How to reconcile time travel
Ian | 24 November, 2008 | 20:15My Philosophy of Space and Time class is winding down, and I have a week now to think up and write my 3000 word final essay. One of the potential topics is time travel.
Now in class we figure that any “second chance” time travel is logically impossible (assuming one timeline) because it will create logical contradictions (the grandfather paradox), and that’s just not cool.
This is disappointing though. I mean, what’s the fun of time travel if you can’t do it, or if you can that you can’t change anything?
Now, I’ve also just finished Douglas Adams’ (author of Hitchhikers Guide to the Galaxy) Dirk Gently’s Holistic Detective Agency. It starts a bit slow, but once you get past the second half stuff really picks up and ends amazingly.
Here’s a quote from near the end:
“But that can’t work, can it?” said Richard. “If we do that, then this won’t have happened. Don’t we generate all sorts of paradoxes?”
Reg stirred himself from thought. “No worse than many that exist already,” he said. “If the Universe came to an end every time there was some uncertainty about what had happened in it, it would never have got beyond the first picosecond. And many of course don’t. It’s like a human body, you see. A few cuts and bruises here and there don’t hurt it. Not even major surgery if it’s done properly. Paradoxes are just the scar tissue. Time and space heal themselves up around them and people simply remember a version of events which makes as much sense as they require it to make.
“That isn’t to say that if you get involved in a paradox a few things won’t strike you as being very odd, but if you’ve got through life without that already happening to you, then I don’t know which Universe you’ve been living in, but it isn’t this one.”
Now, Douglas Adams’ work is known for its somewhat off-kilter philosophy (i.e. the God that vanished in a puff of logic) but I like the insight in this quote.
Imagine that you did go back in time and kill your own grandfather.
By this view of time, you’d still exist, and you’d remember killing your grandfather (hell, the whole world could know), but perhaps the rest of the world would convince themselves that either your grandma got around, your parent was actually conceived before he died (slow pregnancy maybe) or one of your parents were a modern Jesus (in terms of virgin births). The opinions of the events wouldn’t have to overlap, but would all come to the conclusion that you exist and murdered your grandfather. They would also all make perfect sense to everyone who believed them.
And remember, people believe some pretty crazy things.
Now, a view that logical impossibilities are possible poses some odd realities, however, by assuming that all conscious beings automatically assume a belief that makes some sense, we’ve essentially made an untestable hypothesis and thus run counter to science. (Remember, scientists have a hard time publishing or even believing paradoxical data).
Interesting, and great for philosophy, but hardly useful for science (which relies on the fact the universe can be made sense of, which, according to its own data, generally does).
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Another possibility (which is particularly attractive if you are a determinist) is that any events that transpire when you travel back in time already form part of the causal nexus that led to you traveling back in time and doing the things that you do. On this theory, it is impossible for you to kill your biological ancestors, but that is fine because determinism precludes you from doing most of the things that you would otherwise like to do. This may or may not be integral to the plot of Twelve Monkeys.
I guess I should have preambled with the fact I was holding onto some concept of free will (which my prof argues is still possible in a deterministic world, but that’s another argument).
I think that is probably a good thing to retain in your ontology.
Well, you don’t have to be a libertarian to have some sort of free will in play… when you get a minute, take a look at Dennett’s Freedom Evolves, which made compatibilism far more plausible to me.
That said, what about the Back to the Future or Terminator idea? That is, time travel wherein the past is actually altered really creates a branched timeline. So, taking the former as an example, when Marty went back in time and accidentally broke up his parents, he didn’t vanish from existence immediately. He created a new timeline where he and his siblings were never born. He then subsequently created a third timeline where his parents got together in a far more romantic fashion and were entirely different people. This requires distinguishing between the timeline of the world and the timeline of the person, but that doesn’t seem obviously objectionable.
Another way to go is to argue, with Kant, that time is a form of presentation not an ontological feature, in which case time travel is only a discontinuity in the order of the spatiotemporal manifold of perception.
The problem with “branched timelines” is that we don’t really have a physical basis (besides many-worlds hypothesis) for such an idea. That’s not to say it’s not possible, but it doesn’t really seem testable (how do I know what timeline I’m in?)
I’m with ADHR. The only way for this to be resolved is with the many-worlds, infinite parallel time lines. This is the ultimate free will – all things are possible and the universe is altered based on your actions and choices and branches from there.
Kinda of the bastard child of Schroedinger’s Cat and Werner Heisenberg.
Kant has nothing to do with it.
Is everything that’s real testable, though? That sounds like verificationism, which (amongst other things) failed because it ran epistemology and ontology too closely together. It’s not in principle untestable, which seems to put it in the realm of the logically possible. Whether it’s physically possible depends on what physicists are saying these days, and I concede I really have no clue what they’re on about.
Oh, and, Kant is relevant to everything, Mike. Deal.
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Devin brought up Twelve Monkeys. Just a moment, brain dirty, need a bone saw.
There does appear to be one problem with the perspective you’ve addressed even operating under the assumptions you’ve mentioned (such as single timeline and free will). Namely, that reality itself is subjective, and if enough people believe a paradox didn’t happen, it didn’t. Doesn’t this put a LOT of emphasis on a person’s individual beliefs and perspectives (almost to a Copenhagen Interpretation level)? Or am I simply not following your case (i.e. it could be that the paradox did happen but our minds construct a narrative to cover our perception of what cannot be? This sounds like an odd hybrid of Terry Pratchett and H.P. Lovecraft.)
Sorry for the double post, but on a related note: If my last parenthetical is the case (i.e. that the mind covers up paradoxes that otherwise actually happened), this leads to a horrible, horrible pun worthy of this paper’s potential title: If a paradox happens in a forest, and no one’s around to see it, does the universe still end?
[...] How to reconcile time travel ’t to say that if you get involved in a paradox a few things won’t strike you as being very odd, but if you’ve got through life without that already happening to you, then I don’t know which Universe you’ve been living in, but it isn’t this one.” Now, Douglas Adams’ work is known for its somewhat … [...]