Comments on: Time Travel Movies

By: Chad Brooks

Chad Brooks — Tue, 02 Sep 2003 21:19:44 +0000

If the course is hot limited to movies check out Poul Anderson’s time travel stories. Jack Finney’s first time travel book Time and Again is also a must (but not the sequel).

By: Tom T.

Tom T. — Mon, 01 Sep 2003 18:45:02 +0000

There have also been time travel stories that posited that the amount of energy required to travel backward through time rises asymptotically toward infinity the farther back one tries to go, so that a time traveler could never go back farther than, say eighty years from the invention of her machine. In this scenario, we are just too far in the past for any time traveler to have gotten here. Yes, there are obvious problems with this explanation; I’m just alerting you that it’s been raised.

By: Brian Weatherson

Brian Weatherson — Mon, 01 Sep 2003 03:05:55 +0000

I was going to spend some time on that argument, but I realised I didn’t have a whole lot to say about it. Here’s two things one might say: (1) We have met time travellers, they’ve just been very well disguised. There are some books that take that line, but it’s obviously not the most plausible thing in the world. (2) It turns out the only kind of time machine that is feasible requires you to put some part of the machine at either end of the travel. It’s like a telephone – you can talk across long distances but only if there’s a machine of the right kind at the other end. When the first of these machines is built it will be possible to travel back to it, but since there is no such machine in 2003, no time travellers in 2003. Option (2) looks suspiciously ad hoc as a solution to the ‘no time travellers’ argument, but I’ve met a few people who take it seriously. As for what it reveals about the students who bring it up – perhaps just that they read the textbook because it has a moderately long discussion of this puzzle, including stories that follow option (1).

By: Sean O'Callaghan

Sean O'Callaghan — Mon, 01 Sep 2003 02:36:35 +0000

I would be interested to know if anyone in the class points out that the fact that no-one has ever met someone from the future and for that reason it’s probably impossible to travel back in time.

By: Brian Weatherson

Brian Weatherson — Sun, 31 Aug 2003 23:56:15 +0000

This bit gets awkward, but it is consistent with 1D time that a time traveller could go back and cause or prevent an historical event. It’s just that it must be the case that the even they cause (prevent) was (not) part of the history they were already in. If there was an oddly knowledgeable kinda nerdy red-haired Australian who played a crucial role in stopping the Cuban missile crisis turning into WWIII, then I could go back in time and be that very Australian. And since he prevented WWIII, that means I could go back in time and prevent WWIII. Indeed I better, because if I hadn’t there would have been a nuclear war in the 1960s, and we wouldn’t be here. (If you prefer you could go back and lobby for all the treaties that led to WWI. I might try and kill you though if you’re going to, just on general anti-WWI principle. Whether I succeed will depend, inter alia, on whether it really was you who did that 1910s lobbying.) It’s really hard to think about these cases, because all of our normal ways of thinking about causation involve it propagating forward through time, and the idea of time travel is that there can be backwards causation. Some people think this means time travel in 1D time is incoherent. (See, for example, the site gc mentions, which has some rather weak arguments to that conclusion.) I’m much more inclined to think that, as David Lewis said, the correct conclusion is that a world with 1D time travel would be radically different to the kind of world we normally think we inhabit. Since QM already tells us that the world we do inhabit is radically different from the one we think we do, it’s hard to know just how big a strike against time travel that is.

By: adamsj

adamsj — Sun, 31 Aug 2003 23:39:39 +0000

A minor nit to pick: While the events of “All You Zombies—” are one-dimensional, the backstory is not. The organization for which the narrator works has as its purpose going back in time and preventing or causing historical events.

By: Tom T.

Tom T. — Sun, 31 Aug 2003 16:17:02 +0000

Connie Willis has written a couple of time-travel novels using the notion that time travel is achievable, but a physical property of the universe prevents actions that would foul the timeline. Thus, a traveler by definition cannot get close enough to major events to affect them (in one book, researchers trying to visit the bombing of Coventry keep winding up in turnip fields outside the city at several days' remove). History, in her conception, is robust, with small perturbations collapsing back into a timeline that is unchanged overall. Also, another consequence of her theory of time travel is that time travelers cannot bring objects forward from the past. Because of this, after an initial flurry of interest in the technology, the corporate world gave up on time travel as a money-making proposition, so that it is now wholly the province of underfunded university researchers. The crowd on this weblog might particularly enjoy that aspect. Her first such book is Doomsday Book, about a creepy and tragic visit to England at the outset of the Black Death. Her second is To Say Nothing Of The Dog, an immensely funny Victorian-era comedy of manners, which actually hinges on the fate of a cat. The restraints built into her theory of time travel make for intricate (and generally coherent, I think) philosophical and practical puzzles, especially in the second book.

