In Predestination starring Ethan Hawke, the idea is plain and simple. However, I do find something very hard to digest:

How could the loop about Ethan Hawke the time travel agent, could meet himself and then conceive himself without some sort of help to initialize the loop?

What I want to say is that, in the first loop of the story, there is only one Ethan Hawke. He then travels back in time and after meeting his past self, he gives birth to himself. But who was responsible for the birth of the first Ethan Hawke?

As a developer this bugs me more than it should. Any theories?

  • 3
    Closed timelike curves violate causality, which is why we physicists don't believe they exist outside Sci-Fi. Jan 9, 2015 at 9:33
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    @user14111 - Agreed. Since time travel is, at least theoretically possible, there can't simply be "a rule against them". There has to be a hard and fast scientific reason why you cant have them.
    – Valorum
    Jan 9, 2015 at 11:09
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    This is known as the bootstap paradox. Jan 9, 2015 at 18:23
  • 2
    Alas, the plot isn't original. "Terminator" had John Connor's father be the soldier John Connor sent back in time to prevent the assassination of Sarah Conner, his mother, by the T-100, sent back by Skynet to ensure the machines won by killing John Conner...
    – phyrfox
    Jan 9, 2015 at 18:55
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    @phyrfox of course the plot isn't original, it is film adaptation of a Heinlein short story from 1959.
    – Zoredache
    Jan 9, 2015 at 21:51

8 Answers 8


This movie, along with the original "All You Zombies" story that inspired it, seems to be one that assumes a fixed unchangeable timeline, one obeying the Novikov self-consistency principle. In this type of story there is no "original" version of events that "initializes" an altered timeline, instead there is just a single timeline which is constrained to be totally self-consistent.

Since you mention you're a software developer, it might help to think of this sort of thing in terms of how we might, in principle, create a computer simulation of a world where time loops of this kind can occur. To start, imagine you want to write a computer program to generate a possible chess game. One way is to start with the pieces in their initial configuration, then have the program generate each successive configuration on the next turn from the configuration on the previous turn, using only legal chess moves. But here's another, more elaborate way to do it. Imagine we just program the computer generate an entire series of configurations at once, completely randomly, so it just picks randomly which pieces to put in which positions on which turn. It is very unlikely that the resulting series will look like a legal chess game--a piece might randomly be on a particular square on one turn, but then the next turn randomly be on some totally different square that it shouldn't be able to get to in one move by the rules of chess. But suppose as a thought-experiment that you have access to an idealized computer with nearly infinite speed and memory, and you have it generate a gigantic number of random series this way--if your number is large enough, chances are at least some of the series would just happen to satisfy the rules of a legal chess game. So you could specify that the computer should throw out all series which violate the rules of chess, and be left only with series that represent legal chess games. But since you are dealing with an entire series at once, you could also place other constraints on them, like "throw out all series where white wins", or "show me only series where the black rook checkmates the king in 25 moves", whatever you want. For sufficiently detailed conditions, it might be very hard to generate a chess game that matched them in the traditional way of starting from the beginning and basing each new configuration of pieces on the configuration of the previous turn, but using this brute-force method of generating a near-infinite number of entire histories, and throwing out all but the ones that satisfy your constraints, it's easy to get a game that satisfies any conditions you like without even having to think about it or plan the details of the game.

And suppose we want to come up with a game of "4D chess" which is similar to ordinary chess but with some extra rules that allow you to send pieces "back in time" to earlier turns in the game, but only in a self-consistent way where history is not changed. For example, suppose there are two squares labeled A and B on the middle of the board, such that if on any turn a piece is moved onto square A, then the rules say it is transported to square B four turns earlier (and say the player who controls the piece has to immediately move it when it appears on square B, and pieces can't move directly to square B by non-time-travel routes, to avoid the issue of multiple pieces occupying square B on a particular time-increment). It would be pretty hard to generate self-consistent games following these rules by the usual method of starting from some initial configuration and evolving it forward step-by-step, but if you just generate some astronomical number of random histories, the computer can algorithmically check any given randomly-generated history to see if it actually is a self-consistent 4D chess game that obeys the rules at every point, so with enough memory and computing power it should be able to find some valid games.

You could do the same thing with other simple types of "games" where there are rules governing how the configuration on each time-step must be related to the configuration on the previous step, like a cellular automaton. For instance, you could use this sort of method to generate a time-evolution for something like the Game of Life, but with a "wormhole" somewhere on the board where the state of the cells at a particular location at one time-step would be defined as "neighbors" for some cells at a different location at an earlier time-step, so that mobile patterns of cells like gliders might be able to enter the "wormhole" region at a later time and exit at an earlier time, perhaps even going on to interact with some other pattern of cells in a way that would lead to the creation of the same glider that would later enter the wormhole, like a small-scale version of the life story of the character in Predestination.

