Are these predictions about the Pacific coastline true or just a coincidence?

[moving finger]

I think I am more interested in this type of "spontaneous generation of information" paradox...
I begin to like this idea: A crazy scientist who clone himself bring his clone to a time machine and send him back 50 years, and when the clone grow up, he become the scientist who clone himself...

Anyone know anything about this type of paradox? thanks.

One of the strange aspects of this type of causal loop is that it is in fact NOT a paradox! There is nothing inconsistent or self-contradictory about it, although it DOES fly in the face of our naive concepts of causality (ie that everything must have a cause).

The causal loop is entirely self-consistent and is ALLOWED by general relativity (as GR presently stands).

The causal loop implies there is something wrong either with our intuitive view of causation, or with GR...

MF

 

[moving finger]

In the case of going back in time to change the past to be inconsistent with the present, the self-consistency hypothesis says that somehow your actions will result in a consistent world. You are looking at the idea of an oracle which can tell the future infallibly. Such oracles have appeared in fiction, and the moral is invariably that although what they say is true, it is also highly misleading.

This is what I am trying to get at.
I suspect there is something wrong with the idea that my mother can know infallibly that she will give birth to me at some future date, (similarly there is something wrong with the idea that anyone, including myself, can ever know infallibly at some time in the past that she will give birth to me at some future date), ie there is something wrong with the idea of infallible foreknowledge.

Why? Because the mere fact of possessing such infallible foreknowledge gives one powers which seem to be unrealistic (for example being "unkillable").

MF

 

[moving finger]

Hi Jesse

Actually, I wasn't imagining that you had the ability to interact with the universe--the computer will just split out complete histories, all you can do is view them.

Actually, sorry to correct you, but you asked :

What would be your response to a being in such a simulated universe who made the same arguments?

I'm not sure how I can respond to such beings (as you suggest) without interacting with them?

But in these histories, there may be simulated intelligent beings who learn to time travel, and a time traveler may meet another being and tell him in advance what he was going to do. So if this being asks the time traveler, "but what will prevent me from doing something different?", I'm asking you what you think the best answer to him would be if you were to imagine responding to him in your head, you can't actually tell him the answer since you are not part of the simulation.

Agreed, we may not interact with the simulation because to do that would require modifying the simulation.

I believe the answer to your question is that, whilst I as an external observer can have infallible foreknowledge of the simulation, no being within the simulation can have infallible foreknowledge.

Let me put a question of my own.

Suppose we grant the power of infallible foreknowledge to being (A) within the simulation (A does not have to be a time-traveller, but to keep it within the context of this thread we should make A a time-traveller), and suppose (A) then tells another being (B) that the statement (C) "B will have two eggs for breakfast tomorrow" is true.

Are you seriously suggesting that (B) is then constrained to ensuring that (C) is true, ie that he/she must have 2 eggs for breakfast tomorrow, and he/she can do nothing to avoid that coming to pass?

Either there is something wrong with the idea of infallible foreknowledge (within the simulation), or you have to posit some very strange constraints on B's ability to choose what he/she will have for breakfast.

I think the assumption of infallible foreknowledge is the culprit.

Therefore, to my mind the correct answer to your question "but what will prevent me from doing something different?" is simply : "ummmm, well nothing actually, because (since I am part of this simulation and I am interacting with you) I don't really have infallible foreknowledge of your actions, therefore I do not actually know what you are going to do..."

MF

 

[moving finger]

Don't you see the problem with your logic?

1: Yes, universes where you can travel back in time would be permitted
2: Universes where you stuck a gun to your mother's head would be permitted, but ONLY THOSE IN WHICH YOU DIDN'T SHOOT.

For example, you go up to your mother, put the gun to her head, and a police officer shoots you. Or she starts to cry and you decide you can't do it. Or you just decide you don't want to do it. ETC

No, I do not see the problem with my logic.

In fact, the logic suggests that such a scenario is not realistic.

Imagine instead that I go back in time and I tell my brother what he will have for breakfast tomorrow (let's say two eggs). Are you seriously suggesting to me (once I tell him this) that my brother is constrained to having two eggs for breakfast tomorrow, and there is absolutely nothing he can do to prevent it (regardless of whether one believes in free will or not, whatever that might be!)?

I suppose your "logic" conclusion would lead you to say "yes, even though he is told in advance that he will eat two eggs for breakfast tomorrow, there is in fact absolutely nothing he can do to avoid eating two eggs for breakfast tomorrow, it is written in stone"?

Whereas my logic conclusion would be : "There must be something wrong with at least one of the assumptions!"

And the shakey assumption I would suspect is the assumption that anyone can have infallible foreknowledge of a future in which he/she participates.

MF

 

[JesseM]

Actually, I wasn't imagining that you had the ability to interact with the universe--the computer will just split out complete histories, all you can do is view them.

Actually, sorry to correct you, but you asked :

What would be your response to a being in such a simulated universe who made the same arguments?

I'm not sure how I can respond to such beings (as you suggest) without interacting with them?