By: G C

G C — Sat, 30 Aug 2003 16:32:23 +0000

Best time travel webpage on the net, hands down: http://www.mjyoung.net/time/timeprim.html Paradox discussion and exploration.

By: G C

G C — Sat, 30 Aug 2003 16:31:30 +0000

I’d definitely like to second the recommendation of “Slaughterhouse Five.” I’m actually teaching it this semester in a course that has nothing to do with time travel, but for a time travel course, it’s spot on. 12 Monkeys is also a necessity. In terms of consistency alone, the best time travel movie ever made. I’d like to comment briefly on the Missing Marty problem. You might not remember, but the “missing Marty” is seen going back in time to 1955 at the very end of Back to the Future Part I. So there should be only one Marty at the end of the movie, because the one who grew up in that timeline is gone. But there’s still a problem. If the Second Marty can’t possibly do everything that the first Marty did because he starts with different information. He doesn’t know that Biff is a bully who runs/ruins his dad’s life, and he doesn’t know the original story of how his parents yet. (He doesn’t know the birdwatching story, for instance.) Because of this it may not even occur to him to intervene until it is too late. BTTF therefore gives us a sort of endless loop where a Marty goes back and time and mucks around in 1955, only to return to the future moments before the New Marty heads back in time to change everything around again. Marties would spring up into existence and then replace themselves forever until finally the universe hit upon a successful, self-causing, self-consistent pattern.

By: spacetoast

spacetoast — Sat, 30 Aug 2003 15:58:47 +0000

“whether the past and future are real, what (if anything) is wrong with the argument for fatalism, whether free will and determinism are compatible, how many concepts of possibility we have in our folk conceptual scheme and whether we can say something substantive about personal identity across time.” It made an awful movie, but Slaughterhouse Five seems like it would be an almost ideal springboard to this bunch you mention. That fairly recent thing with Tom Cruise deals with time by way of causality issues. Err…Peggy Sue Got Married? (shut up)

By: Bruce Baugh

Bruce Baugh — Sat, 30 Aug 2003 10:46:02 +0000

I have a theory, based in part on a general sense of Terry Gilliam’s approach to these things, that 12 Monkeys does not present a one-dimensional timeline. It’s at least possible that the man we see in the yellow coat in memories early on is not the man we see in the yellow coat in present time at the end – that the time traveler succeeded in changing the past in ways that neither he nor anyone else ever recognizes. The anime series X, now up to six discs out of, um, thirteen or so, has some very nice stuff with prophecy and destiny, and the limits on each. It’s supernatural, of course, rather than strictly scientific. (Yes, I do realize this is far too long for a class.) For the thorough-going mindfuck, there’s always David Lynch’s film Lost Highway. Now of course it’s got a literally incomprehensible moment smack in the middle, but it seems to play out quite smoothly all around that if it’s taken as a given. Minority Report is worth mentioning if you bring up the possibility that, just as we were told the prisoners all do, the protagonist is dreaming in his confinement of the perfect or at least an acceptable outcome. Donnie Darko’s a delight, and one of the most thoroughly Phildickian movies I’ve seen.

By: Matt McIrvin

Matt McIrvin — Sat, 30 Aug 2003 06:38:51 +0000

Geoff: Mathematicians like to accuse physicists of lack of rigor in their theoretical derivations, and they’re right. The reason physicists can usually get away with this is that they’ve got to make contact with real data eventually; the world has the final say. I think the reason physicists haven’t come up with a fully-fleshed-out theory of time travel is that there’s no evidence of time travel to describe with the theory, except for one-way travel into the future that isn’t particularly paradoxical. Most physicists aren’t going to spend much time on a theory of stuff that only happens in science-fiction stories. Though some have anyway, because of the odd corners of theory that impinge on this. As for Brian’s musings on the relevance of many-worlds to time travel: David Deutsch has long claimed that you can make sense of branching histories in a general-relativistic spacetime with closed timelike lines, like Gödel’s, by applying many-worlds QM to it. I’ve never been quite sure whether I believe him. Others have been trying for some time to come up with a theoretical basis for a “chronology protection conjecture” under which closed timelike lines wouldn’t ever occur in realistic situations. I remember hearing an interesting talk by Roman Jackiw years ago about a spacetime with closed timelike lines as a result of a pair of cosmic strings: he’d shown that setting this up would take infinite energy, and wondered whether this might be generalizable.

