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A Taxonomy of Time Travel

By Steven Lloyd Wilson | Think Pieces | August 31, 2012 | Comments ()


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Scientists at CERN either made a mistake a few weeks ago in extremely complex calculations involving probability distributions, neutrinos, particle accelerators and other timey-whimey stuff, or they inadvertantly managed to make particles go faster than the speed of light. And as anyone who has studied relativity can attest, the equations say that means that stuff went back in time. It's a neat result of the equations really, in which you notice that the term that calculates time dilation goes negative if you plug in a velocity greater than the speed of light. Of course, what's easy to point out in an equation is a bit of a challenge in real life, what with it hypothetically taking infinite energy to accelerate anything with mass to that impossible speed limit. But even before Einstein's work opened up the theoretical possibility of time travel, it's been a fascination of fiction.

The problem is that while time travel is an inherently fascinating component of a story, it is also a complex enough phenomenon that it often fails to retain any sort of logical consistency, falling apart upon closer examination. Time travel in fiction thus falls into a few loose categories. It's unclear yet whether it does in non-fiction, but I'll let you know if CERN gives us any updates.

There is of course what is simplest to dub as time travel for idiots. Back to the Future is a perfect example, and one painful to accuse given that as a fun story it just works so well. But it fundamentally cannot get a handle on the notion that cause and effect happen in a certain order. Go back, make a change, return to find the world different. It seems basically right except for two trip-ups. The fading photograph (and eventually fading Marty) is the worst offender that makes for a clever story mechanism but breaks temporal logic. Setting aside all of the other clutter and contradiction consider it in its simplest terms. The photograph taken back in time now exists before it was taken. Changing circumstances such that the photograph was not taken cannot change the photograph because that would make an effect appear before the cause.

Then there is time travel that works on a slightly smarter level, by at least appreciating the consistency of cause and effect. These are the most common stories: go back, change something, return to find the world different. I read a short story once that operated on this principle and proposed that the greatest crime was changing the past, because while you might have saved six million by killing Hitler as a baby, you murdered an infinite number of lives in the destroyed time line. But this of course sets up the paradox. If you go back in time and create a world in which you were never born, how do you exist? A paradox, you suggest? These stories are just smart enough to understand that effect must follow cause, but are not quite able to work out the math to a proper result. We'll return to this in a moment.

As a slight aside at this point, we should bring the many worlds hypothesis into play. The many worlds hypothesis is a loophole sometimes used to make the logical problems with the above setups resolve themselves. It posits that for every possible event, the universe branches into multiple universes, creating an infinite number of universes in which every thing that ever could happen, did happen. This allows story writers to get away with egregious offenses against the logic of cause and effect by merely waving a magic wand and declaring that the characters are now in a universe in which such and such did or did not happen. Go back in time and kill Hitler as a baby? The reason that you remember a future in which he lived is because you were in one time stream, but now that you changed the past you are in a different parallel stream.

While the many worlds hypothesis has the appeal of at least being logically consistent, it has a glaring problem. It's a brute force hammer of solving the problem, like multiplying by zero to demonstrate both sides of the equation are equal. It's just plain inelegant. But it also has the story flaw of essentially rendering time travel moot. If anything that can happen, has happened in an alternate timeline, then the actions of the characters do not matter one bit. Going back in time and killing Hitler as a baby doesn't change anything, because there is still an original timeline in which he doesn't die.

The gold standard of time travel stories is the construction of a four-dimensional knot. They are relatively rare, with Heinlein's All You Zombies taking the ultimate prize, and various "Twilight Zone" episodes sneaking into that territory as well. "Futurama" has also pulled it off multiple times. The key is in realizing that while it is possible to go back in time and change the past, there is no apparent change because you are already living in a world with that change as part of its timeline. Want to kill Hitler as a baby? You already failed. It's not that there's a lack of free will, or that changing the past is impossible, it's that you already did it. Or in other words, a proper time travel story has no paradoxes because working the math through, the remainders cancel out.

It is possible to go back in time and become your own grandfather, but only if you accept that you've already done so. Tying a knot in three dimensions is incomprehensible in two dimensions, the end result is an impossible construction when viewed by someone in a two-dimensional world. What we see as paradoxes in time travel are the knot in four dimensions.