Like I said, what I was imagining was that you were formulating a mental response in your head, but yes, the question was ambiguous. Also, I was just repeating the same question I had asked in post #12 on this thread, and in that one I did spell out what I meant:

If this computer program generated a particular history for you to examine, then just by knowing the rules the computer used to do so, you could know with 100% certainty that any time travel would be perfectly self-consistent, right? So suppose you examine it, and see that somewhere in spacetime intelligent life evolved, and one of the simulated beings was asking the same questions you're asking. Since the history is already complete you can't actually interact with this simulated being, but if you wanted to think up an appropriate response in your mind, what would it be?

I believe the answer to your question is that, whilst I as an external observer can have infallible foreknowledge of the simulation, no being within the simulation can have infallible foreknowledge.

Why not? Suppose you are looking at such a simulation spit out by the computer, and in it you see that a simulated being travels back in time and tells a second simulated being about some of his future actions. Do you agree that this second simulated being now knows what he's going to do in the future, and he does not have the power to avoid it? If so, why can't you imagine the same would be true for you if a time traveler came back and told you what you were going to do in the future?

Suppose we grant the power of infallible foreknowledge to being (A) within the simulation (A does not have to be a time-traveller, but to keep it within the context of this thread we should make A a time-traveller), and suppose (A) then tells another being (B) that the statement (C) "B will have two eggs for breakfast tomorrow" is true.

Are you seriously suggesting that (B) is then constrained to ensuring that (C) is true, ie that he/she must have 2 eggs for breakfast tomorrow, and he/she can do nothing to avoid that coming to pass?

Of course. Remember, this simulation was selected by the computer because it is self-consistent, so if A sees B having eggs for breakfast one day, then goes back in time and tells him about it, how could the history possibly be self-consistent if B didn't do so?

Either there is something wrong with the idea of infallible foreknowledge (within the simulation), or you have to posit some very strange constraints on B's ability to choose what he/she will have for breakfast.

Are you suggesting that the thought-experiment involving the computer that generates a near-infinite number of possible histories, and then throws out all the ones that don't obey the laws of physics at every point in spacetime, is somehow logically impossible? If not, then it seems you must agree that the output of this computer program would be only self-consistent histories, and that if the laws of physics allow backwards time travel, then some of these histories must feature time travelers telling other simulated beings what they are going to do in the future. And you can also see that the computer does not need any specialized rules to constrain the behavior of such beings, the fact that they must take the action they were told they would is just a consequence of the fact that the computer will only output histories that obey the laws of physics at every point in spacetime (and are thus completely self-consistent).

If you disagree with any of this, which part are you disagreeing with?

 

[moving finger]

Why not? Suppose you are looking at such a simulation spit out by the computer, and in it you see that a simulated being travels back in time and tells a second simulated being about some of his future actions. Do you agree that this second simulated being now knows what he's going to do in the future, and he does not have the power to avoid it?

From whose perspective are we looking now?
I agree that from my perspective outside the simulation, as long as I do not interact with the simulation, then I can have "infallible foreknowledge" of what the beings will do, and they do just that.
However, from the perspective of someone inside the simulation, I do not believe that infallible foreknowledge necessarily works, ie it can fail, because we now have the possibility of infinite self-referential loops. If the second simulated being is told what he is going to do, you are suggesting that, armed with this knowledge, he is then necessarily constrained to do it? I don't think so.

Remember, this simulation was selected by the computer because it is self-consistent, so if A sees B having eggs for breakfast one day, then goes back in time and tells him about it, how could the history possibly be self-consistent if B didn't do so?

It couldn't be self-consistent in this case, we agree on that point - hence there must be something wrong with the assumptions. Where we differ is that you conclude from this that infallible foreknowledge is possible and it is the SCH hypothesis which ensures consistency; whereas I conclude from this that the assumption of infallible foreknowledge is at fault, and incorrect foreknowledge then ensures consistency.

Are you suggesting that the thought-experiment involving the computer that generates a near-infinite number of possible histories, and then throws out all the ones that don't obey the laws of physics at every point in spacetime, is somehow logically impossible?

No, I'm suggesting the assumption of infallible foreknowledge is at fault.

If not, then it seems you must agree that the output of this computer program would be only self-consistent histories, and that if the laws of physics allow backwards time travel, then some of these histories must feature time travelers telling other simulated beings what they are going to do in the future. And you can also see that the computer does not need any specialized rules to constrain the behavior of such beings, the fact that they must take the action they were told they would is just a consequence of the fact that the computer will only output histories that obey the laws of physics at every point in spacetime (and are thus completely self-consistent).

If you disagree with any of this, which part are you disagreeing with?

I disagree with the idea that someone can (come from the future and) tell me exactly what I will have for breakfast tomorrow, and (no matter what I do) I simply cannot prove him/her wrong. This seems absurd to me, but obviously not to you (you would presumably be happy with this notion since it is compatible with the SCH hypothesis).

One way to escape this absurdity is to suggest that the notion of infallible foreknowledge is faulty.

