A Matter of Time
Written by Denis Faye

(February 26, 2013) 


Or should I say… when to look? Ah, time travel humor. It never gets old, does it? That’s why you’ll suffer no shortage of writing on the topic.  

First, there’s the fiction. According to Huggett, Robert A. Heinlein’s short story All You Zombies is a must-read. You can download it for five bits from Amazon. Carl Sagan’s fictional adventure, Contact, is also filled with enlightened ponderings on the topic. 

On the practical side of things, your first stop might be this article from Steven Hawking, “How to Build a Time Machine.” Then to get more in-depth, you can read the book with the same name written by Paul Davies. There’s also the redundantly titled Time Travel in Einstein’s Universe: The Physical Possibilities of Travel Through Time by J. Richard Gott. 

Kip S. Thorne’s Black Holes and Time Warps; Einstein’s Outrageous Legacy contains some interesting thoughts on time travel, as does Nick’s book, Everywhere and Everywhen.  

Finally, writing about time travel can be draining on the cranium, to say the least, so plenty of downtime will be a necessity. When you’re procrastinating on the Internet, as you will be, make sure to do a little time traveling yourself using the Internet Archive’s Wayback Machine. What did Facebook look like in 2006? You now have that ultra-important information at your fingertips, no wormhole required. 

If you want to talk to an expert about time travel, you have three choices. Either seek out a professor of physics, a professor of philosophy, or someone from the future who has experienced the phenomenon firsthand.

Obviously, my first choice was to speak with a real, living time traveler, so I approached this guy who spends a lot of time hanging out in front of my local Trader Joe’s and claims to be from the year 3215. Unfortunately, it was hard getting him to focus and his mylar suit interfered with my digital recorder, so instead I went with plan B, a philosophy professor.

And I’m glad I did. University of Illinois, Chicago Professor Nick Huggett is one of those talented souls with the ability to make complex subject both graspable and fun, as evidenced by the interview below, not to mention his book Everywhere and Everywhen, a primer on the philosophy of physics.

With that in mind, this month’s Technically Speaking might be, in the words of Dr. Who, a little more “wibbly wobbly, timey wimey” than usual. Don’t panic, just make sure to get the speedometer up to 88; don’t forget your towel; and, above all, be excellent to each other.

Let’s start with the world's most obvious question about time travel. Is it possible?  

There are two ways of taking that question. One is whether it's compatible with what we know about physics today and the other is just whether it's logically possible.

People have done some work on whether it's compatible with physics and there seems to be a certain sense in which it is compatible with physics. There are ways that you could actually construct loops in space and time between the past and the future. As for the logic question, most philosophers think that it's logically possible, despite worries about grandfather paradoxes. Would you like me to talk a bit about that? If time travel is possible, can you go back and change the past and prevent yourself from being born?

Sure, absolutely. That's what Back to the Future [Written by Robert Zemeckis and Bob Gale] is based around.  

Right, right. I guess there are two kinds of approaches to that. One is the approach that you get in Back to the Future and I guess quite a lot of other movies take this approach as well. I can think of many episodes of Star Trek where the same thing happens and you resort to multiple time lines in some way.

So when philosophers have thought about it, they've addressed the question about whether time travel is possible without having to invoke multiple timelines. So back in the 1970s a philosopher from Princeton, David Lewis, wrote a very nice paper discussing these situations where he really made the very simple observation that when we say things are possible we can mean that in different senses. So the example he gave was, I think, speaking Finnish. He said it was possible for him to speak Finnish in the sense that he had a normal human voice box and throat, and he was capable of making the normal range of human sounds, but on the other hand he'd never studied it so it also wasn't possible. So his point was there's no paradox here between saying it's possible for me to kill my grandfather, and it's not possible to kill my grandfather because we mean different things.


You see, when philosophers watch time travel movies, what they really are looking for is a consistent time travel story. You can see it's going to be hard to tell a clever story that way because the facts of the past have to be respected and kept in place, so in a certain sense it's always going to be part of the premise that you know what's going to happen in the past. The person travels back to the past and somehow the suspense has got to be maintained. So there has to be something you're not aware of to maintain it. That's very uncommon so there aren’t that many movies which actually go for that sort of approach. I think the most recent one I've seen is Harry Potter and the Prisoner of Azkaban [Screenplay by Steve Kloves]. I've seen that a couple of times and as far as I can tell everything is done consistently. It's done very nicely because you see the things happening once, but then they happen again, seen from a different perspective.

Following that model, when you go back in time, you're just along for the ride.  

I wouldn't say that. They go back in time, and they're doing things, right? They're not just zombies being carried along by things. Time travelers can make a difference to the past, even though they can't change it. How can that be? Well, “make a difference” is ambiguous. I could make my plate dirty, then clean. But that is to change something – fine for plates, but not for the past, for how could yesterday be one way at some time, and then another way at a later time?

