Models of Time and Fate

There are many models of time and time travel. In this guest post, Gregory Taylor goes through the principles of some of them and explains how they deal with free will and fate.

This fascinating post on time travel models and fate comes to us thanks to Gregory Taylor.

Gregory B Taylor
Gregory B Taylor

Gregory’s qualified in maths (major in Computer Science and a minor in Music) and education in teaching Maths and Computers. And in his spare time he writes.

So after reading his article below, why not check out his serial personifying mathematics (which has now become a webcomic) and keep an eye out for Time & Tied where teenagers discover a time machine.

Now. Back to our fate!

Models of Time and Fate

How inevitable was this post? As both a writer and reader of temporal fiction, one thing that I find myself becoming more interested in of late is the psychological impact the existence of time travel would have on us. Do we want the power to change our history? Or our destiny? As a time traveller, would we even be in control? Or are we at the mercy of fate, forced down a particular path no matter what!

To that end, here is a summary of the most popular time travel theories that exist, combined with a look at how the timelines might be affected by what we’d consider “fate” (events beyond our control) and “free will” (the power to act voluntarily). Bear in mind that my degree is in mathematics, not psychology, and I’d be very interested in alternative interpretations or related discussion on the matter.

The Fixed Timeline

The “fixed timeline” model claims that anything which has happened in the past always happened that way, regardless of (or despite) the existence of time travel. The simplest version of this theory would have our time traveller unable to interact. They are a “ghost”, an unseen “observer” to history.

However, it is equally possible to have a fixed version that would allow interaction, yet has the time traveller’s upcoming actions already etched in history. For instance, that time Bill fell out of a tree and broke his arm? It was due to events yet to occur in his future; perhaps Bill will go back to prevent it, which is what causes the fall.

At first glance, this theory would seem to say that all events are fated to occur, and by extension, that we lack free will. Effectively what will be, already has been, and our time traveller is destined to act the way he did. To me, this seems too rigid. Consider that this theory employs the “Novikov self-consistency principle”, and that principle merely states that any event giving rise to a paradox has zero probability of occurring.

This is not quite the same as saying that everything is fated.

Consider, what if the fixed timeline model merely means “the time traveler’s present cannot change”? For instance, say Ted loses his keys. He time travels back, seeing when he dropped them, and retrieves them. So Ted was always the person who walked off with his own keys, right?

Maybe not. Perhaps there was an overwritten timeline where the keys were washed down a storm drain, lost for good. Ergo, by going back in time and retrieving them after the loss – but before that event – Ted has indeed changed history. The storm drain event never happened. Except… Ted doesn’t realize he changed anything. He has the free will to believe he has changed history (because he has?) even though his memory might tell him otherwise (the keys were never lost?).

The main thing about the fixed timeline theory is that we can never know whether we have, in fact, made changes. Sure, Ted’s future will be different whether he has his keys or not… but for him, nothing changed up to the point when his time travel occurred. Going back to Bill falling out of the tree, did it happen because of a squirrel in the bushes? Because, in time travelling back, Bill’s future self could scare off the squirrel, but by him now being in the bushes instead, the fall still occurs. Until Bill decides to take the trip or not, we don’t know the precise cause for the inevitable effect.

That’s the fixed timeline. We retain a measure of free will in our actions, and yet the events of the past are never in doubt. Even though the probability that you will shoot your ancestors is 0% (see Grandmother Paradox below), there are still any manner of other things you can have done while in the past. Assuming you choose to go. It’s only when the outcome of our trip is uncertain that we must look at:

The Dynamic Timeline

The “dynamic timeline” model allows paradox. It does not require paradox, but by removing fated outcomes, paradox naturally follows. Lorraine goes back in time and kills her grandmother, Maggie. (Because aren’t you more likely to be sure of ancestry on your mother’s side?) But this means Lorraine is never born, so she can’t go back and kill her grandmother, so Maggie lives her life, Lorraine is born, and then she goes back in time and kills her grandmother…

There are, in fact, a few ways out of this dilemma. A common plot device is that there is some sort of “time delay”, allowing a person to realize they messed up, subsequently fix their mistake, and thereby restore stability to the timeline (with perhaps minor changes). “Back to the Future” is notorious for this. Alternatively, a person may return to a changed present (perhaps from mental time travel), and that’s their motivation for going back to restore the original version. It’s as if some incarnation of time is giving the time traveller a choice (free will) – do I really want to screw up the universe that way?