Let me provide a very simple model that shows the flaw in the assumption of infallible foreknowledge. It does not involve free will (whatever that is) and it does not even involve human choices; it is a purely mechanistic, deterministic algorithm.

Suppose we have a simple machine within our "life" simulation with one input and one output.

Let us also suppose that the input must be a single binary digit, either 0 or 1. Similarly the output must also be a single binary digit, either 0 or 1.
Let us suppose that the machine is hardwired such that when the input is 0 then the output is always 1, and when the input is 1 then the output is always 0, and the conversion from input to output happens instantaneously.
We also suppose that the machine is precise and infallible, and that it cannot "dither" or select an indeterminate output.
The final rule is : If someone tells the machine what it's output will be at a particular time, then it uses this supposed "prediction" as its input for that particular time.

We now have a (possibly infinite) self-referential loop.

However, the machine is perfectly deterministic. From outside the simulation, if I know the input then I also know the output. Hence I can predict what the machine will do as long as I do not interact with it.

But can anyone inside the simulation predict to the machine what the machine's output will be at a particular time? No, this is not possible, because no matter what we predict, the machine will use this as input and will output the opposite.

The SCH hypothesis would presumably say that the machine will break down, or will continuously switch infinitely fast between 0 and 1, or will produce an indeterminate output?

Whereas my hypothesis would simply say : The machines' output is just not predictable from within the simulation, time travel or no time travel.

MF

 

[JesseM]

From whose perspective are we looking now?
I agree that from my perspective outside the simulation, as long as I do not interact with the simulation, then I can have "infallible foreknowledge" of what the beings will do, and they do just that.
However, from the perspective of someone inside the simulation, I do not believe that infallible foreknowledge necessarily works, ie it can fail, because we now have the possibility of infinite self-referential loops. If the second simulated being is told what he is going to do, you are suggesting that, armed with this knowledge, he is then necessarily constrained to do it? I don't think so.

Well, do you agree that from your perspective outside the simulation, if you see that a particular history contains a time traveler, and that time traveler observes what another simulated being does on thursday and then travels back in time to wednesday and tells him about it, that the non-time-traveler now knows what he is going to do on thursday and cannot do anything different? Of course from his perspective, he couldn't be sure that the time traveler wasn't lying, so I guess it's not "infallible" foreknowledge in that sense. But it is infallible in the sense that if the time traveler isn't lying, then this being is absolutely guaranteed to do what the time traveler told him he'd do.

It couldn't be self-consistent in this case, we agree on that point - hence there must be something wrong with the assumptions. Where we differ is that you conclude from this that infallible foreknowledge is possible and it is the SCH hypothesis which ensures consistency; whereas I conclude from this that the assumption of infallible foreknowledge is at fault, and incorrect foreknowledge then ensures consistency.

Are we still just talking about the computer simulation thought-experiment, rather than the real world? I'd like to stick to this thought-experiment, because in this case we know that the "SCH hypothesis" is true. So when you talk about "incorrect foreknowledge", are you just talking about the time traveler lying, or mistaking someone's twin brother for that person, or something of that nature?

I disagree with the idea that someone can (come from the future and) tell me exactly what I will have for breakfast tomorrow, and (no matter what I do) I simply cannot prove him/her wrong.

But do you disagree that this can happen to a simulated being in the thought-experiment, where time travel is possible and where the SCH hypothesis is guaranteed to be correct in any history the computer spits out?

Let me provide a very simple model that shows the flaw in the assumption of infallible foreknowledge. It does not involve free will (whatever that is) and it does not even involve human choices; it is a purely mechanistic, deterministic algorithm.

Suppose we have a simple machine within our "life" simulation with one input and one output.

Let us also suppose that the input must be a single binary digit, either 0 or 1. Similarly the output must also be a single binary digit, either 0 or 1.
Let us suppose that the machine is hardwired such that when the input is 0 then the output is always 1, and when the input is 1 then the output is always 0, and the conversion from input to output happens instantaneously.
We also suppose that the machine is precise and infallible, and that it cannot "dither" or select an indeterminate output.
The final rule is : If someone tells the machine what it's output will be at a particular time, then it uses this supposed "prediction" as its input for that particular time.

We now have a (possibly infinite) self-referential loop.

However, the machine is perfectly deterministic. From outside the simulation, if I know the input then I also know the output. Hence I can predict what the machine will do as long as I do not interact with it.

But can anyone inside the simulation predict to the machine what the machine's output will be at a particular time? No, this is not possible, because no matter what we predict, the machine will use this as input and will output the opposite.

Well, since we're guaranteed to get only self-consistent histories, then assuming this machine was 100% accurate, then in any history containing such a machine, no time traveler would end up feeding the machine's output back to itself as input (just like no time traveler would end up murdering their own mother before they were conceived). However real people aren't like that machine, even if they intend to avoid doing something tomorrow I assume there'll always be some small chance they'll do it anyway, so unlike with the case of the machine there could be self-consistent histories in which a person is told what they are going to do tomorrow and ends up doing exactly that.

