4 ms·

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

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
    > A paradox is when two contradictory things are true at the same time. No. A paradox is when two contradictory things appears to be true at the same time. It simply signifies that our model is flawed or incomplete. The grandfather problem is a paradox if our model of time travel is one which is impossible. That is the point. It is simply a way of demonstrating why there needs to be constraints that makes our more naive notions of time travel impossible. As such it constrains the set of possible valid models to those in which the grandfather paradox can't be expressed within the constraints of the model. > I wasn’t merely making up impossible scenarios; I was demonstrating how their theory gives rise to paradoxical scenarios. You've done no such thing. The paradoxical scenario you imagine can't be expressed in the model I proposed, and so it solves the paradox.
vidarh 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. It is entirely irrelevant what it is. The point is that if the system is immutable it is impossible to represent a combination of state transitions that alters an existing state, as such the set of possible space-time combinations would in that case only include those where the time travel does not introduce a paradox that depends on change. The same way the timeline does not include any states where I fold an elephant, because it's not possible to do so. You have not presented any paradoxes that can work with an immutable space-time other than perhaps if said space-time introduces divergent timelines at any point of mutation, in which case the paradox can also easily be resolved. > 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! You can experience it that way, but your "do something" step 2 would be deterministic and could not possibly include steps that introduced a paradox. > There’s absolutely nothing hard about the concept of time being immutable; You're still thinking in terms of a mutable space-time. I did not talk about time being immutable, but the entirety of space-time. Your "do something" step does nothing that changes anything in an immutable space-time, because everything is fixed from the start. Nothing moves. No action is taken. Everything is unalterable. Time, and cause and effect, in that scenario is simply an illusion of consciousness at every point of a fixed 4d (or more) canvas that never changes in any way. > The true puzzle is time travel which introduce paradoxes, which your original comment says absolutely nothing about. My original comment gave immutability as an example of a possible solution. Time travel with paradoxes is not possible. That is the entire point of a paradox: The problem as stated reveals a problem with the presumed model. The solution is to identify and remove flaws in the model. Removing mutability is one such solution.
- yrimaxi 6y ago
  > It is entirely irrelevant what it is. The point is that if the system is immutable it is impossible to represent a combination of state transitions that alters an existing state, Alters? Aha! But you cannot alter that which is immutable! Seems that you still don’t get the concept. See how silly it is to language police people on such subjets? > would in that case [only include those] where the time travel does not introduce a paradox that depends on change. Highlighted the problematic part with brackets. This is just hand-waving. “Only those”? Your theory would have to be able to explain concrete examples like the grandfather problem, or else it doesn’t rise to the level of being a theory that can explain the paradox. > The same way the timeline does not include any states where I fold an elephant, because it's not possible to do so. Irrelevant unless there is an actual elephant folding paradox that I’m missing. Impossible things can be explained; paradoxes cannot since they reveal a contradiction in the model. > You have not presented any paradoxes that can work with an immutable space-time other than perhaps if said space-time introduces divergent timelines at any point of mutation, in which case the paradox can also easily be resolved. This is the first time (?) you’ve mentioned divergent timelines or hinted at non-just-straight-line-time. And yes, that would probably be perfectly adequate, and is the best answer you’ve given thus far. > You can experience it that way, but your "do something" step 2 would be deterministic and could not possibly include steps that introduced a paradox. “Determinism” is either irrelevant or non-sufficient. “Could not possibly” is pure hand-waving as there is nothing which makes sure that you are able to do something benign (like greet your former self) but not do something like kill yourself. > You're still thinking in terms of a mutable space-time. I did not talk about time being immutable, Wow, I have to hand it to you. I did mention “space-time” once (although only once) and I utterly failed to be rigorous and spell out the whole package deal, namely space-time. What an utter embarrassment. Not that it changes my point in any way. > My original comment gave immutability as an example of a possible solution. Time travel with paradoxes is not possible. You can’t resolve the Barber Paradox by simply saying that the Universe wouldn’t allow the barber to shave himself. That’s effectively what you’re doing here, only using vaguely hard science terms with a seasoning of “you still don’t get it”.
EliRivers 6y ago
You've made a hell of a mess of all this. The premise presented is simple. The past is fixed, the universe is consistent, if you travel back in time that always happened. You're saying there's a puzzle about something that the premise at hand simply says is impossible. You might as well imagine being able to create energy out of nothing and then say that's a puzzle in a universe in which we have conservation of energy. Just because you can imagine something impossible doesn't make it a paradox. And I’ll reiterate: I accept all of these premises No you don't. You keep saying "but what if you go back and change the past?"

