This video is sponsored by the YouTube RedSci-Fi Series “Lifeline”.
For ages I’ve been wanting to make a videoanalyzing time travel in fiction – not the magical or physical mechanisms by which thetime travel is supposedly achieved , but rather, the different ways time travel can influencecausality (and thus the plot) within the universe of each story.
Needless to say, there are spoilers ahead! Let's start with Ender's Game by Orson ScottCard – time travel in this book is actually 100% realistic: the characters experienceslower passage of time when they travel close to light speed, allowing just a few days ormonths to pass for those traveling while years pass on earth or other planets.
It's traveling forward through time like wenormally do, but at different rates.
This kind of time travel doesn't “change thepast” or allow characters to make different decisions than the ones they already did – it'sall one consistent historical trajectory.
The original Planet of the Apes film is similar, where astronauts experience extreme time dilation and then crash land on a strange ape-ruledplanet that (major spoiler) turns out to just be earth in the distant future.
But what about actual time-travel time travel? Well, I would say there are two big distinguishingfeatures between different types of time travel in fiction.
The first is whether or not the time traveleris there when history happens the “first time around” – that is, is there a kind of “self-consistency”where, since time travel takes you to the past, when the past happened the first time, the time-traveling version of you was always there to begin with? Or does the very act of time traveling tothe past change what happened and force the universe onto a different trajectory of historyfrom the one you experienced prior to traveling? And the second distinguishing feature is:who has free will when somebody is time traveling.
Like, whose actions are allowed to move historyonto a different trajectory, and whose aren't? One of the simplest time travels is “do-over”time travel, where you essentially get to re-play history starting exactly as it wasat a certain point, with the only caveat being you remember your experiences from alreadyhaving tried various possible future timelines (while no one else does).
It’s essentially like playing a video gamewhere you can start a level over with the foresight of what you did wrong the firsttime.
For example, in Groundhog Day Bill Murray'scharacter relives the same day over and over again, and though he can make different choiceseach time, he always starts back at the same point (except with new memories of his previouschoices).
That is, until he figures out the one exactset of choices that frees him from the loop.
I consider “A Christmas Carol” to be in thisvein, too, even though it may not seem like time travel.
But because Scrooge gets to visit the futureof his current timeline, even though he has no ability to affect the timeline directlywhile “visiting”, he can still change his actions in the present based on what he learns, essentially getting a “do-over.
” The video game Braid is built on the ideaof “do-overs”, where you get to rewind a few seconds and try something different(though there are some things that are immune to going back in time and don't “rewind”, which is what makes the game interesting).
Braid also has another kind of time travel, where you go back to your past as a separate individual, and the past version of you isthere with no free will, just doing exactly what you did the first time around, while”time-traveling you” can change the course of history.
This is also how the video “Clock Blockers”by the Corridor Digital youtube channel works.
And then there's time travel where the veryact of going to the past or future creates a fully new trajectory of history becausetime-traveling you weren't there the first time around, and now you are.
This includes the typical “anything goes”time travel movies like Bill & Ted's Excellent Adventure, Back to the Future, Star Trek FirstContact, and so on, where you can kind of instantly jump back and forth to any pointin time you want, potentially resulting in multiple versions of yourself.
From a causality perspective, anything youdo in the past (and even just the act of going back in time) redirects the course of historyonto a new timeline – in Back to the Future, Marty's interference with his parents fallingin love results in the timeline of history being redirected towards a version of thefuture where he doesn't exist and so he starts to disappear from photos and real life.
And even after correcting that major deviation, his interactions with his parents while he’s in the past result in them being very differentpeople when he returns to his present time; he accidentally caused history to progressin a slightly different direction.
The movie ”Looper” is similar, but there'sa little more circularity because when you jump to the past, you cause history to branchonto on a trajectory where, in the future, the younger you also goes back in time thesame way you just did.
Both you and your past self still have enoughfree will to change that forward course of history, though, which results in weirdnesslike you getting new memories when your past self does things you yourself didn't do, orif they lose a body part, suddenly you'll lose it too, replaced by an old scar on yourown body.
So, changes to the present affect not justfuture timelines, but also future timelines that wrap back around to the present! The indie film Primer is in the same vein, except that it takes the plot device of time travel to the extreme, with time travel withintime travel within time travel, time-traveling characters interacting with other time-travelingversions of themselves, bringing time machines with them to the past inside other time machines, and so on.
But beyond the complexity, there are two thingsthat make Primer stand out: first, time travel to the past isn't an instantaneous jump, butactually takes time: to go back 6 hours, you sit in the time machine for what feels like6 hours.
And time travel can't take you back to a timebefore a given time machine was initially activated, since of course, the machine canonly be taking you back in time inside it if it's turned on, so the first time it wasturned on is the farthest back in time you can go.
There's a nice logic to it.
Which brings us to perhaps my all time favoriteof all fictional time travel: Harry Potter and the Prisoner of Azkaban.
It's an “instantly jump back in time” kindof time travel that doesn't actually generate any new timelines.
It manages that because in this universe, while you were experiencing your initial, pre-time-travel passage through a particularpoint in history, your “time-traveling clone” was also already there, doing everything you’lleventually do when you time travel yourself.
For example, Harry and friends are saved fromdying by their time-traveling selves, the first time through that timeline.
It makes so much sense – if you go backin time, you really and truly were present at that point in time all along! This also means that during the period ofoverlap, the time-traveling you has no actual free will, since everything you do has insome sense already been done, which Harry comprehends when he realizes he has to savehis past self because he was already saved by his future self when he was in the past.
I think I love this kind of time travel becauseit manages to be logically consistent: it's time travel to the past where you can't changethe past, because the past already happened.
And there's only one timeline – the onein which time travelers arrive from the future, do stuff, and at some later date, leave togo to the past.
Logical consistency is a primary thing that, you may have noticed, I think lays the foundation for good time travel stories – not becauselogical consistency is important in an of itself, but because, most of the time, inorder to care about the characters in a story, we have to believe that actions have consequences.
If everything is just a meaningless seriesof events, then we almost don't have a story.
So it's really helpful if there are rulesby which the universe of the story functions, whatever those rules may be.
Speaking of actions with consequences, I finallygot the kick in the pants I needed to make this video from my friends at the CorridorDigital YouTube channel.
They've asked me to help promote their newYouTube Red Original Series, “Lifeline”, which, minor spoilers ahead.
is a sci fiaction thriller with time travel in it.
What kind of time travel, you ask? Essentially, if somebody dies in the future, that sends a message back to the present, which allows people to jump forward to justbefore the time the person dies and change the trajectory of history from that pointonwards, averting their death.
But as you might imagine, things eventuallygo awry.
Anyway, you can check out the first episodeof Lifeline for free on the Corridor Digital channel or by following the links onscreenor in the description .
And fun facts: I actually know the Corridor guys from back before MinutePhysics, when I was doing special effects for the “freddiew” channel.
We also all grew up in neighboring towns inMinnesota and even competed against each other in high school sports , though we didn't knoweach other at the time.
But enough trivia – go check out theirshow!.