The SCH hypothesis would presumably say that the machine will break down, or will continuously switch infinitely fast between 0 and 1, or will produce an indeterminate output?

No, none of those would be self-consistent, because the time traveler apparently remembers it having given a definite output in the future. And switching "infinitely fast" doesn't sound like something that would be allowed by the laws of physics.

 

[TheUnknown]

Hi all, i just signed up today! i think this is the best site i have ever been to. Time Travel cannot be used to go back in time and change OUR future outcomes. These "future outcomes" would be future outcomes in OUR world, how do we know they would occur in another time? And if we did go back and try to protect a future outcome, we might totally mess up someone else world. On another note, if there are multiple worldlines, then how can you assume that all the same people will even be born? on a serious note, this is totally serious.. say somehow.. my dad was born in another timeline, and the day i was supposed to be born, he decided to pleasure himself, and my sperm was lost?! I believe, If you can imagine time travel, then you have to be open to multiple world lines, which in turn means that none of these would be the same, and going back in time to a "perfect" worldline that fits ours, and interacting with ANYONE's life, would totally mess everything up. I believe distorting time is very possible... but i am not sure how we'd be able to harness this, and domesticate it to go back in time... and then for what? if it is ever created it should be kept top secret and left alone. Why do we need to go back in time if everything i just stated is correct. Thanks :) i'd love a reply, i have a lot of unanswered questions, I've been reading and studying this stuff for about 6 months now, and i have never once expressed my opinion, so i am itching! :P

 

[moving finger]

Well, do you agree that from your perspective outside the simulation, if you see that a particular history contains a time traveler, and that time traveler observes what another simulated being does on thursday and then travels back in time to wednesday and tells him about it, that the non-time-traveler now knows what he is going to do on thursday and cannot do anything different? Of course from his perspective, he couldn't be sure that the time traveler wasn't lying, so I guess it's not "infallible" foreknowledge in that sense. But it is infallible in the sense that if the time traveler isn't lying, then this being is absolutely guaranteed to do what the time traveler told him he'd do.

I disagree. Later in your post you agree the binary machine I suggested is not "absolutely guaranteed" to do what it is told it will do - and the self-consistent "escape" from this scenario is that the only self-consistent history is one in which nobody ever predicts to the machine what it will do (thereby saving consistency). If this solution can be suggested for a simple machine then I see no reason why the same solution cannot be suggested for a complex human, or a simulated agent.

The solution to ensuring consistency is therefore NOT that someone can predict what I will have for breakfast and I am then constrained to have that, but instead that nobody ever successfully and infallibly predicts what I will have for breakfast!

Are we still just talking about the computer simulation thought-experiment, rather than the real world? I'd like to stick to this thought-experiment, because in this case we know that the "SCH hypothesis" is true. So when you talk about "incorrect foreknowledge", are you just talking about the time traveler lying, or mistaking someone's twin brother for that person, or something of that nature?.

It could be any of these, the important thing is that the time-traveller simply cannot have infallible foreknowledge.

But do you disagree that this can happen to a simulated being in the thought-experiment, where time travel is possible and where the SCH hypothesis is guaranteed to be correct in any history the computer spits out? .

If the simulated being (agent) is sufficiently complex then I think it is possible for any such being to then "behave" like the binary machine I have outlined, whereby it takes a prediction and deliberately tries to falsify that prediction. I cannot see why any sufficiently complex agent could not behave in this fashion, in which case your suggested solution (I believe) is either that the agent is constrained to do as predicted, or that it will never happen within the simulation that another agent makes an infallible prediction about the first agent's behaviour.

Well, since we're guaranteed to get only self-consistent histories, then assuming this machine was 100% accurate, then in any history containing such a machine, no time traveler would end up feeding the machine's output back to itself as input (just like no time traveler would end up murdering their own mother before they were conceived).

OK, I think you have agreed that what happens in this case is that there is no infallible foreknowledge possible, therefore no infallible predictions are made. I do not see why this solution cannot also be applied in the cases with simulated agents or in the case of real human beings - ie not that we are constrained to do exactly as a time-traveller predicts we must do, but that it is simply not possible for a time traveller to make infallible predictions (in most cases) in the first place.

However real people aren't like that machine, even if they intend to avoid doing something tomorrow I assume there'll always be some small chance they'll do it anyway, so unlike with the case of the machine there could be self-consistent histories in which a person is told what they are going to do tomorrow and ends up doing exactly that.

Yes, I agree this could happen, but is highly unlikely, and the overwhelmingly most likely scenario is in fact that no infallible predictions will be made in the first place.

MF

 

[moving finger]

Hi all, i just signed up today! i think this is the best site i have ever been to.

Welcome, and I hope you enjoy!

Time Travel cannot be used to go back in time and change OUR future outcomes.

By definition, if they ARE our future outcomes then they cannot be changed (otherwise they wouldn't BE our future outcomes, would they?).

These "future outcomes" would be future outcomes in OUR world, how do we know they would occur in another time?

Not sure I understand the question here?

And if we did go back and try to protect a future outcome, we might totally mess up someone else world.