We could make this even more grandiose, and imagine using this incredibly powerful computer to generate a simulation of an entire universe obeying some set of fundamental "laws of physics"--instead of picking some initial conditions and then letting it evolve forward according to some set of laws of physics, you could again specify your "laws" in terms of constraints on entire histories, with the computer generating a huge number of random histories and then throwing out all the ones that don't satisfy the conditions. If the "laws of physics" you pick happen to allow time travel, then obviously any universe that respects the laws of physics locally at every point in spacetime must be globally self-consistent, and the computer will find some histories satisfying this condition. But the computer does not need to have any intelligence to do this, it isn't playing the role of a sentient "Fate"-like force, it's just randomly generating a huge number of possibilities until it finds one that satisfies the constraints. From the point of view of a simulated sentient being in this universe with access to a time machine, it might seem like the universe was cleverly finding ways to "outsmart" them and thwart their plans every time they tried to change history, but it would actually be the result of a fairly simple rule, just not a dynamical rule based on picking initial conditions and evolving them forward, as with normal computer simulations.

Of course, this is assuming that the behavior of intelligent beings can in principle be explained in some type of reductionist way, as the emergent outcome of huge numbers of fundamental particles (or whatever the most basic physical 'unit' is) in some configuration, with their collective behavior following from their arrangement at each time along with the fundamental laws of physics governing how they interact and move over time. If intelligent beings have some sort of mysterious libertarian free will (as opposed to compatibilist free will), then you might say that while this method could generate self-consistent time loops involving inanimate objects (like the ones involving billiard balls that I discussed in this answer), it wouldn't generate any involving intelligent beings like the one involving the characters in Predestination. But I think most physicists (not to mention A.I. researchers) would favor the idea that all physical behavior, including that of intelligent beings, can always in principle be explained in terms of a collection of fundamental units obeying mathematical laws.

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    This is by far, the most complete answer to my question. I not only enjoyed reading it, I actually really appreaciated the examples breaking down the complicated theoretical answer. Thank you sir, you deserve more than one upvote. Jan 11, 2015 at 16:41
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    This answer is so good and well thought out it deserves a thousand upvotes.
    – Andres F.
    Feb 2, 2015 at 16:19
  • Hypnosifl - have you seen the movie Mr Nobody? I think you might enjoy it.
    – Wudang
    Sep 15, 2016 at 16:35

That's the whole point of it being a paradox. It is paradoxical.

Adjective : Seemingly self-contradictory

One of the main elements (arguably the main element) of the film is that we're observing a closed loop from the inside. As such, the first Ethan Hawke was his own prime mover, recursively. There's no need for a first cause inside a temporal loop since each effect is both preceded and followed by its own cause, bootstrap style

Since time travel is a fictional construct (at least as yet), my advice is to follow to MST3K Mantra;

Repeat to yourself "It's just a show, I should really just relax"

  • Indeed. From a dramatic perspective, I prefer closed/paradoxical loops. I don't need them to make scientific sense, because it makes dramatic sense. As Phil Dick says re: his time travel story, "A Little Something for Us Tempunauts": "The essence of the time-travel story is a confrontation of some sort, best of all by the person with himself. Really, this is the drama of much good fiction anyhow, except that in such a story [...] the moment in which the man meets himself face-to-face permits an alienation that could not occur in any other variety of writing."
    – Andres F.
    Jan 9, 2015 at 14:06
  • Technically the loop could both be a paradox and have an initial event that set it off and closed the loop. Jan 9, 2015 at 18:27
  • I digress but one could engineer a person with the capacity to reproduce themselves and then introduce them into a loop. Jan 9, 2015 at 18:34
  • @MarkRogers - Ah, but you can't create a temporal loop from the outside unless you have some way to isolate yourself from the paradox you've just created.
    – Valorum
    Feb 6, 2015 at 13:50
  • @Richard - I was going to ramble on about clones, but I guess it all depends on the model of time-travel. Feb 6, 2015 at 15:22

It doesn't "get initialised". That's the entire point of the whole thing.
It is a predestination paradox (hence the title of the movie).

  • 1
    Thank you for this answer, it guided me indeed in the right direction. I looked the predestination paradox up and found another paradox imbedded within which answers exactly my question: the bootstrap paradox Jan 9, 2015 at 14:28

You are thinking of time as linear - an event must occur before the next event (cause and effect), etc.

In the film's mode of thinking, however, time is actually a dimension. In that sense, it all exists simultaneously, so there's no "before" or "after" - the "changes" we see are merely changes in our perception - not of reality itself.

Imagine a 3D cone shape passing through a 2 dimensional plane. The 2D creatures inhabiting that plane would first see a dot, then a steadily growing circle, then it would disappear entirely. These 2D creatures would tell you that the shape clearly changed, but actually it was their perception that changed. They could only see a single 2D "slice" at any given time. In actuality, the shape was complete and whole all along and did not change.

The "4D" time theory suggests time is the same. As 3D creatures, we perceive a change from one moment to the next, but actually all of time exists simultaneously and in its complete state.

There are, of course, many other theories of time and I don't personally subscribe to this one, but it does help to solve these kinds of "paradoxes".

