4 ms·

Yes 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. T

Yes 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 ago
You're still thinking of this as a chain of events unfolding, rather than as a playback of a set of immutable, self-consistent events. > The whole premise seems to be that this is allowed: No. That was not the premise. The premise was an immutable representation of self-consistent state transitions, so what occurs in step 2 will always have occurred at that point in time, because otherwise the system isn't immutable. Step 1. just links step two into the causal chain of events in a way necessary to make the existence of 2. consistent. Again: Think of a graph. An immutable graph. The flow of time in this model simply follows the graph. It doesn't do anything at all, it just replays the events. The problem here is thinking about this as if there are choices being made as time passes. > Just stating that “the past is fixed” doesn’t solve the paradox, it restates one of the premises. It's not stating the past is fixed. It's stating everything is fixed.
- yrimaxi 6y ago
  And I’ll reiterate: I accept all of these premises! I’ve never denied them! All you and Eli have managed to do at this point is try to nitpick the linguistic deficiencies of my explanations, which are inevitable anyway since I’m not a physicist with a specialization in space-time theories. And whether I “get it” or not is secondary to the point of whether you have truly managed to confirm or disconfirm the time travel paradox, which I still claim you have failed to do. It is simple to wave away a time travel where you do something compeletely benign, like frickin’ wave or greet your former self. Try dealing with something of consequence, like killing your former self (as in: the person in that point of time-space which carries the mutable signifier of “yourself” which is younger than yourself) or giving yourself a kilogram of gold from the future, which I think would violate the law of preservation of energy or whatever. Is time travel backwarks possible or not? If it is, see the questions in my previous comment. > No. That was not the premise. And yet if time travel backwards is possible you simply cannot deny that one would experience (!) that time travel as steps 1–3. Temporal experience. Hah! There’s absolutely nothing hard about the concept of time being immutable; that’s how children’s cartoon handle time travel, not as two timelines where the first one gets erased right after the second one “happens”. (Okay, okay, they probably use both of these tactics.) The true puzzle is time travel which introduce paradoxes, which your original comment says absolutely nothing about. But maybe you’ve answered that in another comment (I have only kept up with this subthread). If not, you should probably try to do that instead of dewelling on this minor philosophical insight of yours.
  - Dylan16807 6y ago
    > Try dealing with something of consequence, like killing your former self (as in: the person in that point of time-space which carries the mutable signifier of “yourself” which is younger than yourself) or giving yourself a kilogram of gold from the future, which I think would violate the law of preservation of energy or whatever. You can make up impossible scenarios without time travel too. Like someone that shoots themselves (lethally, thorough and immediate) and then a month later they go out to lunch and eat a ham sandwich. The ability to write out a scenario doesn't mean the scenario is possible. The theory is that "I go back in time and kill myself" is just as impossible as "I kill myself then a month later eat a ham sandwich". And for largely the same reason: both scenarios violate causality, so the universe can't be shaped that way.
    - deleted 6y ago
      [deleted]
    - yrimaxi 6y ago
      Shooting yourself and then later going out to lunch is simply impossible; it is not a paradox. A paradox is when two contradictory things are true at the same time. The grandfather problem is a paradox if time travel is possible. If it isn’t possible then it is simply an impossibility. > And for largely the same reason: both scenarios violate causality, so the universe can't be shaped that way. So you agree that time travel is impossible. Great... we agree. However I was discussing this with someone who apparently thinks that it is concievable... I wasn’t merely making up impossible scenarios; I was demonstrating how their theory gives rise to paradoxical scenarios.
      - Dylan16807 6y ago
        > A paradox is when two contradictory things are true at the same time. > The grandfather problem is a paradox if time travel is possible. If it isn’t possible then it is simply an impossibility. It's only a paradox if you're making certain assumptions about how time travel works. You need to admit that these are assumptions. Consider the airplane on a treadmill paradox. There is a hidden assumption that it's possible to accelerate the treadmill in isolation to match the wheel speed, but the logic fails because the speed of the treadmill is entwined with the speed of the wheels on the plane. > So you agree that time travel is impossible. Great... we agree. No, that's not what I said. > I was demonstrating how their theory gives rise to paradoxical scenarios. It doesn't. You're assuming you can choose your actions independently from the time travel. The theory says that every choice is entwined with the fabric of the universe, so that by the time you see that an instance of time travel exists, the critical non-paradox-causing choices are already set in stone.