Dylan16807 6y ago

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
  > A paradox is when two contradictory things are true at the same time. No. A paradox is when two contradictory things appears to be true at the same time. It simply signifies that our model is flawed or incomplete. The grandfather problem is a paradox if our model of time travel is one which is impossible. That is the point. It is simply a way of demonstrating why there needs to be constraints that makes our more naive notions of time travel impossible. As such it constrains the set of possible valid models to those in which the grandfather paradox can't be expressed within the constraints of the model. > I wasn’t merely making up impossible scenarios; I was demonstrating how their theory gives rise to paradoxical scenarios. You've done no such thing. The paradoxical scenario you imagine can't be expressed in the model I proposed, and so it solves the paradox.

vidarh 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. It is entirely irrelevant what it is. The point is that if the system is immutable it is impossible to represent a combination of state transitions that alters an existing state, as such the set of possible space-time combinations would in that case only include those where the time travel does not introduce a paradox that depends on change. The same way the timeline does not include any states where I fold an elephant, because it's not possible to do so. You have not presented any paradoxes that can work with an immutable space-time other than perhaps if said space-time introduces divergent timelines at any point of mutation, in which case the paradox can also easily be resolved. > 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! You can experience it that way, but your "do something" step 2 would be deterministic and could not possibly include steps that introduced a paradox. > There’s absolutely nothing hard about the concept of time being immutable; You're still thinking in terms of a mutable space-time. I did not talk about time being immutable, but the entirety of space-time. Your "do something" step does nothing that changes anything in an immutable space-time, because everything is fixed from the start. Nothing moves. No action is taken. Everything is unalterable. Time, and cause and effect, in that scenario is simply an illusion of consciousness at every point of a fixed 4d (or more) canvas that never changes in any way. > The true puzzle is time travel which introduce paradoxes, which your original comment says absolutely nothing about. My original comment gave immutability as an example of a possible solution. Time travel with paradoxes is not possible. That is the entire point of a paradox: The problem as stated reveals a problem with the presumed model. The solution is to identify and remove flaws in the model. Removing mutability is one such solution.

yrimaxi 6y ago
> It is entirely irrelevant what it is. The point is that if the system is immutable it is impossible to represent a combination of state transitions that alters an existing state, Alters? Aha! But you cannot alter that which is immutable! Seems that you still don’t get the concept. See how silly it is to language police people on such subjets? > would in that case [only include those] where the time travel does not introduce a paradox that depends on change. Highlighted the problematic part with brackets. This is just hand-waving. “Only those”? Your theory would have to be able to explain concrete examples like the grandfather problem, or else it doesn’t rise to the level of being a theory that can explain the paradox. > The same way the timeline does not include any states where I fold an elephant, because it's not possible to do so. Irrelevant unless there is an actual elephant folding paradox that I’m missing. Impossible things can be explained; paradoxes cannot since they reveal a contradiction in the model. > You have not presented any paradoxes that can work with an immutable space-time other than perhaps if said space-time introduces divergent timelines at any point of mutation, in which case the paradox can also easily be resolved. This is the first time (?) you’ve mentioned divergent timelines or hinted at non-just-straight-line-time. And yes, that would probably be perfectly adequate, and is the best answer you’ve given thus far. > You can experience it that way, but your "do something" step 2 would be deterministic and could not possibly include steps that introduced a paradox. “Determinism” is either irrelevant or non-sufficient. “Could not possibly” is pure hand-waving as there is nothing which makes sure that you are able to do something benign (like greet your former self) but not do something like kill yourself. > You're still thinking in terms of a mutable space-time. I did not talk about time being immutable, Wow, I have to hand it to you. I did mention “space-time” once (although only once) and I utterly failed to be rigorous and spell out the whole package deal, namely space-time. What an utter embarrassment. Not that it changes my point in any way. > My original comment gave immutability as an example of a possible solution. Time travel with paradoxes is not possible. You can’t resolve the Barber Paradox by simply saying that the Universe wouldn’t allow the barber to shave himself. That’s effectively what you’re doing here, only using vaguely hard science terms with a seasoning of “you still don’t get it”.

EliRivers 6y ago

You've made a hell of a mess of all this. The premise presented is simple. The past is fixed, the universe is consistent, if you travel back in time that always happened. You're saying there's a puzzle about something that the premise at hand simply says is impossible. You might as well imagine being able to create energy out of nothing and then say that's a puzzle in a universe in which we have conservation of energy. Just because you can imagine something impossible doesn't make it a paradox. And I’ll reiterate: I accept all of these premises No you don't. You keep saying "but what if you go back and change the past?"