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That option implies time travel is not possible, since your mere existence at a past moment is already mutating it. Which is the opposite of what the article cl
by ricardobeat 6y ago
That option implies time travel is not possible, since your mere existence at a past moment is already mutating it. Which is the opposite of what the article claims.
- wongarsu 6y agoWhy? If time is immutable (essentially a Block Universe where everything is predetermined) then you traveling in time doesn't mutate anything, just as you experiencing the current time isn't mutating anything. Of course it (seems to) follow that you don't have any free will. But there's nothing in science or philosophy contradicting that (if anything we seem to find more and more evidence to support that idea).
- yrimaxi 6y agoI think free will is orthogonal to mutability/immutability of time.
- alisonkisk 6y agoFree will is a nonphysical illogical concept. It's impossible to define free will inside physics in a way that feels "free".
- yrimaxi 6y agoYour comment is orthogonal to my comment.
- vidarh 6y agoExactly. E.g, a possible example immutable scenario that doesn't violate anything (with each number representing a discrete period of time) 1. An old man appears and says hi to me and disappear. 2. 20 years pass. 3. I obtain a time machine. 4. I travel back in time and return (in my absence from this time period, I'm at time step 1 saying hi to myself) The key being that we tend to see this as: 1a. Nothing happens. 1b.An old man appears and says hi to me and disappear. 2. 20 years pass. 3. I obtain a time machine. 4. I travel back in time and return (in my absence from this time period, I'm at time step 1b saying hi to myself). At which point 1b looks like a change from 1a, so we conclude there's mutability. But if the universe is immutable, then 1a never existed in the first place. I always, immutably had will have (sorry, I could not resist) travelled back in time to greet myself And that removes e.g. the grandfather paradox, because a static, immutable representation of it that is consistent with our other rules (not having people spontaneously come into existence, for example) isn't possible.
- yrimaxi 6y agoI don’t think this really gets at the paradox. What if you shot yourself?
- EliRivers 6y agoYou didn't shoot yourself. We know this to be true.
- yrimaxi 6y agoOk. I guess verb tense falls short in this case. :-)
- EliRivers 6y agoIt does, but that's also the point. The past is fixed in this model. If you go back in time, that's not new. You always did that. How the present looks now is a function of you having always done that. We know that you didn't shoot yourself, because you didn't.
- yrimaxi 6y agoYes of course, except for the last part. Their temporal experience, if they went into a time machine, is: 1. Time machine backwards 2. Shoot themselves 3. Time machine forwards And that’s how they would have experienced it. The whole premise seems to be that this is allowed: 1. Time machine backwards 2. (do something) 3. Time machine forwards Of course step 2 always happened since it’s the past. And yet they shot themselves. But they couldn’t shoot themself and exist now as well. And that’s the paradox. Two choices at this point: 1. You can’t really do anything in step 2. In which case time travel is impotent, and hence why even dignify calling it time travel at all? 2. You have some potency in step 2, but you can’t do things that lead to paradoxes. But then how would you handle those special cases? Just stating that “the past is fixed” doesn’t solve the paradox, it restates one of the premises.
- vidarh 6y agoMy description explicitly hypothesised a universe that is entirely immutable, and where the passage of time is purely "read only". Your presence at any given point in time then would never mutate anything ever, any more than watching a movie mutates the movie. EDIT: You can certainly imagine more "relaxed" models that would also work, where mutability is possible, but where constraints increasingly restrain which mutations are possible when looping back on itself, but an immutable model is the simplest to describe in order to illustrate that models that allows loops can be made self-consistent.