vidarh 6y ago

You're still thinking of this as a chain of events unfolding, rather than as a playback of a set of immutable, self-consistent events. > The whole premise seems to be that this is allowed: No. That was not the premise. The premise was an immutable representation of self-consistent state transitions, so what occurs in step 2 will always have occurred at that point in time, because otherwise the system isn't immutable. Step 1. just links step two into the causal chain of events in a way necessary to make the existence of 2. consistent. Again: Think of a graph. An immutable graph. The flow of time in this model simply follows the graph. It doesn't do anything at all, it just replays the events. The problem here is thinking about this as if there are choices being made as time passes. > Just stating that “the past is fixed” doesn’t solve the paradox, it restates one of the premises. It's not stating the past is fixed. It's stating everything is fixed.

yrimaxi 6y ago
And I’ll reiterate: I accept all of these premises! I’ve never denied them! All you and Eli have managed to do at this point is try to nitpick the linguistic deficiencies of my explanations, which are inevitable anyway since I’m not a physicist with a specialization in space-time theories. And whether I “get it” or not is secondary to the point of whether you have truly managed to confirm or disconfirm the time travel paradox, which I still claim you have failed to do. It is simple to wave away a time travel where you do something compeletely benign, like frickin’ wave or greet your former self. Try dealing with something of consequence, like killing your former self (as in: the person in that point of time-space which carries the mutable signifier of “yourself” which is younger than yourself) or giving yourself a kilogram of gold from the future, which I think would violate the law of preservation of energy or whatever. Is time travel backwarks possible or not? If it is, see the questions in my previous comment. > No. That was not the premise. And yet if time travel backwards is possible you simply cannot deny that one would experience (!) that time travel as steps 1–3. Temporal experience. Hah! There’s absolutely nothing hard about the concept of time being immutable; that’s how children’s cartoon handle time travel, not as two timelines where the first one gets erased right after the second one “happens”. (Okay, okay, they probably use both of these tactics.) The true puzzle is time travel which introduce paradoxes, which your original comment says absolutely nothing about. But maybe you’ve answered that in another comment (I have only kept up with this subthread). If not, you should probably try to do that instead of dewelling on this minor philosophical insight of yours.
- Dylan16807 6y ago
  > Try dealing with something of consequence, like killing your former self (as in: the person in that point of time-space which carries the mutable signifier of “yourself” which is younger than yourself) or giving yourself a kilogram of gold from the future, which I think would violate the law of preservation of energy or whatever. You can make up impossible scenarios without time travel too. Like someone that shoots themselves (lethally, thorough and immediate) and then a month later they go out to lunch and eat a ham sandwich. The ability to write out a scenario doesn't mean the scenario is possible. The theory is that "I go back in time and kill myself" is just as impossible as "I kill myself then a month later eat a ham sandwich". And for largely the same reason: both scenarios violate causality, so the universe can't be shaped that way.
  - deleted 6y ago
    [deleted]
  - yrimaxi 6y ago
    Shooting yourself and then later going out to lunch is simply impossible; it is not a paradox. A paradox is when two contradictory things are true at the same time. The grandfather problem is a paradox if time travel is possible. If it isn’t possible then it is simply an impossibility. > And for largely the same reason: both scenarios violate causality, so the universe can't be shaped that way. So you agree that time travel is impossible. Great... we agree. However I was discussing this with someone who apparently thinks that it is concievable... I wasn’t merely making up impossible scenarios; I was demonstrating how their theory gives rise to paradoxical scenarios.
    - Dylan16807 6y ago
      > A paradox is when two contradictory things are true at the same time. > The grandfather problem is a paradox if time travel is possible. If it isn’t possible then it is simply an impossibility. It's only a paradox if you're making certain assumptions about how time travel works. You need to admit that these are assumptions. Consider the airplane on a treadmill paradox. There is a hidden assumption that it's possible to accelerate the treadmill in isolation to match the wheel speed, but the logic fails because the speed of the treadmill is entwined with the speed of the wheels on the plane. > So you agree that time travel is impossible. Great... we agree. No, that's not what I said. > I was demonstrating how their theory gives rise to paradoxical scenarios. It doesn't. You're assuming you can choose your actions independently from the time travel. The theory says that every choice is entwined with the fabric of the universe, so that by the time you see that an instance of time travel exists, the critical non-paradox-causing choices are already set in stone.