Time Travel as a Storytelling Device

I'm a big fan of time travel stories. As most of you may know, people who can say that about themselves tend to have a hard lot in life: The majority of time travel stories are steaming piles of slapped-together inconsistencies. And when they aren't, many of them include other aspects of time travel "physics" that leave a stale aftertaste because they lessen the impact of the story. So, I thought I'd try to come up with my ideal set of rules for time travel that are engineered for consistency and comprehensibility, while not torpedoing the impact of a story.

Of course, this isn't quite that easy, so I took the time to examine various time travel theories, finally culminating in one that I personally believe gives the reader more bang for the buck than the others. Incidentally, the first I'll examine and discard is one of the more popular ones that is commonly used in comic books and serial science fiction TV.

Parallel Realities

The most popular approach to time travel these days is to have parallel realities. In short, every time a person has the opportunity to make a decision, for each of the options that person has, an additional "branch" appears. This other branch, up to the point of the decision, is identical to the reality we know. What this means is that, when someone does time travel, what happens is that they end up in an alternate "branch" which, to them, seems identical to their "home branch". In this branch, they perform all their changes.

This prevents the so-called "Grandfather Paradox", where someone goes back in time to kill their own grandfather. Now, if you really killed your own grandfather, that would mean that you would never be born. But if you had never been born, that would mean you could never have travelled back in time to kill your grandfather, so your grandfather wouldn't be dead. But if your grandfather was still alive, that would mean you'd be alive, too, to go back in time and kill him and ... at about that moment, most people, justifiedly, get a headache.

The problem with parallel realities is that it becomes pretty pointless to travel back in time to try and change something. Since the changes you make don't impact your "home reality" at all, they're only of academic interest, or a way to better your own personal lot. It's handy for deus-ex-machina-like purposes where you want to get an artefact from an alternate reality in a dangerous mission where half the people there get killed, but because it is just one reality among millions it will also have much less impact on the story's readers. It's an interesting way of foreshadowing certain things about your characters (As an extreme example, in Season 1 of Witchblade you find out that one guy is actually an undercover cop. Then at the end of Season 1 time is rolled back, so at the start of Season 2, the audience already knows this, but the main character doesn't). But while you can do nifty things this way, you can't really change time in such a world, you can only jump to another parallel reality which has effectively waited for you to do your changes.

Already-Completed Timeline (aka pre-destination)

Such a reality that waits for you to "fill in the blanks" can also be used as a general rule for time-travel in a single-timeline universe: One can assume that everything someone could do in the past had already happened by the time that person travels in time. So, if the time traveller's skeleton was found in ancient Egypt, you'd know it would eventually be transported there.

Making such a story interesting is in the hands of the author, who has to make readers wonder how it would happen and less what would happen, or tell the reader what the effects of the time travel are, but keep them in the dark about who caused those effects. That is, the reader might not even know that time travel was the cause of some of these events (a nice example of this in recent TV shows would be the whole "Babylon 4/War Without End" plotline on Babylon 5 (though, according to the dialogue in that episode, it wouldn't happen if they didn't go back when they do)).

Obviously, this again means you can't really change time in such a world. However, it can be an interesting way to e.g. resurrect a character that has died.

Freely Changeable Timeline

So, to do the really interesting time travel stuff, we need to be able to actually change the timeline. The problem that poses itself at this point is: What happens to the existing timeline that is rendered "obsolete" by the change that happened in the past?

One technique used is that everything changes instantly. People who have been "killed" by a change disappear, people who have been changed simply don't know their previous life ever happened. Sometimes, even the time traveller doesn't remember anymore. Either she snaps back to her original point in time, as if history had always been this way, or there are now two of her: The original traveller, and the new version spawned by the change (There's a nice story like this in Roger Leloup's Yoko Tsuno graphic novel "La Spirale du Temps").

This is wonderfully played for impact when the reader (and maybe even the time traveller) find out that there's now a new "self" living the life caused by the changes. It may lead to certain funny situations where there should by all means be an entire room full of the same person, though. It also means that nobody can change things for themselves, which means the kind of story that can be told in such a system would be limited. And finally, few people remember anything about the change, maybe even nobody, and thus it's hard to tell a story where one person changes time and someone else notices it, though it can certainly be done (e.g. through inconsistencies like at the beginning of "Timecop 2", where civil-war gold pops up in the present and can be dated as being too young).

In some variations of this theme, certain people are exempt from forgetting about the change in time, e.g. because they were temporally displaced themselves at the moment the change happened (an example for such an approach is the TV show Seven Days, where Frank Parker replaces his previous self in time and is the only one to remember the "obsolete" timeline) or "prior" to it, or because they were shielded by some other means (e.g. some technology of the time machine).