  • +1 for this. At least in fiction the entire history of the universe "just exists" as an object. Adjacent bits of it are related by the laws of physics, fine, but there's no particular reason (again, in fiction) to prefer universal histories with no loops, to universal histories with loops. Physicists have their arguments on the subject, of course. ISTR Hawking at one point was very much looking for mathematics that would permit loops while offering an explicit mechanism to forbid impossible "self-contradictory" loops. Jan 9, 2015 at 22:58
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    Analogy: draw the Feynman diagram of an electron-positron pair appearing out of the void and then shortly afterwards mutually annihilating. As far as the diagram is concerned a positron is just an electron travelling backwards in time, so what you've drawn is just an electron that exists for no particular reason in a certain region of spacetime, tracing a circuit. Physicists offer subtle explanations why this isn't the same as Ethan Hawke being his own father, but I say again, good enough for fiction. Jan 9, 2015 at 23:01

Like most time travel paradoxes in fiction, they are initialized by the author of the screenplay.

An actual predestination paradox would require either that

  1. the characters have no free will (i.e., they are helpless to do anything other than fulfilling their own destiny, either through ignorance or an external force of Fate controlling their actions or circumstances), or
  2. the result of the paradox is something desirable that, even with free will, the character chooses to carry out (e.g., the character in "Predestination" learns that he was born only as a result of the paradox, so he makes a point of sustaining the paradox to ensure that he will have been born).

This movie seems to be a combination of the two, with the younger character being ignorant of the paradox, and the older character actively perpetuating the paradox.

The problem is that the characters in this movie work for a time travel agency unrelated to the paradox. Presumably the function of time cops is to go back in time and alter the past, or prevent the past from being altered. But in a story primarily about a predestination causality loop, the existence of other time travelers actively trying to change history seems incongruous with the premise of the paradox. How can the same time machine be used both to change history, and at the same time perpetuate a self-recursive predestination paradox?

(Or, if every use of the time machine results in a predestination paradox, how long would it take the time cops to realize that they are completely ineffectual, going back in time only to do what was already done in the first place? Like Skynet causing the existence of John Connor by trying to prevent his existence in the first "Terminator.")

The movie also doesn't address what would happen if the character did have free will and chose not to continue the causality loop after becoming aware of it (e.g., what if he killed his younger self instead of his older self? With one decision, he could have gone from a predestination paradox to a grandfather paradox.).

  • "if every use of the time machine results in a predestination paradox, how long would it take the time cops to realize that they are completely ineffectual": how long? Every person only lives once. They don't have multiple lives to experiment with every choice. They never get any wiser: each person goes through the loop completely fresh. What you say would require temporal agents going through the experience more than once, which doesn't happen.
    – Andres F.
    Feb 2, 2015 at 16:43
  • "what would happen if the character did have free will and chose not to continue the causality loop after becoming aware of it": that's the beauty of the closed loop. Whatever the character 'chooses' to do, it's what he actually did in the past :) Trying to escape the closed loop only fulfills it. It's not merely a sort of Fate: what is happening already happened; you cannot do anything else, else you wouldn't be there in the first place!
    – Andres F.
    Feb 2, 2015 at 16:45

The predestination time-loop doesn't get initialized. It was just "meant to happen" and it exists through Novikov self-consistency principle.

Did universe had initialization? No, it just exists. Of course there was big bang, but there was no entity needed to start it whatsoever.

This scientific theory was used in many other sci-fi stories, e.g. Doctor Who.


Regarding other answers here:

Predestination is is not a paradox! Check this discussion below:



He went back to trigger it all, which means in the beginning when there is just Ethan Hawke, as you say, the beginning of the loop was his past, which he couldn't change. The decisions he makes in his time line, have already been made by him in the loop. He just doesn't realize that till the point comes in his current "line of time" to make that sort of decision. Just like at the end of the movie where he finishes the loop by killing his older self. His older self knew(?) what was about to happen, but couldn't stop as it was all "predestined".

  • Does this truly answer the question? The OP seems to be asking how a closed loop is even possible.
    – Andres F.
    Jan 9, 2015 at 14:09
  • My answer is for the part of the question where he asks "who was responsible for the birth of the first Etahn Hawke?" I don't think closed loops are possible, but in the movie universe, that's how I get it.
    – Veda
    Jan 11, 2015 at 11:37

May it this is a side explanation but here is it.

As being of 3 dimensions, we cannot understand matters occurring in the 4th dimension (Time). We are typically going forward in time in a linear way. But if we try to go in a different direction in the 4th dimension (time) , things get complicated.

We do not grasp all the parameters of that dimension to correctly model the universe (genrate space from Basis vector). It have taken an Einstein to discover that time is the 4th dimension and we need to think in time and space simultaneously, maybe there are other dimension that we have no idea about.

In conclusion, the answer here is we lack some parameters in our model of the universe to fully understand the initialization phase.

  • The concept of time being a "4th dimension" predates Einstein by 200+ years. Lagrange and Mobius were talking about this in the 17 and 1800s and it wasn't a new idea even then.
    – Valorum
    Jan 9, 2015 at 16:49
  • Time isn't a spatial dimension in the way that up, down, left right and depth are, so it's misleading at best to label it the fourth dimension. Time is a property of space and is a dimension, but not a spatial one. Feb 18, 2015 at 11:37

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