Talk at the OUSFG Discussion Meeting of 30th October 2002.

Tomorrow's Talk: Time Travel

Before I start, I want to make it clear that this is a discussion and not a speaker meeting. I will be disappointed if someone doesn't interrupt me to disagree with what I say. Please don't be intimidated by my Doctorate in High Energy Physics, nor the fact that I am one of the discoverers of the largest observed violation of time-reversal invariance. Just because I've built my own time machine in my attic, you shouldn't be shy about interrupting me and telling me I'm talking bollocks.

As an aside, let me tell you how useful a time machine is. Since I didn't get this talk written in time, I checked the attic, and there was the completed talk sitting in the time machine. Tomorrow, I'll send the talk back to yesterday, allowing me to completely skip writing it. The clever bit, is that I generated a talk out of a paradox without ever having to write a word. It's even just what I would have written if I could be arsed.

I'll start off by making a few general and controversial statements. It's then up to you to disagree with me. Even more importantly, I hope you'll have plenty of stories to retell, because (and here comes controversial statement number 1) Time Travel stories, probably more than those of any other subgenre, are all about plot. Characterization, literary merit, and extrapolation of technology or society, are all secondary to the 4-dimensional twists of the plot. Maybe this explains why many of the best Time Travel stories are short stories.

Controversial statement number 2: a time travel story isn't really a time travel store unless it involves travel into the past. We all travel forward in time at a rate of 24 hours every day, and there's nothing really special about speeding up that rate. Whenever you fall asleep, perhaps. You can achieve a longer leap forward with cryonic suspension, such as in the film, Forever Young, where Mel Gibson, frozen in 1939, is accidentally resuscitated in 1992 and has to learn about answerphones. As a decent chap, as of course everyone was in 1939, Jamie Lee Curtis falls for him, and it all gets very soppy, so I'll leave it there.

If you want to get really ambitious, you can use the time dilation effect, either by travelling close to the speed of light, or passing through an intense gravitational field, such as close to a black hole. This is used to great effect in Joe Haldeman's The Forever War, where the dislocation felt by soldiers returning to earth centuries after they left is used as an allegory for the dislocation felt by returning Vietnam veterans.

Poul Anderson's Tau Zero takes this to extremes: after an accident, a spaceship is forced to accelerate continuously, allowing it to outlive the Big Crunch and another Big Bang.

But none of these are proper Time Travel stories. Jumping into the future offers a convenient mechanism for the protagonist to see what that future might be like (and that can be very interesting in itself), but gives no scope for doing anything unusual with Time, and critically, has no possibility for paradox. Embarrassingly, my stipulation that a Time Travel story requires travel into the past, disqualifies the seminal and probably most famous so-called "Time Travel" story of all. In H.G. Wells' The Time Machine, the Traveller does eventually go back in time when he returns to the present, but this is a postscript to the main story, which involves Wells' ideas on the evolution of humanity and human society.

Since we're always trying to encourage people to write for Sfinx, I'll now tell you how to write a Time Travel story.

You need a mechanism to travel back in time

In principle this is your biggest problem, but do not despair. Although most physicists will tell you that Time Travel is impossible, physics gives plenty of loopholes and buzzwords to choose from. Here are a few.
  1. All you need to do is travel faster than the speed of light. Then you arrange for your superluminal device to transport you between a rapidly-moving spaceship and the earth, and bob's your uncle, you'll return from your jaunt before you set out. Tachyon is a good buzzword to use at this point (all it means is a superluminal particle).
  2. If you think your reader too smart for that one, you can always arrange to fall into a black hole. Since no one really knows what happens then, particularly if there's a singularity involved, you can have the laws of physics break down in any way you like. The problem, of course, is that you'd probably be converted to neutronium by the tidal forces on your way in, unless you found a really big black hole to play with. I'm sure I left one around here somewhere.
  3. This is all ignoring the gravitational physicists who keep coming out with papers suggesting ways you really could travel round a closed causal spacetime path (that's General Relativity-speak for returning to where and when you started). Sadly, the engineering requirements are a little extreme such as structures weighing more than the rest of the Universe. Still, if you like technobabble, there are plenty of buzzwords to play with: closed causal spacetime path, negative energy, and time-reversal invariance violation. I really did measure that last one (actually the related effect of CP violation). Although it sounds good, it unfortunately doesn't help in building a time machine. You don't have to tell your readers that, though.
  4. If all else fails, you can always use the mad scientist or magician dabbling in forces that no mere mortal (protagonist included) can understand. The Anubis Gates by Tim Powers is a good example of this. This is an excellent fantasy novel, that mixes in elements of horror, mystery, historical romance, as well as time-travel paradox. In a wonderfully convoluted plot, our hero meets Old Kingdom Egyptian sorcerers, romantic poets, a werewolf, secret societies, grotesques inhabiting the London sewers, and of course himself.

You need a theory of time

Unless you are going to be very circumspect, you need to decide what happens if you go back in time and try to kill your mother as a child (the more traditional grandfather isn't such a problem given the difficulty proving paternity). Herein lies much of the fun.
  1. Just can't be done. You seek out your mother, but she's in hiding. You murder the little girl, and as you mount the gallows you see her identical twin watching you. Just as you cock the pistol, a meteorite strikes you down. Whatever you do, History (with a capital H) conspires against you.
  2. A variation on this theme is The end of the Universe. A paradox would cause the universe to be destroyed. This thesis is carefully and thoughtfully examined in the Back to the Future films.
  3. Fixed past. Perhaps one can travel backwards in time, but can't change anything at all. One is entirely an observer, unable to move a blade of grass (eg. An Age by Brian Aldiss, who'll be visiting us in 6th Week).
  4. Alternate worlds. When you kill your mother, a parallel world where you never lived is created (or revealed). Don't get me started on Alternate worlds, or I'll start talking about Quantum Mechanics and how it proves that I am immortal.
  5. The Time Police prevent you. Silly idea.
  6. Although not much use for Time Travel stories, Larry Niven has made an interesting argument. Suppose that Time Travel were possible, with a single, malleable, timeline. This is an inherently unstable situation. As long as people go back in time and change the past, they will inevitably affect themselves, even if only slightly. These small changes are cumulative - eventually a timeline will come about where that person never invented the time machine, or didn't use it. This is the only stable state: where no one ever used a time machine. Since systems tend to evolve towards a stable state, this has probably happened. Ie. Time Travel is possible, but never practiced.
Whatever your theory of time, the important thing is to be consistent. There's nothing more annoying to a reader than a gaping inconsistency, when the logical puzzle is much of the fun that a time travel story allows.

At this point, let me recommend two Heinlein shorts, All You Zombies... and By His Bootstraps, which are classic paradox puzzles.

The Plot

If your hero manages to avoid a paradox, then there's all the fun of twisting fate. What would happen if you inoculated the Central Americans against European diseases before Columbus's arrival? Orson Scott Card's Pastwatch - The Redemption of Christopher Columbus has a future society altering history in an attempt to bring about an enlightened present.

Could one fix up all one's past misfortunes and lead the perfect life? Oddly, this always seems to lead to one being the instrument of one's own misfortune.

How would you recognise other Time Travellers without alerting everyone else? Ken Grimwood's fantasy, Replay, is an entertaining example.

I'll gladly tell you more about any of the stories I've mentioned (and could bore you with many more), but it's your turn now.

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