But there’s a different way to “make a difference” – make something different from how it would have been otherwise. If I hadn't said this, you wouldn't have recorded it, so I made a difference to your recorder. This kind of “difference making” is possible. Hermione did travel back in time, and she did throw pebbles through Hagrid's window, so she didn't change the past by so doing. On the other hand, if she hadn't time traveled, or hadn't thrown the pebbles, the past would have been different – so her actions made a difference.

The upshot is that you can make the past different from how it would have been, but not from how it was. Once you've said how it was, that's a fixed point.

We are talking about time travel in one linear plane. We're not talking about time travel in the sense that you go back in time, and you do change something, and then you've created an alternate universe, right?  

I'm talking about the single stream, but even if you're thinking about a multiple streams history sort of story, all the pasts and all those streams are all in the past, right?

What about the Star Trek [Written by Roberto Orci & Alex Kurtzman] reboot, where Spock goes back and changes things?  

That was cute. One thing that can happen in time travel movies is you just go back and literally meet yourself, the person with the same personal timeline, but what happened in that Star Trek movie with two time lines, was that they had their own universal time and space, therefore literally two different Spocks, one for each time line. And what's happening is the older Spock actually travels back across to the other timeline and meets the younger but different Spock.

Think of a movie like Bill and Ted’s Excellent Adventure [Written by Chris Matheson & Ed Solomon] where there's just a single timeline and so that is literally their older selves looping back in the same time line. So if you imagine drawing a line, there's a loop in it so they come back and meet themselves. However, in Star Trek, there are two lines and one of them kind of loops over to meet the other.

So here are two different theories on time travel. One is what you were talking about initially, the Harry Potter version where you're not going to change anything and although you're influencing things, your fate has been predetermined. Then there's the Star Trek one where once you go back your fate has been predetermined, but it's a different time line happening. Is that right?  

Something like that, yeah.

Let's get out of the clouds a little bit. What have you seen in time travel movies that’s really right and really wrong?  

One thing I like is when it's a consistent story; they manage to keep tension and make it interesting even though, in a certain sense, you know what's going to happen in the past. I don't like it so much when they jump from timeline to timeline; it's a little hard to see what that actually means, I guess, in trying to imagine somebody traveling. So I can imagine a path in a single space and time that loops back because you don't ever leave it. But how you get from one universe to another, that's never explained very well.

You mean like all the universes in Back to the Future?  

I do love those movies, they're great, but it's never really explained why the photos are fading and so on. You just take it on face [value]. It's fiction so the universe is built that way, and it plays pretty well by its own rules, but in terms of trying to think of a picture that might actually make sense in terms of how we think time and space actually are, it's hard to see how to do that.

The technology of it is always kind of funny. Physicists have done some work so there are some known ways of making time travel happen. So they generally require, kinds of matter or energy that we don't know actually exists in the universe, so they might not be possible.

Then there are the films that don’t mention the technology at all, the Connecticut Yankee in the Court of King Arthur kind of movies. Midnight in Paris [Written by Woody Allen] did this recently in a rather fun way, but then it's not about the time travel. It's just about the change in period, the anachronisms.

What advice would you give to a writer starting a time travel script, in addition to checking consistency and technology?  

That's if you want to make it appealing to philosophers. I don't know about a general audience. I'd like to have more sensible talk about the technology. There are some films where it just gets really crazy, like Déjà Vu [Written by Bill Marsilii & Terry Rossio], the Denzel Washington one. They tried to explain it, and that just made it worse. It was so convoluted and implausible that sometimes it's better to just have the nice, big spinny thing and leave it at that.

When in doubt, have a spinny thing. What about Doctor Who?  

They're never consistent. Their nod to consistency is when they claim there are fixed points in time, things that can never be changed. Although in the recent series they've even been fiddling with those.

What about the argument that if time travel were possible, we’d have met people from the future?  

A plausible response to that is that if time travel is possible, you can't start at an arbitrary point and build a time machine to the back, you have to build both ends of the time tunnel, whatever it is.

What would you like to see in a time travel movie?  

There must be some movies where this happens but actually, I’d like to see them deal more thoroughly with people meeting themselves. Usually people try to hide from themselves, I think because it makes it very hard to keep things consistent. You would be faced with dealing those issues of free will and so on. I'm trying to think of movies where it does happen and there must be some, but that would be good.

There’s also something else I’d like to see. There’s a time travel science fiction story that’s a favorite of philosophers, Robert Heinlein's All You Zombies. It’s about the idea that you end up being your own mother or father, and it's like very interesting. That would be fun to watch.

What about that trope in time travel movies, that if you meet your past self, you'll create a paradox and the universe will tear apart? Is that based on anything or is that just something someone made up for convenience?  

I don't see why there would be any problem. Imagine somebody made an exact clone of you, and they walked in the room and met you. That would be just the same, really. Imagine just being in the moment and somebody exactly the same as you walking in the door, but slightly older or slightly younger. With an exact clone or a time traveler, there wouldn't be any difference to you in meeting that person.

It would just be really weird.  

It would be pretty disturbing either way, right.