Are you assuming multiple worlds/universes?

On another note, if there are multiple worldlines, then how can you assume that all the same people will even be born?

One possible solution to some of the paradoxes of time-travel is to posit multiple universes (in fact there would have to be an infinite number of parallel universes, one corresponding for each "decision" at a quantum level)

on a serious note, this is totally serious.. say somehow.. my dad was born in another timeline, and the day i was supposed to be born, he decided to pleasure himself, and my sperm was lost?!

Yes, but fortunately for you he was with your mother instead

I believe, If you can imagine time travel, then you have to be open to multiple world lines, which in turn means that none of these would be the same, and going back in time to a "perfect" worldline that fits ours, and interacting with ANYONE's life, would totally mess everything up.

There are those in this thread who believe in something we are calling the Self Consistent Histories (SCH) hypothesis, which basically means that nothing get's messed up

I believe distorting time is very possible... but i am not sure how we'd be able to harness this, and domesticate it to go back in time... and then for what? if it is ever created it should be kept top secret and left alone.

Why?

Why do we need to go back in time if everything i just stated is correct.

Because we are curious animals?

MF

 

[JesseM]

I disagree. Later in your post you agree the binary machine I suggested is not "absolutely guaranteed" to do what it is told it will do - and the self-consistent "escape" from this scenario is that the only self-consistent history is one in which nobody ever predicts to the machine what it will do (thereby saving consistency).

No, I agreed that if the machine is 100% guaranteed to work properly (to give the opposite output as its input), then the only self-consistent escape would be for no time travelers to feed its ouput back as input. However, if the machine has even a small chance of malfunctioning and returning the same ouput as its input--say, an 0.000000000001% chance--then there will be at least some self-consistent histories in which a time traveler does feed its output back to it as input, and it malfunctions and returns an output identical to its input. Such histories may be much less likely than histories where a time traveler doesn't mess with it at all, but they are not nonexistent.

And human behavior is so complex that I doubt there is any situation in which you could say, without knowing the details of what was going on in a person's brain (and without having traveled in time), that they were 100% guaranteed to do anything. Imagine humans have spread throughout the galaxy, and there are 500 quadrillion humans alive on different planets. If I go to each one pretending to be a time traveler and say "I know you will have eggs tomorrow for breakfast", then each one is filmed having breakfast tomorrow and all the films showing people having something other than eggs are thrown out, are you suggesting we could be confident there wouldn't be a single film in which someone did decide to have eggs the next day?

The solution to ensuring consistency is therefore NOT that someone can predict what I will have for breakfast and I am then constrained to have that, but instead that nobody ever successfully and infallibly predicts what I will have for breakfast!

Yes, that is one solution, and it may be that it's by far the most likely one, but there would be at least some self-consistent histories where a person was told what they were going to do by a time traveler, even if they were extremely rare.

It could be any of these, the important thing is that the time-traveller simply cannot have infallible foreknowledge.

I don't agree there is any reason they "simply cannot" have such knowledge, and you have given no real arguments for why they can't besides a vague feeling of free will (even though you know this doesn't apply to the computer simulation thought-experiment).

If the simulated being (agent) is sufficiently complex then I think it is possible for any such being to then "behave" like the binary machine I have outlined, whereby it takes a prediction and deliberately tries to falsify that prediction.

If it's complex, then even if it decides to try to act like that binary machine, it may get distracted, or change its mind, etc. My calculator will always give the right answer for a complicated multiplication problem; a human, with its complex brain, will sometimes get it wrong.

I cannot see why any sufficiently complex agent could not behave in this fashion

Well, surely you agree it is also possible for any sufficiently complex agent to decide to see what his friend eats on thursday and then go back in time and tell him on wednesday--yet your solution to the self-consistency problem was that no agent would ever choose to do so. So why doesn't your argument "I cannot see why any sufficiently complex agent could not behave in this fashion" also apply here? And if you can see that self-consistency might imply that no agent would choose to give a friend foreknowledge in this way, why can't you also see that it might imply that no agent would ever choose to behave like your binary machine, or why no agent would ever choose to kill his mother before he's conceived?

in which case your suggested solution (I believe) is either that the agent is constrained to do as predicted, or that it will never happen within the simulation that another agent makes an infallible prediction about the first agent's behaviour.

The second one is just another way of saying that any time-traveling agent is "constrained" not to choose to tell his friend what he'll eat the next day, so I don't see why you'd prefer the second to the first. Anyway, like I said, as long as it is possible for an agent to occasionally do exactly what he is predicted to do, then there should be at least some self-consistent histories in which he does receive such an infallible prediction.

Yes, I agree this could happen, but is highly unlikely, and the overwhelmingly most likely scenario is in fact that no infallible predictions will be made in the first place.

If we're getting into the domain of likelihood, it also seems unlikely that time travel would be widely available yet no time traveler would ever decide to make an infallible prediction, so perhaps the most likely type of self-consistent history would simply be one where sentient beings simply never invent time travel, even if it is permitted by the laws of physics.

