by a1s » Wed Apr 13, 2016 3:35 pm
Guest wrote:a1s wrote:
Stable time loop (a.k.a "immutable time-line"): You can travel to the past (and "affect" it) but you can't actually change it, since your present is already the result of you going back in time. This vaguely contradicts causality.
Closed timelike curves may be capable of existing in our universe, or not, but I see nothing inherently contradictory with them. The whole point is that they are stable, so they contain no possibility of a contradiction.
I didn't say they were exactly contradictory, I don't know enough about general relativity to say one or the other. That being said, from a layman's point of view going back in time (to affect it in any way. Again note how affect⊃change) seems to violate the basic rule of causality which is "stuff happens after the stuff that made it happen happened"
a1s wrote:Causality says that effect must happen after cause (and in fact at least d/c seconds after, where d is distance between where the cause and effect happen, and c is the speed of light) that means that time travel violates it, in any cases that matter.
(If finding out your grandfather was a monster in 2010, leads you to travelling from 2020 to 2000 in order to kill him, that would mean an event in 2010 caused an effect in 2000. That's a contradiction, some would say, so time travel doesn't exist, QED.)
Note that in the above example you killed your grandfather,
after he was an abusive asshole (perhaps this was a navigation mistake on your part, or perhaps this is one of those weird Novikovian effects)
Edit: Novikov claimed that time travel (in a stable timeline) would be inherently surrounded by improbability, because the things that make the most sense from a personal-narrative point of view (such as killing grandpa
before he caused harm, which was the whole point of the trip) are statistically eliminated as impossible due to "causing" a paradox)
[quote="Guest"][quote="a1s"]
Stable time loop (a.k.a "immutable time-line"): You can travel to the past (and "affect" it) but you can't actually change it, since your present is already the result of you going back in time. This vaguely contradicts causality.[/quote]
Closed timelike curves may be capable of existing in our universe, or not, but I see nothing inherently contradictory with them. The whole point is that they are stable, so they contain no possibility of a contradiction.[/quote]
I didn't say they were exactly contradictory, I don't know enough about general relativity to say one or the other. That being said, from a layman's point of view going back in time (to affect it in any way. Again note how affect⊃change) seems to violate the basic rule of causality which is "stuff happens after the stuff that made it happen happened"
[quote="a1s"]Causality says that effect must happen after cause (and in fact at least d/c seconds after, where d is distance between where the cause and effect happen, and c is the speed of light) that means that time travel violates it, in any cases that matter.
(If finding out your grandfather was a monster in 2010, leads you to travelling from 2020 to 2000 in order to kill him, that would mean an event in 2010 caused an effect in 2000. That's a contradiction, some would say, so time travel doesn't exist, QED.)[/quote]
Note that in the above example you killed your grandfather, [i]after[/i] he was an abusive asshole (perhaps this was a navigation mistake on your part, or perhaps this is one of those weird Novikovian effects)
Edit: Novikov claimed that time travel (in a stable timeline) would be inherently surrounded by improbability, because the things that make the most sense from a personal-narrative point of view (such as killing grandpa [i]before[/i] he caused harm, which was the whole point of the trip) are statistically eliminated as impossible due to "causing" a paradox)