Theories of Time Travel

Last week I explained the inexplicable nature of time, and demonstrably proved that time travel is impossible. But speculative fiction was never known to follow the rules, and steampunk, specializes in the impossible, so who’s going to let a little thing like physics stop them? Not me!

Once you’ve got your time machine working (and found the infinite energy source that’s going to power it) you have to decide: will you travel into the future or into the past? If you’re going into the future then all we have to say is good luck, enjoy the flying cars, and “you realize that cryogenics can do the same thing, right?” Travelling into the future is easy. We all do that every single day. It’s going into the past that’s hard, and if you’re going to blaze that trail there’s a few things you should be aware of first.


Parallel Universes

Examples: Timeline, Star Trek (2009),

Technically, parallel universes don’t count. In this example you are not travelling through time, but across time streams. So instead of going into your own past, you are going into the past of an alternate version of you. Thus you can return to your own time stream without repercussion. Or, alternately, when you go into the past and muck things up and return to the present you aren’t returning to your own present, you’re returning to the parallel world that was created when you went back in time in the first place.

This basically solves the Grandfather Paradox, because if you go back in time and kill your grandfather you were never born, but you don’t blink out of existence, because you’re not from this timeline, so there is no conflict. This is the most plausible theory of time travel because it’s grounded in string theory, and was ostensibly the version used in Timeline, although in practice it played out more along the lines of the Predestination Timeline.

Doctor Who TV series starring Christopher Eccleston, David Tennant, Matt Smith, Billie Piper, Karen Gillan, Freema Agyeman, Catherine Tate, Alex Kingston, Jenna Coleman, Paul Kasey, Nicholas Briggs, Arthur Darvill, Noel Clarke, John Barrowman -

“History says a bomb went off here. Who am I to argue with history?”

Resilient Time

Examples: Doctor Who, A Connecticut Yankee in King Arthur’s Court,

Resilient time is time that heals itself. History is going to take the course that history is going to take, and a few time travellers here and there are insignificant. You might throw a stone and make a few waves, but those waves will smooth out, and the march of history will continue unabated. You might try to go back in time to kill Hitler, for example, but discover it’s not as easy as you thought it would be. Or maybe you do kill him, and then two years later someone else comes along who accomplished basically the same thing, and after about a decade there’s really no noticeable difference in the progress of civilization. You won’t create a paradox in fluid time because either you’re prohibited from crossing your own time stream, or visiting the near future, or you’re not stupid enough to make such an attempt. Thus your own existence is assured, and you can have fun bouncing around the time stream without causing the universe to have an existential crisis.


Fluid Time

Examples: Back to the Future, Timebound, Ocean of Time, Star Trek.

Fluid time is exactly what everyone who worries about time travel thinks it is. If you go back in time and prevent your parents from ever meeting, boom. You cease to exist. Prevent WWI and come home to find a Canadian flag hanging on your wall. Anything is possible, and it can get very messy, very fast. It’s also the most high-stakes version of time travel, especially if you’re fighting a war. (Here are some recommendations for this kind of time travel!)


Predestination Timeline

Examples: Timeline, Harry Potter, SG-1: 1969.

So this example of time travel is the most rigid of all. You can’t create a paradox. You can’t interfere with history. You can’t step one foot off the path that you were destined to follow from the beginning. You’re not going to do anything different than what history dictates, because you were there when history was written in the first place. Time, in other words, is written chronologically. How you experience it is your own business entirely. You may attempt to thwart the past version of your future self, but ultimately you will fail. You can’t screw anything up because you’re just experiencing something that already happened.

This often leads to the bootstrap paradox. (Doctor Who: Before the Flood, Doctor Who: Blink.) The bootstrap paradox is what happens when a time traveller acts upon information given to him by his future self, leading to the creation of that exact future self to pass the information back to his past self. The information itself is never created, for it always existed. The path followed by the time traveller is remarkably circular. Crucial information can be placed in the most unlikely of places by the future self in the past, to be discovered by his past self in the present. Michael Crichton’s great novel Timeline is set both in 14th century France and in the present day; as the time travellers begin uncovering evidence of their adventures that have not yet taken place, eventually enabling communications across the decades in the form of notes hastily written and left in a basement to be discovered six centuries later. The time travellers in the past could leave those notes, knowing they would be discovered, because their past selves had already discovered them in the present.

This form of time travel is very similar to the self-fulfilling prophecy, and precludes any notion of free-will. Time travel written in this theory of the universe can be exhilarating to unravel as the plot unfolds, and also lead to interesting existential discussions, while ultimately causing no harm to the fabric of space-time, and reintroducing a little bit of mystery into a world made plain and sterile by science.


Katie Lynn Daniels is the author of Supervillain of the Day, and the mastermind behind Vaguely Circular. She blogs about science and things that are peripherally related to science. You can read all her posts here.


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