 

[TheUnknown]

haha indeed... we are just very sophisticated curious animals. ok, ok, i meant... what if i went back in time, supposing that i could warn someone of some catostrophic event that is going to happen(not in nature... assuming the Earth ages the same and almost all the same geological catastrophes happen in synch with normalcy to our Known universe/world)... how do i know this will happen in their world? how do i know if that person(s)even exist in where i am going? on a differnt subject. if we do have parallel universes in the world.. as far as living things go? and we all just happen to be born in these parellel universes because of some unknown mystery yet to be figured out. Then why go back? to save yourself in another universe which is you... but won't actually effect "YOU"... i think there is a huge information gap involved with the discussion of time travel, and there always will be until we can figure it out (which i do believe is not to far off), Also about the Dad thing, i meant if my dad has lost that sperm when i went back in time.. acknowledging the fact that we have free will in all of these parallel universes. Then where i went to find myself, i would not find... but i would still find my Dad... and possibly a child that took my place :)(being that he still marries my Mom) very interesting... love the feed back, i think this is brain food, not tuna. ha. Maybe I'm missing something here? but i don't see how even in parallel universes... (whatever that means in full.. i'd love a total explanation...) how are we denied the right to free will? this theory does not mix well with my logic. :)

 

[Alkatran]

You can tell your brother that he will eat two eggs only if this won't cause him to not eat two eggs according to the 'select valid spacetimes' theory.

It's not that, given the assumption that your brother has free will, he literally CAN'T deviate from this page, it's that he WON'T. All the timelines where he decides not to are destroyed, therefore he must.

Your problem is that you're mixing science with free will.

 

[TheUnknown]

without free will we don't have science... it's not a problem.. or maybe it is? maybe this means time travel can never exist. If there is someone living that is me right now in a parallel universe... why are you so certain he will not get in a car crash and die tomorrow whereas here, i keep on living? Please tell me where science explains that. So you're image of parallel universes is a bunch of robots programmed running around doing the EXACT same things with no free will? that is not Science...

 

[TheUnknown]

also so all of his timelines are "destroyed" where he decided not to? so this is just a figment of imagination then? how can they be destroyed? what causes this destruction? so the universes aren'yt really real? they can be destroyed and created according to actions made by the free will of time travelers? so say two time travelers that live in the same wordline will meet each other in their own timeline in the year 2040. so if time traveler A lives in the year 2036, and then he travels to 2040, finds out some things about time traveler B, they meet (and become friends from then 'till 2060+), then travels to the year 2061 and time traveler B tells A something that will happen while he's in 2061 (Example eggs... so all other universes where he does/doesn't are destroyed), and then travels to the year 2000... time traveler B lives in the year 2060... he travels to the year 2000 also... by some anomalis accurance they both meet up, they both tell each other what they are and aren't going to do... so the whole universe is theoretically "destroyed" because of two time travelers? or could this is theory never happen because the year 2061 would not exist for time traveler A to meet time traveler B? So i think we do have parallel universes... but only we can access our OWN parallel universes... we could never time travel into a world where we weren't born? so there are infinite worldlines, with infinite outcomes, and infinite different human beings in each one. And also if you continuously jumped back and fourth between universes telling people what would happen you would be destroying the universe? i don't understand this theory... it makes no sense to me and is utterly and completely wrong. But then again if religios nuts are right and we shouldn't be messing with this stuff... maybe we will destroy our universe by time travel according to that theory. Basically what that theory there is projecting is that time travel destroys the universe. Here's another one, say time traveler A and time traveler B are brothers... A travels to the previous morning and tells his brother he will eat two eggs.. his brother doesn't, so all the ones where he did are destroyed... he then travels back to the next day again where he left from... he then travels back to the previous day again... tells his brother he will eat 2 eggs... his brother does... so the others are destroyed... again their whole known universe is destroyed by time travel? and if it's not destroyed yet... then what if brther B does the exact same thing to brother A... would that finish off the universe? that theory is eeeeextremeeely faulty! it's saying that you can destroy the whole universe by traveling in time and telling someone something haha.. it really sounds like something the government would say to keep people away from time travel. Really though.. is that a real theory that is trusted by scientists and astrologist? i hope not... so any day now a time traveler could come and we could all vanish because our timeline would be "destroyed" if he told someomne how many eggs they were going to eat... wow.. lol, sounds more like wishful thinking than scientific analysis and hypothesis by trial and error.

 

[TheUnknown]

if you put a man in a room, and set the clock to 12:30 and have him wake up from a banging noise (so he can wake up at 12:30)... and set the day to Monday April 4th on his calender... record him and watch what he does... take that man, brain wash him... leave his calendar alone, set his clock to 12:30 again, and do it all over, are you certain he will make the exact same choices? is this in any way different from parallel universes? and if so, how? are we predetermined to make decisions? and if so, why do you think this? If we commit the same actions in every single universe, then sending a time traveler back to ONE of them, would totally mess it up... then what happens? just that one universe is messed up, and the rest of us go on unparallel to it? or is it instantly and mysteriously "destroyed" ...? nice convo btw :)

 

[Ich]

Those multiple universes are not a theory, they are rather an interpretation of quantum mechanics which happen to solve some paradoxes of time travel.
Besides that, nobody knows if time travel really exists and so all this thread is speculation, more or less a "what if" scenario. It´s just fun talking about and letting your thoughts flow. Hope you don´t have a problem with that.
p.s. multiple universes are thought by some people to be a rather straightforward interpretation of QM; the only real alternative today is the "copenhagen interpretation" - I´d like to see your reaction to IT.

