Time travel comes in two distinct flavors: the linear Closed Loop variety and the branching Open Loop variety. The first is stable and reliable, while the second is volatile and chaotic. In many time-travel stories, the reader doesn’t know for certain which variety is in effect until the end.
The Closed Loop
The Closed Loop treats time as an unchangeable dimension. Events from the beginning of creation to its end are set in stone, and the time traveler’s experiences are already worked into the equation. Essentially, time occurs on a straight line. The traveler loops back to the past, but nothing in the intervening time line changes because they always existed in that past before they actually went there.
Example: Harry Potter and the Prisoner of Azkaban by J. K. Rowling
The third book in Rowling’s iconic series, Prisoner of Azkaban introduces the time-turner, a device that Hermione uses to attend multiple classes at once. The closed-loop nature of time becomes apparent at the end of the book, when Harry and Hermione go back in time to change events, not realizing until afterwards that their future selves were already at play in the earlier disasters. There’s no alternate timeline, in other words. The reader gets to experience the same events twice alongside Harry and Hermione, but the events themselves are identical.
The unchangeable nature of a closed loop does create limitations. To the question, “Why didn’t someone use a time-turner to take out Voldemort before he got too powerful?” comes the dissatisfying answer, “Because no one did.” Everyone knows that Voldemort did rise to power, so obviously no one ever succeeded in assassinating him beforehand. To do so would create an open-loop scenario, which would destroy Rowling’s meticulously planned closed loop.
It would also negate the series as a whole, since Voldemort is the one to get the plot rolling in the first place.
The Open Loop
The open loop treats time as an ever-branching dimension, malleable and unpredictable. A change in events will cause the timeline to diverge from that point forward. This scenario requires an infinite number of universes, with the time-traveler moving from one to the next as the timeline recalibrates.
Consequently, the traveler retains memories of the events they destroy, of the alternate branches from whence they came.
Example: “A Sound of Thunder” by Ray Bradbury
I owe my comic’s punchline to this short story. It tells of a man who accidentally kills a butterfly in the prehistoric era, only to return to an alternate reality of his own time. What seems like an insignificant action causes dire consequences, for him and society both.
The open loop technically has all possible outcomes at its disposal, but let’s be honest. It’s usually the worst scenario that occurs, at least on the time traveler’s first return. If the traveler gets a chance to correct their error, things will still never be exactly what they were beforehand. “Don’t meddle” seems to be the moral of the story.
The Open-Closed Hybrid Loop
An innovative variation in time-travel stories combines open and closed loops. The broader timeline is closed, but the time traveler gets stuck in an alternating, repeating loop until they can arrive at that closed-loop outcome.
Example #1: Groundhog Day (1993)
Bill Murray stars as Phil Conners, a weatherman who gets stuck living the same day over and over and over again. He remembers each incarnation, and he tries to break the loop, to no avail. He doesn’t age, but he does retain any skills he acquires over the course of his relived episodes.
Example #2: “Endless Eight” by Nagaru Tanigawa
In this installment of the Haruhi Suzumiya series, sarcastic high-schooler Kyon relives the eight weeks of summer 15,000+ times because unwitting-master-of-the-universe Haruhi is secretly dissatisfied as the holiday comes to a close. Unlike Phil Conners, Kyon retains only a sense of déjà vu from one incarnation to the next. However, it does become stronger over time.
The short story is brilliant, but the anime version created a ragestorm among fans. The same episode aired 8 weeks in a row, reanimated each time with slightly different visual details, but with the same sequence of events. It gave viewers a taste of the time loop from Yuki Nagato’s perspective, though, as she remains fully aware for each of the 15,000+ repetitions.
The open-closed hybrid allows for the exploration of multiple possibilities with the assurance of one designated outcome. It can, however, become tedious if overdone.
Beware the Paradoxes
Please note: time travel in fiction introduces the potential for massive plot holes. Attention to detail is key when incorporating this plot element into any story, written or visual, because the audience expects the end result to make sense. As with all fantasy, time travel must adhere to rules of logic.
Shoddy time travel is the reason I despise movies like The Lake House (2006) and Kate & Leopold (2001). You can’t save the guy whose death sent you to the place where you encounter the magic mailbox that allows you to meet him two years in the past (because if you save him, you wouldn’t have gone, and then you never saved him, so you did go, but then you did save him, so you wouldn’t have gone, and then…). Similarly, if a photographer from the future flees a scene before the love interest from the future appears, said photographer can’t use a photograph of the love interest at the scene to convince her to go back in time to appear on scene.
Seriously. Get your crap together, people.
(I have been banned from watching time-travel-themed chick flicks, by the way. I’ve been banned from watching chick flicks in general, but the time-travel ones are especially verboten. Apparently I’m a killjoy.)