7.5 KiB
[D] Modelling time travel in fiction
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Author: u/None *
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Score: 11
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Created: 2014-02-03T15:40:01
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u/alexanderwales [+3] Time flies like an arrow (an hour later)
I love time travel with a burning passion, and this is one of my favorite bits of summation.
The biggest thing that I can add here is that the "Single Sensitive History" and "Multiple Sensitive History" have one big distinction between them - if you're in the Single Sensitive History universe, you can never see the time machine work unless you're inside it. Single Sensitive History also seems like it can get trapped in a loop pretty easily - if the universe gets stuck in a self-consistent loop, it just keeps rewriting itself.
I also think that short-shrift is given to the BTTF model, which you can make much more consistent than it is in the movie. When someone goes backwards in time, the changes propagate forward at n seconds per second. If the rate is two seconds per second, after I go backwards in time two minutes, you would have one minute to do whatever you wanted before you were overwritten. This is the form used in the RTS game Achron. Of course, you'd have to change a lot of BTTF if you wanted to make this work - the fading pictures thing wouldn't really work, you'd have to do a dramatic countdown instead.
Also, one of my favorite time travel possibilities is having the universe look like one model of time travel while being a different model of time travel. Terminator uses Fixed History, while Terminator 2 uses Sensitive History (or multiple timelines if you don't trust what the characters say), and I've always thought that was more of a feature than a bug.
u/AmeteurOpinions [+3] Finally, everyone was working together. (2 hours later)
His article on using the English language to describe time travel is also worth reading.
I once outlined a story about a student who through absurd chance accidentally invents a time-travel device that fits in a backpack. It takes an eight foot sphere backwards or forwards in time (but not space, relative to the earth) according to the commands issued via smartphone. However, it cannot go back before it was invented and going forwards is ludicrously dangerous because you don't know what's going on at your destination.
However, this story was a Single Loop (sort of) which leads to dozens upon dozens of instances of the protagonist, antagonist, and various other characters all running around and trying to solve the chaos over the course of a single weekend. It was the sort of story where the protagonist forms a squad of himself to carry out tasks. From the outside it looks lik the task happened only once, while to him he experienced it X times, as a different instance each time.
u/RMcD94 [+1] (16 hours later)
I really don't like fixed time travel. It might make sense on the face of it, but it quickly becomes the case that any time travel in the universe would have to be iniated/designed by the universe.
And it almost completely breaks as soon as you remember the universe is made of atoms not even getting to the quantum. To even concieve that all the atoms would somehow perfectly return to the exact poisition and speed so they can complete a stable loop is just so absurd. Also it requires the universe has no random elements or free will.
u/alexanderwales [+3] Time flies like an arrow (a day later)
Funny enough, this is the widely accepted solution to the problem of the closed timelike curves predicted by certain solutions of general relativity - the Novikov self-consistency principle.
u/autowikibot [+2] (a day later)
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#### Novikov self-consistency principle:
The Novikov self-consistency principle, also known as the Novikov self-consistency conjecture, is a principle developed by Russian physicist Igor Dmitriyevich Novikov in the mid-1980s to solve the problem of paradoxes in time travel, which is theoretically permitted in certain solutions of general relativity (solutions containing what are known as closed timelike curves). Stated simply, the Novikov consistency principle asserts that if an event exists that would give rise to a paradox, or to any "change" to the past whatsoever, then the probability of that event is zero. In short, it says that it is impossible to create time paradoxes.
^Interesting: ^Closed ^timelike ^curve ^| ^Time ^travel ^| ^Many-worlds ^interpretation ^| ^Novikov ^conjecture
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u/p_prometheus [+1] These are not sins of omission but signs of preoccupation. (3 days later)
Also it requires the universe has no random elements or free will.
Of course. It's generally thought to be deterministic.
u/None [+1] (6 days later)
Nah. We know the universe has some randomness built in at the quantum level. We just also know that our cognitive processes are largely built out of much higher-level interactions where true quantum-level randomness almost definitely plays no part.
Which means that our descendents could possibly make fun of us for not having had as much free will as them, because they've got real randomness built into the part of their minds that's supposed to be random.
u/FeepingCreature [+1] GCV Literally The Entire Culture (27 days later)
Nah. We know the universe has some randomness built in at the quantum level.
Actually, no. And even if it was so, free will has nothing to do with randomness. Do see.
It can be argued whether broad readership of LessWrong would make the world a better place. It can hardly be doubted, however, that it'd greatly improve the field of philosophy.
u/Suitov [+1] The Culture (14 days later)
Neal Asher's Cowl has an interesting model of time travel. I couldn't even begin to summarise it, but it was fun.