Time travel
Dec. 5th, 2006 04:38 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
jackThere are many different conceptions of time travel (including of prophecy) in fiction. Most start with someone's gut reaction of how it should work, and then someone explains laws of physics which would produce that effect.
* There is one universe of which the future is fixed and normally but not always unknowable. This covers everything descended from Greek myths like Oedipus, that assumed prophecies were fixed and likely to come about due to efforts to prevent them.
* Whenever you change the past, the future evolves naturally from there, but you continue to exist from that point onward even if there's no past to explain your existence. This covers every story where someone goes back in time and treads on a butterfly, and discovers all society is different.
* You can change the past, but cannot make a paradox.
* You can change the past, but if you make a paradox you slowly fade out of existence. As in, Back to the Future. This doesn't entirely make sense to me -- why should the change propagate at a definite rate? And if you disappear, does the change remain? But I admit it's at least self-consistent.
* Self-causing loops can't exist (in any sort of universe).
* Self-causing loops can exist (in any sort of universe). Eg. Oedipus. If the universe is changeable, you must be able to switch from one to another. (Eg. someone in the far future events time-travel, goes back in time, and helps people invent it earlier and earlier, but it's always invented. Unless someone erases the loop and it's never invented.) There may or may not be loops which could never have evolved from a linear timeline.
* The past can be changed, but some events are very likely to happen anyway.
Question 0 These last two tend to describe the Terminator films. I don't know why everyone says their time-travel is crap, as far as I can tell: they assume anything with Arnie in is wrong about physics; they object to the fact that the characters think they learn more about time-travel physics as they experience more of it, rather than being right from the start; they object to self-causality; they object to moralising.
Two more questions:
Question 1 If you have good reason to believe that your future can't be changed, and you see [relative X] die, why do you always try to prevent it by making them be elsewhere, etc? If you set out to *fake* the death you saw, then you know what you're doing is at least possible.
Question 2 In much fiction, people's intuitive idea is that if you travel back in time beyond your own lifetime it's like normal, but if you go to your own lifetime, you appear in place of your body there. It obviously makes sense on some level, but can anyone give a physics explanation which would fit it?
* There is one universe of which the future is fixed and normally but not always unknowable. This covers everything descended from Greek myths like Oedipus, that assumed prophecies were fixed and likely to come about due to efforts to prevent them.
* Whenever you change the past, the future evolves naturally from there, but you continue to exist from that point onward even if there's no past to explain your existence. This covers every story where someone goes back in time and treads on a butterfly, and discovers all society is different.
* You can change the past, but cannot make a paradox.
* You can change the past, but if you make a paradox you slowly fade out of existence. As in, Back to the Future. This doesn't entirely make sense to me -- why should the change propagate at a definite rate? And if you disappear, does the change remain? But I admit it's at least self-consistent.
* Self-causing loops can't exist (in any sort of universe).
* Self-causing loops can exist (in any sort of universe). Eg. Oedipus. If the universe is changeable, you must be able to switch from one to another. (Eg. someone in the far future events time-travel, goes back in time, and helps people invent it earlier and earlier, but it's always invented. Unless someone erases the loop and it's never invented.) There may or may not be loops which could never have evolved from a linear timeline.
* The past can be changed, but some events are very likely to happen anyway.
Question 0 These last two tend to describe the Terminator films. I don't know why everyone says their time-travel is crap, as far as I can tell: they assume anything with Arnie in is wrong about physics; they object to the fact that the characters think they learn more about time-travel physics as they experience more of it, rather than being right from the start; they object to self-causality; they object to moralising.
Two more questions:
Question 1 If you have good reason to believe that your future can't be changed, and you see [relative X] die, why do you always try to prevent it by making them be elsewhere, etc? If you set out to *fake* the death you saw, then you know what you're doing is at least possible.
Question 2 In much fiction, people's intuitive idea is that if you travel back in time beyond your own lifetime it's like normal, but if you go to your own lifetime, you appear in place of your body there. It obviously makes sense on some level, but can anyone give a physics explanation which would fit it?
no subject
Date: 2006-12-05 06:28 pm (UTC)Question 2: plot device.
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Date: 2006-12-05 06:35 pm (UTC)2. I already know it can be arbitrarily decided with a plot device because it is :) It's better than that, it makes some sense intuitively which is enough to make a good narrative. What I want to know if there could ever be a *consistent* explanation, or will it forever be "just bcause"? :)
no subject
Date: 2006-12-05 06:46 pm (UTC)2. Um, I continue to think there isn't a very good consistent explanation, therefore it's just a plot device :) Seriously though, I can only think of e.g.s where someone goes back in their own lifetime and their younger self *is* there...
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Date: 2006-12-05 06:36 pm (UTC)no subject
Date: 2006-12-06 01:40 pm (UTC)no subject
Date: 2006-12-05 09:14 pm (UTC)no subject
Date: 2006-12-06 01:38 pm (UTC)