By: WillieStyle

WillieStyle — Sat, 30 Aug 2003 05:11:01 +0000

Sounds like a cool class. When I have room in my schedule next year, I’ll travel back in time to audit it. Why would you need room in your schedule?

By: Brian Weatherson

Brian Weatherson — Sat, 30 Aug 2003 04:35:44 +0000

There’s lots of good suggestions here. Thanks to everyone, and keep ‘em coming! I probably should try and defend the honour of my university/summer camp, but instead I want to expand upon my throwaway comment about T2 because it relates to some puzzles about the nature of fictional representation that I’ve been intrigued by. I agree that the most obvious reaction to T2 is that it’s incoherent, and that it probably should have been read as a warning about James Cameron’s career arc, but it has a really simple coherent interpretation. (Warning: the following will make it painfully obvious that I’m not a literature expert. C’est la blog.) What seems to make it incoherent is that we’re told that Miles Dyson invents SkyNet, and then we see him die well before SkyNet could be invented. But we never see him invent SkyNet, the main evidence for that is that Arnie says he does. So there’s an easy way to make the story consistent – Arnie simply has very mistaken beliefs about how SkyNet was invented, since obviously it was invented without Dr Dyson around. This ‘interpretation’ raises a few questions. Why does Arnie have these crazy false beliefs? Does the T-1000 have the same beliefs? If so, why is he so mistaken as well? If not, why does he follow them to Dyson’s workplace? These are all hard questions, but they have answers that are at least coherent. This is the kind of issue about time travel stories that I find most fascinating. You’d think (or at least a philosopher would think) that when we’re given really good evidence that what a character says is false, we’ll infer that the character either has false beliefs or was lying. But in T2 we don’t do either of those things – instead we infer the world is somehow incoherent. Why isn’t the simple explanation, Arnie’s history circuits are all screwed up, the preferred one? Two reasons spring out. First, in interpreting stories there’s an important phenomena (that I assume has a proper name) that sometimes characters can be framed so that they are taken to be speaking canonically. The character speaks with the voice of the author, either temporarily or permanently. It’s hard to say how or why this happens, but we usually recognise it when we see it. (Having a long monologue is a movie with relatively little talking is one way to do the framing I guess.) And when Arnie is explaining how SkyNet was built, he’s framed in just this way. So saying Arnie got it wrong implies that the author got it wrong. But authors don’t (usually) get it wrong about their own story, because it’s their story, so they get to say what happens. Still, when an author verges into incoherence we normally pull back this licence. If I start a story with, “Osama, the caretaker’s son, had his character quirks. For example he wanted to murder everyone who wasn’t a Muslim. But all things considered he was basically a decent chap.” I imagine you’ll (quite rightly) object. If Osama wants to murder 5 billion people, he’s not a decent chap, even in a fiction. And you might think that when the author says Miles Dyson invents SkyNet two years after he is blown up in a factory explosion, similarly we would say the author has gone beyond the boundaries of poetic licence. But in time travel stories we don’t say anything of the sort, and this seems to matter to how we react to T2. I guess that the reason for that is related to the reason we don’t object to the questionable coherence of Back to the Future, but that’s not really explaining what’s going on. (Disclaimer: I haven’t seen T3, so I don’t know whether this undermines the interpretation of T2 I’ve provided here.)

By: Shai

Shai — Sat, 30 Aug 2003 04:04:31 +0000

I’ve never been to Brown but i’d like to play devil’s advocate in response to tim’s anecdotal report on his experience there. Brown is a respectable 17 on the annual US News report, and according to Brian Leiter’s Philosophical Gourmet it’s tied with Yale, Cornell, and The University of Chicago for 16, at 3.4 in its overall ranking of American philosophy departments. To give an idea of what that means, I am a student of the University of Toronto which has an overall rank of 3.5 (pretty much the same as Brown, but for reasons peculiar to the method of the report probably worse) and next semester I’m taking classes with both Ian Hacking and Thomas Hurka, two very good philosophers. I expect the case for students is the same or better at Brown. And if the US News Ranking is indicative of anything, Brown in general is certainly not in the same league as Timbuktu college; not that anyone was implying that, but you get the point.