 

[moving finger]

No, I agreed that if the machine is 100% guaranteed to work properly (to give the opposite output as its input), then the only self-consistent escape would be for no time travelers to feed its ouput back as input. However, if the machine has even a small chance of malfunctioning and returning the same ouput as its input--say, an 0.000000000001% chance--then there will be at least some self-consistent histories in which a time traveler does feed its output back to it as input, and it malfunctions and returns an output identical to its input. Such histories may be much less likely than histories where a time traveler doesn't mess with it at all, but they are not nonexistent.

Agreed. I did make the initial assumption that the machine would not malfunction, but I agree with you that if there is a non-zero chance of malfunctioning then there would be at least some self-consistent histories within GR which involve a time-traveller predicting the machine's output. However I believe the overwhelming odds would be that such a prediction would not be possible (because the probability of the machine malfunctioning is so small), hence for each possible universe where such a prediction is made, there would be an overwhelming number of possible universes where such a prediction cannot be made. And I believe similar statistics would be true of the prediction of human actions.

And human behavior is so complex that I doubt there is any situation in which you could say, without knowing the details of what was going on in a person's brain (and without having traveled in time), that they were 100% guaranteed to do anything. Imagine humans have spread throughout the galaxy, and there are 500 quadrillion humans alive on different planets. If I go to each one pretending to be a time traveler and say "I know you will have eggs tomorrow for breakfast", then each one is filmed having breakfast tomorrow and all the films showing people having something other than eggs are thrown out, are you suggesting we could be confident there wouldn't be a single film in which someone did decide to have eggs the next day?

Well firstly if you do go to each one and merely pretend to be a time traveller then you do not have infallible foreknowledge and it makes no difference whether they have eggs or not does it?
But even if you were a real time traveller, I am not saying this. What I am saying is that I believe there would be an overwhelming number of instances where people "could" manage to falsify your so-called infallible prediction, and hence by your own account the prediction is simply not possible and therefore cannot be made in the first place.

Yes, that is one solution, and it may be that it's by far the most likely one, but there would be at least some self-consistent histories where a person was told what they were going to do by a time traveler, even if they were extremely rare.

I think we agree.

I don't agree there is any reason they "simply cannot" have such knowledge, and you have given no real arguments for why they can't besides a vague feeling of free will (even though you know this doesn't apply to the computer simulation thought-experiment).

No, it's nothing to do with free will, and yes I have in fact given a very real argument supporting the idea that agents cannot exercise infallible foreknowledge. It’s to do with self-referential loops. We have seen that even a simple machine can negate the possibility of usefully using apparently infallible foreknowledge through the use of a very simple self-referential loop, and the same idea can be extended to humans and other agents.

If it's complex, then even if it decides to try to act like that binary machine, it may get distracted, or change its mind, etc.

It "may" fail, but I believe in the overwhelmingly likely number of cases it will succeed.

Well, surely you agree it is also possible for any sufficiently complex agent to decide to see what his friend eats on thursday and then go back in time and tell him on wednesday--yet your solution to the self-consistency problem was that no agent would ever choose to do so.

By your own argument - there must be instances where the agent CANNOT do as you suggest if we are to maintain self-consistency. All I am arguing is that these cases will be the overwhelmingly most likely cases. However cases where agents DO travel back in time and DO successfully predict another agent's future, whilst theoretically possible in principle (at least according to GR as it stands today), will necessarily be extremely rare.

So why doesn't your argument "I cannot see why any sufficiently complex agent could not behave in this fashion" also apply here? And if you can see that self-consistency might imply that no agent would choose to give a friend foreknowledge in this way, why can't you also see that it might imply that no agent would ever choose to behave like your binary machine, or why no agent would ever choose to kill his mother before he's conceived?

I never said that it was not possible for an agent to choose not to kill his mother. Of course an agent can choose not to kill his mother, that is not the issue here. What I objected to was the implication that no agent could ever kill his mother, even if he so chose.

The second one is just another way of saying that any time-traveling agent is "constrained" not to choose to tell his friend what he'll eat the next day, so I don't see why you'd prefer the second to the first.

There is a big difference.
One solution (the self-consistent histories solution) implicitly assumes that both time-travel and infallible foreknowledge are possible, and that somehow additional “constraints” are placed on agents’ abilities in the present time to ensure consistency with both.
The other solution (the impossibility of infallible foreknowledge) does not assume time-travel, and does not place any additional constraints on agents’ abilities in the present time. In addition, it might turn out in the end that we find there is something wrong with GR as it stands, and time-travel is simply not possible (which would be consistent with the “impossibility of infallible foreknowledge” solution).