Because there is another way out of the paradox, if the time traveler does not act. Consider: Lorraine goes back in time and kills her grandmother, Maggie. But that means Lorraine is never born, so one day Biff starts hearing voices and is compelled to kill this woman named Maggie (before Lorraine can), and so he does that, the end. Paradox resolved. The only casualty is Biff’s free will; he was forced into temporal homicide by the actions of Lorraine, someone who (strangely enough) will never actually exist within the final dynamic timeline. Could all of our strange compulsions be a result of time travellers?

This gets messier if Lorraine interacts with her past self instead of Maggie. Presumably, one of the Lorraines then negates her own existence and fades away, or is instead revealed to be a hologram, robot double and/or product of dementia. Even so, I suspect it is still possible to break out of any infinite loop that might develop – at the expense of someone’s free will. The only alternative (that I know of) for breaking out of paradoxes with free will intact is:

Multiple Timelines

The “multiverse” model allows alternate timelines. Leonard burns dinner, thus goes back in time half an hour to take it out of the oven, thus has no reason to go back in time, so wait, who took that dinner out of the oven? A fixed timeline says the dinner was never burned, Leonard always went back to get it (closing the loop). A dynamic timeline says the dinner was burned, but past Leonard will fade from existence at the change (nullifying the paradox). Multiple timelines say there now exists a timeline where dinner was burned, and one where dinner was not.

We have regained total control over our fate, possibly at the expense of our sanity – because the timeline with the burned dinner now no longer has a Leonard in it, while the one with the unburned dinner contains two. And what if both those Leonards now travel back in time?! (It seems to me that, at the very least, there must be some exchanging of mass at temporal displacement in such cases, with Leonard-sized chunks of matter appearing in the burned dinner timeline when he leaves, to compensate for the imbalance…)

As with dynamic timelines, there are narrative ways to reduce the cataclysmic effects of new timelines branching out. Small jumps may be impossible (less than a million years), meaning there is time to smooth out the effects, while making the whole exercise impractical. Or history might be hard to reroute (temporal inertia), implying that similar timelines phase back together. Which is bringing fate back into the equation.

In any event, it does seem like the model with the least stability is equally the one with the most free will. Which I suppose makes sense. But is that a reality we can accept?

Recursive Timelines

It’s worth mentioning another model, that of time loops. Not the paradoxical moebius-strip loops of the dynamic timeline, but an untwisted version, where over and over, events repeat themselves, with most of the universe being none the wiser. These turn up a lot in episodic television shows – so much so that I once created a webpage to list them.

The idea that such a repetition can happen is interesting because, while it is often situational (meaning rarely intentional) and seemingly fatalistic (with actions constantly repeating no matter what), one can usually break out of the loop by behaving differently. By exercising free will. Which begs this final question – is it free will if one MUST behave differently? It’s things like this that make me think a physicist must consult with a psychologist, to properly understand the repercussions of time travel.

Hopefully you enjoyed my look at these temporal theories. If so, you might also enjoy my serial, “Time & Tied“, where characters occasionally argue these points back and forth. (But not that often, because the majority of the cast are teenagers, who know little about the future war which is subtly intruding on their present day.) But whether you investigate my fiction blog in our particular timeline or not, I do thank you for at least reading this post, and Paul Wandason for giving me the opportunity to write it.

Gregory B Taylor

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Que sera sera. Is Destiny really Fixed?

Darth Vader and Doris Day would make a good couple – they both believe the future is fixed. If that’s the case, the need for time travel may be under question. What do we expect from time travel if our destiny is fixed and the past cannot be changed?

Darth Vader and Doris Day would make a good couple – they both believe the future is fixed. And if that is the case, the need for time travel may be under question.

Que sera sera – Whatever will be will be.

Or as Darth Vader said…It is your destiny.

The future is fixed. You can’t change it. Get a grip and deal with it. Que sera sera. Whatever will be will be.

it is your destiny
Darth Vader: It is your destiny.
Image credit:
Doris Day: Que sera sera. Whatever… Image credit:

The sentiment behind que sera sera seems to be in line with one of the golden rules of time travel; that the past cannot be changed.

What has been, has been.

If the past cannot be changed, and the future is set, one might argue what is the point of time travel? Indeed, a philosophical question.

Maybe time travel is just there for the observational voyeuristic element.

That would certainly account for the lack of time travellers seen wandering amongst our hours and minutes of the present…although the Star Trek “Prime Directive” which nuttles down to respecting non-interaction between those who can and can’t, rears the silent head of a big brother who’s watching over us.

But would observation be good enough? Why travel through time when all we can do is hear and see but not do anything? What good is waking up and smelling the coffee if we can’t take a swig and truly experience the taste of it?

Then again, Luke Skywalker didn’t follow the destiny as described by Vader, did he?

Maybe we can control the future, even without a time machine.

Just wondering…


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