Alternatively, one could simply postulate that time doesn't change immediately. Rather, time changes gradually, in a wave slowly propagating from the past to the present. This can be played for mystery very well, e.g. by having people's memories gradually change. Some people may not notice, while others may figure it out. This would give a protagonist or antagonist enough time to realise what's going on and also travel through time, and can also be foreshadowed very nicely. This technique is, for example, used in Back to the Future, where Marty's family gradually fades from a photo he took in his present.

The self-correcting timeline

The changeable timeline has no safeguards against paradoxa, though. A popular approach is to claim the negation of reality or the perpetrator's removal from time when a paradoxon would happen. According to Wikipedia an alternative is what they call the Novikov self-consistency principle. Effectively, the timeline always strives for "correctness" due to statistical probability. Paradoxes are so improbable that something else always happens instead that prevents the paradox.

While this is effectively the same as the already-completed timeline for storytelling purposes (at least as it regards the grandfather paradox), it allows for relatively minor changes that do not change the present, but may allow for hidden changes to the future. Also, the time travellers themselves, being from the "present", are not covered by these self-consistency rules. Their interaction with the past is, but they them selves may die, fail, be wounded or whatever. So, effectively it's the time-travelling protagonist(s) vs. the time-travelling antagonist(s) in a free-for-all where the price is the shape of the future.

And this is where one aspect of most of the changeable timelines becomes apparent: There is a need for a clear distinction between a designated present (which is changeable) and a designated past (which lies before the present and is subject to the self-consistency rules). Consequently, time travel to the future isn't possible beyond the designated present, because otherwise the consistency rules would also have to apply there.

Of course, you could just postulate that you have several "futures" like with Parallel Realities, but then you'd have to explain what happens to these futures once the past has reached them? Do the "wrong" possibilities simply disappear? What happens to travellers from disappearing futures?

So, what's my favorite?

My current choice would be a self-correcting timeline with a slow, cascading wave for changes that don't cause paradoxes. Only people currently "outside time" (i.e. travelling) would be aware of changes once the wave has hit (if travellers didn't remember, what reason would they have to travel back?). Thus, time is changeable, we avoid paradoxes and indifference caused by parallel realities, and we can nicely have the cats panic before history changes or have nice long chases through the centuries.

Reader Comments: (RSS Feed)

Ruth Less writes: Have you ever read The End of Eternity by Asimov? That's one time travel story I quite liked. It contains a tinge of self-correction an a hint of a parallel dimension: There is a dimension outside time called Eternity. There is a way to enter this dimension and you are not affected by time while being there (Asimov does not explain how they can _act_ in this timeless world though). They speak about time as we speak about going to different floors in a house, and they can change events as easily as stepping out of an elevator and picking up an object from a room. So instead of exploring space, they do secret business with other ages on earth (e.g. importing trees from one age in exchange for antidotes from another). The discoverers of this dimension recruite young talents from all ages and teach them how to "correct time" to make the world "better". There are many specialists involved in the process of calculating and executing the minimum change to cause a maximum effect. All data about changed ages is recorded (so they might talk about he 47th version of the 92th century etc) and only the inhabitants of Eternity remember all versions. Of course they also face some problems: For example their carefully designed corrections tend to spread out like waves first, but then always trickle away quickly without any further impact on history. Also, there are ages where they cannot step out of the "elevator" at all. It seems, some other group was there "first", trying to prevent them from changing some sections of time... Eternity had a beginning, so can it have an end...? Or there's this other one, ("mister unmarried mother" or something like that?), that's making fun of all those paradoxa: It's about a pregnant hermaphrodite who turns out to be simultanously her own husband, wife, mother, father, child, the narrator, AND the person initiating the time travel that caused all that. o_O Or they one about the chess playing pair of time travelling kings... Or The Six Fingers of Time (why is the clock based on the number six?)... I've got lots of those, I can find the books for you when we meet next time...

Uli Kusterer replies: ★ I think you actually told me about some of those stories back when you first read them. I definitely remember the "mister unmarried mother" one, and the "end of eternity". But yeah, once I'm through 1984, I might check that out before I move on to "brave new world". I never got round to reading those two, so I thought it's about time I try those...

Patrick writes: Hi, Can you show me where i find a link for building a simple time machine. Thanks

bjoern writes: One of the most intense and to a certain point, where you are left unsatisfied because of a lack in physics, deepest stimulating stories about time travel is found in the low budget production "Primer". Engineers discover by learning and doing that the whole picture is far more complex (including some paradoxa) than I could have anticipated (and followed). Need to watch it again with friends to discuss and no booze. However, very recommendable. Oh Well...cheers! Bjoern (oh and if you find that link......

Merle McClelland writes: I believe the "mister unmarried mother" story you mention is "All You Zombies", by Robert Heinlein. Here's a link to the text: http://ieng9.ucsd.edu/~mfedder/zombies.html

Or E-Mail Uli privately.