A Beginners Guide to Time Travel

Time travel is a curious tool in the sci-fi genre. Authors can use it for amazing, mind-bending stories. However, more often than not, it just confuses the audience. Avengers Endgame was a masterpiece, but scrutinizing the time travel too closely leads only to headaches. This guide to time travel for beginners should acquaint any sci-fi enthusiast with the basic tropes, mechanics, and principles of time travel.

Three Main Types of Time Travel

Overall, there are three main types of time travel in fiction. These three different types are open-loop time travel, closed-loop, and parallel-dimensions. Each type has its use, and each lend themselves towards different kinds of stories. In this beginners guide, we will cover each major type of time travel in turn.

Open-loop

Open-loop time travel is what most people think of when they think of time travel. Here, going into the past can change the present and future. The further you go, the more profound the effect. These stories are best when writing about changing the present. One example, albeit an odd one, is A Christmas Carol. In this story, Scrooge sees a future in which Timmy dies. It is stated that this is all because of Scrooge’s greed. So, if Scrooge changes his actions, Timmy will survive. Scrooge’s actions matter.

Closed-loop

Despite open loop being more well-known, closed-loop time travel is more common in stories. This may be because closed-loop time travel is similar and is a whole lot less confusing. In a closed-loop, the past cannot be changed. Instead, there is one consistent timeline. If you went back to the past, you already went back. So, your presence can’t change anything.

That felt complicated even to me. So, let’s use an example: Harry Potter and the Prisoner of Azkaban. 

In Prisoner of Azkaban, Harry Potter and the gang are assailed by dementors. All fall unconscious, except for Harry. There he sees his father cast a spell and save all their lives. Then, they go to the hospital wing and grab a time-turner for some time-travel shenanigans. In the woods, Harry tries to see his father. He then realizes he saw himself and cast the patronus spell that had been beyond his power. The time travel in Prisoner of Azkaban is closed loop because the effect of Harry’s time traveling actions were already fully incorporated into his prior experiences.

So, in a closed-loop, time-travel can have an effect. However, when someone returns to the present, the past will not have been altered. Closed-loop time travel causes the fewest headaches.

Parallel-Dimensions

In the parallel-dimensions type of time travel, when someone makes a change while in the past, it spawns a parallel dimension. So, there will be two dimensions: one where someone went back in time and changed something, and another where this didn’t happen.

A notable example- in fact, the notable example- is Avengers Endgame. In Endgame, time travel isn’t exactly consistent, being a blend of all three main types of time travel. Still, parallel-dimensions defiantly play a role. In the movie, the Ancient One states that the Infinity Stones anchor the timeline. If a time stone is removed via time travel, then another dimension will spin-off. And it will be a much darker future.

Time Travel Subtypes

Of course, most time travel stories are very complicated, using multiple types and subtypes. Time travel is messy, a confusing mess filled with an author’s ideas and random garbage they found on the street. In all its complexity, it seems that time travel, like time itself, is fluid. And of course, there are many more types and subtypes and the like. I found this video very illuminating. So, next in this guide I’ll briefly cover time travel tourism and time-loops.

Time Tourism

Time-tourism is a subgenre of closed-loop time travel. This subtype is characterized by going into the past and often meeting famous characters. These stories are different from most others as people don’t go into the past to change anything. They go into the past to learn about and watch people.

There are two other differences. One, the characters rarely meet alternate versions of themselves. And two, oftentimes, time travelers can’t make any changes. This is in contrast to most other closed-loop time travel. There, time travelers can have an impact on events. Their actions just won’t cause any changes in the present. In time tourism, the effect of characters’ actions is neglected.

Time-loops

In contrast, time-loops are a subtype of open-loop time travel. And, this is a pretty well-known trope. It’s the main gimmick of Groundhog Day, makes an appearance at the climax of Doctor Strange, and appears as a one-off in many other pieces of fiction. Essentially, in a time loop, characters will repeat a scene or a day until they find a way to ‘fix’ their problem and find a solution.

The Butterfly Effect

The butterfly effect is a common idea and essential to cover in any time traveling guide. The belief goes that any small act can have far-reaching impacts. If a character goes back in time far enough- and if they are in the right type of time travel- then their future can be radically altered.

This often leads to characters being extremely, sometimes absurdly, cautious when in the past. One wrong move could send everything into a disaster. Take Harry Potter and the Cursed Child as an example. This play is, for some inane reason, open-loop even though the rest of Harry Potter was closed-loop. In the Cursed Child, the main characters jump back in time to save Cedric Diggory. But every time they go back, the future that they come back to is radically altered. 

With the butterfly effect, the characters are always striving to keep reality as it is while changing one specific thing. This is impossible as history is but a tangled tapestry, and pulling on one thread tugs equally hard on many others. The characters almost always come back to an alien world. And they are always unsatisfied.

Grandfather Paradox

The Grandfather paradox is quite well known. It follows thusly: A time traveler goes back in time to kill his grandfather. He succeeds. But, how is this possible? For, if he successfully kills his grandfather, then he is not born and therefore not able to kill his grandfather.

Let’s analyze it from the point of view of the three main types of time travel.

1. Closed-loop

The person will be unable to kill their grandfather. There are a few possibilities, including the time traveler somehow being physically unable or simply being adopted.

2. Parallel dimension

If someone goes back in time and kills their grandfather, then this will only be true in one dimension. One will have the grandfather and time traveler, and the other won’t. Here, it’s simple.

3. Open Loop

This is where we run into problems. What happens most often is that this doesn’t change anything. The paradox has no effects. To explain how this works, I’ll just use some of my own ideas that I’ve drawn out of the ether.

When someone goes back in time and changes the past, things change in the present/future (in an open-loop). This means that everything happens differently. So, if everything happens differently, what reason would the person have to go back in time to change time? As much as it is casually known, authors seem not to actually use it or think about its ramifications.

Of course, there are other things authors can include, from changing memories to breaking reality, or the timeline correcting itself. Time travel is complicated.

Consistanty & Complexity

I’ll close out this beginners guide to time travel with complexity. Complexity is the bane of time travel. After all, time travel involves messing with the continuity of the story. It is far too easy to bend the rules of time travel or make them so convoluted that it’s hard to follow along. For example, I can’t quite explain how time travel in Endgame works. This isn’t to say that the movie wasn’t good, just that it was confusing.

The two Harry Potter time travel stories handle traveling back in time differently. And don’t get me started on the Cursed Child. I’ve used it as an example above, but it completely ruins time turners. Prisoner of Azkaban was closed-loop. But, the Cursed Child depends on it being open-loop.

Really, writing about time travel is hard. It opens up a can of worms that can’t really be closed. It is a dangerous tool and one that should be wielded carefully. I hope this discussion of time travel for beginners helps you do just that.