. Once again, thanks Wikipedia.

The future “loops” backward, sending the past into a timeline where the future that causes that past occurs. See why I’ve been having trouble writing this story? You know how science fiction and fantasy can easily be overcomplicated? Try explaining this while keeping everything simplified in your story. That’s the main thing. It’s difficult enough sometimes to enact the proper plot structure or arc, but when things are supposed to be repeated and you intentionally create a paradox, things get murkier.
So How Does It Work in a Story?
These primarily occur in science fiction. In my research, I found a few examples of how they work, mainly through this source. The short movie La Jetée, and by extension the 1995 movie 12 Monkeys, is a strong example of this paradox. In both, the protagonist’s actions trying to fix the future end up affecting the past, which is how the future happens in the first place.
Time loops, on the other hand, occur when time loops over and over again for seemingly no reason. Groundhog Day might come to mind, but stories like these have appeared as early as 1915.
How Can You Use It?
Now I don’t want to give too much away with the story I’m writing. However, I do introduce a closed causal loop that spans over centuries, so that the fantasy world naturally progressed into the science fiction world, similar to how technology has advanced in reality. The causal loop happens when a character from that past fantasy world enters the future, then comes back from the future to retrieve himself from the past and take him to the future. (Does that make sense?). I’ve mainly kept the above diagram at the forefront of everything while I write just to be sure I’m going about implementing it correctly. If you want to try writing a time loop, I suggest the following:
1) Research. Looking at examples is always the best because you can see where things have worked and where things haven’t worked. You can also tell what others have done in the past, how they went about it, and whether it made sense to readers and/or audience members.
2) Write. Like everything else in writing, you have to actually write to practice and better your technique. The same goes for introducing new concepts and experimenting with new forms. It might work and it might not work. If you fail, you know what not to do and you know when to try again.
3) Outline. Outlining helps with just about everything. I’ve kept notes in the same document just to make sure things remain accurate and simple (and it simplifies what I’m going to write next too). If you find yourself trying something like this out and discover there’s too much going on for you to remember, just write it down and keep it highlighted so it’s always available when you need it.
If you need me, I’ll be chipping away at this story again. Happy writing!
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