Steven Lloyd Wilson is a hopeless romantic and the last scion of Norse warriors and the forbidden elder gods. His novel, ramblings, and assorted fictions coalesce at www.burningviolin.com. You can email him here.



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  • luckypete

    12 Monkeys is a perfect movie example of the (gold standard) four-dimensional knot. He's sent back in time to stop the problem, only to learn that he's already done it before, and as a kid there in the same place as his adult self, he witnesses something that he will inevitably do in the future (and the cycle repeats ad nauseum).

  • ,

    OK, so which movie does time travel the best and most logically?

    I see a vote for "Primer" down below. Does, say, "Memento" count?

  • ,

    "It is possible to go back in time and become your own grandfather"
    ---
    Oh, it's not all THAT hard, really:

    Now many many years ago when I was twenty-three
    I was married to a widow who was pretty as can be
    This widow had a grown-up daughter who had hair of red
    My father fell in love with her and soon they too were wed

    This made my dad my son-in-law and changed my very life
    My daughter was my mother 'cause she was my father's wife
    To complicate the matter even though it brought me joy
    I soon became the father of a bouncing baby boy

    My little baby then became a brother-in-law to Dad
    And so became my uncle, though it made me very sad
    For if he was my uncle, then that also made him br'ther
    Of the widow's grown-up daughter who was also my stepmother

    Father's wife then had a son who kept them on the run
    And he became my grandchild, for he was my daughter's son
    My wife is now my mother's mother and it makes me blue
    Because altho' she is my wife, she's my grandmother too

    Now if my wife is my grandmother, then I'm her grandchild
    And every time I think of it, it nearly drives me wild
    For now I have become the strangest case I ever saw
    As husband of my grandmother, I am my own grandpa

  • GunNut2600

    In my view, there are two basic thoughts of time travel, ultimately leading to the conclusion that it is pointless to even try.

    There is the Greek concept that effectively means that everyone is subject to fate. Merely knowing your future damns you to do what is predicted. We see this over and over again in Greek Mythology.

    The other side of the coin is that the future is fluid. Any knowledge gained from seeing the future leads to the future changing in any unpredictable manner. This ultimately makes knowing the future pointless. Sort of where you could imagine Romney having a time machine and the future says he is going to win. But since he knows he is going to win, he doesn't try as hard, ultimately violating the conditions where he would win, leading to him not winning.

    I don't believe in fate, therefore I lean to the second scenario. But again, even if I had a time machine, it would be worthless. Actually, it would be worse than worthless as just imagine time terrorism. That would actually be an interesting concept to me. Imagine what the crazies would try to do to put themselves on top.

  • L.O.V.E.

    (Takes a bong rip)

    Duuuude. Exactly.

    (Takes another bong rip)

    But what if Bruce Willis is me, living my life as a future me, but only after coming back from the future to kill me? No, no. Wait. What if I came back from the future to kill Bruce?

    (Takes another bong rip)

    So is that (takes another bong rip) murder? Or, like, suicide?

    Ahhh shit. I just blew my mind.

  • Samantha

    ...Way to ruin Back to the Future for me.

    I've always used the Twilight Zone where they go back to kill the Hitler baby as an example of this (they killed the official son, but then the nanny replaced him with another child who grew up to be the Hitler that we all know and love).

  • Gaby

    Loved it! More, please.

  • The Heretic

    No mention of Primer, the greatest time travel film of the 21st century? Pajiba... SON, I am disappoint.

  • Wōđanaz Óðinn

    Beat me to it.

  • lowercase_ryan

    Fuck yeah Science! The fact that I understood this makes me think I need to go back and watch Primer again.

  • Bert_McGurt

    As far as I understand it (which is not to say I understand it correctly), particles can be moving at a speed faster than light, so long as they don't accelerate to get there. Not that that really has anything to do with the rest of the article.

  • Snath

    My brain hurts, but this is brilliant.

  • Romeo Cranberry

    what the fuck wilson? was there a coup at pajiba? did you murder rowles and take over as pajiba overlord?

  • ReturnofSantitas

    Haha, I had the same thought, having also missed Dustin's earlier post. Hell, it had a volleyball on it, so I ignored it. Who wants to read something about a volleyball?

  • Snath

    You obviously missed Dustin's post earlier today.

  • Sara S.

    Pajiba's teaching me all sorts of stuff today! Again, lots of new tidbits I can quote to delight my nerdier friends and annoy my less-caring pals.

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