Anyway, like I said, as long as it is possible for an agent to occasionally do exactly what he is predicted to do, then there should be at least some self-consistent histories in which he does receive such an infallible prediction.

Agreed, but this neither proves that time travel is possible, nor does it prove that such histories actually exist (only that they are possible in principle assuming GR as it stands).

If we're getting into the domain of likelihood, it also seems unlikely that time travel would be widely available yet no time traveler would ever decide to make an infallible prediction, so perhaps the most likely type of self-consistent history would simply be one where sentient beings simply never invent time travel, even if it is permitted by the laws of physics.

This is closer to what I believe is the truth – but I would go even further and suggest the simplest solution of all is that in fact time travel is not permitted by the laws of physics, we just haven’t realized it yet.

MF

 

[TheUnknown]

Those multiple universes are not a theory, they are rather an interpretation of quantum mechanics which happen to solve some paradoxes of time travel.
Besides that, nobody knows if time travel really exists and so all this thread is speculation, more or less a "what if" scenario. It´s just fun talking about and letting your thoughts flow. Hope you don´t have a problem with that.
p.s. multiple universes are thought by some people to be a rather straightforward interpretation of QM; the only real alternative today is the "copenhagen interpretation" - I´d like to see your reaction to IT.

It's not my opinion though, I'm pretty sure i just proved it to be factually flawed?

 

[TheUnknown]

or if i didn't prove it wrong, i proved if time travel is possible we can destroy the universe accoring to this theory.. i'll go check out that other stuff btw thanks for the link :)

 

[moving finger]

haha indeed... we are just very sophisticated curious animals. ok, ok, i meant... what if i went back in time, supposing that i could warn someone of some catostrophic event that is going to happen(not in nature... assuming the Earth ages the same and almost all the same geological catastrophes happen in synch with normalcy to our Known universe/world)... how do i know this will happen in their world?

How do you know there is more than one world?

how do i know if that person(s)even exist in where i am going?

You cannot warn soemone who does not exist.

on a differnt subject. if we do have parallel universes in the world

That's a very big IF

.. as far as living things go? and we all just happen to be born in these parellel universes because of some unknown mystery yet to be figured out. Then why go back? to save yourself in another universe which is you... but won't actually effect "YOU"

One wouldn't necessarily want to go back to save oneself. As I said, humans are curious animals, or maybe we just want to escape from our existing future and find another future?

... i think there is a huge information gap involved with the discussion of time travel, and there always will be until we can figure it out (which i do believe is not to far off), Also about the Dad thing, i meant if my dad has lost that sperm when i went back in time.. acknowledging the fact that we have free will in all of these parallel universes.

lol - what is "free will"?

Then where i went to find myself, i would not find... but i would still find my Dad... and possibly a child that took my place :)(being that he still marries my Mom) very interesting... love the feed back, i think this is brain food, not tuna. ha. Maybe I'm missing something here? but i don't see how even in parallel universes... (whatever that means in full.. i'd love a total explanation...) how are we denied the right to free will?

Define free will first, then we can debate whether it exists...

MF

 

[moving finger]

You can tell your brother that he will eat two eggs only if this won't cause him to not eat two eggs according to the 'select valid spacetimes' theory.

It's not that, given the assumption that your brother has free will, he literally CAN'T deviate from this page, it's that he WON'T. All the timelines where he decides not to are destroyed, therefore he must.

Your problem is that you're mixing science with free will.

Your problem is that you assume I am arguing in favour of, or on the basis of, free will. Read the posts - I am not.

There will be an overwhelming number of times that you cannot infallibly tell your brother he will eat two eggs, because he can prove you wrong. Therefore the vast majority of times you simply will not be able to make the infallible prediction (you can make a prediction, yes, but most times you will be wrong). This has nothing to do with free will, but everything to do with self-referential loops.

MF

 

[moving finger]

nobody knows if time travel really exists and so all this thread is speculation, more or less a "what if" scenario. It´s just fun talking about and letting your thoughts flow. Hope you don´t have a problem with that.

I have no problem with it, Ich, but if you read the first post in the thread you will see what its all about. According to GR as it stands today, time travel is theoretically possible - ie it is not ruled out by current theories. In this thread we are simply exploring some of the implications of that.

multiple universes are thought by some people to be a rather straightforward interpretation of QM; the only real alternative today is the "copenhagen interpretation" - I´d like to see your reaction to IT.

I disagree. There are a number of interpretations of QM apart from Copenhagen and multiple universes, including the Hidden Variables interpretation. However the various interpretations of QM are off-topic for this thread.

MF

 

[Ich]

or if i didn't prove it wrong, i proved if time travel is possible we can destroy the universe accoring to this theory.. i'll go check out that other stuff btw thanks for the link :)

You just found out that time travel brings you a great deal of trouble, vanishing universes maybe the least of it. People here know that, and that´s why they´re discussing a lot.
BTW , time trave really is speculation, but i´m sure there are two or three things about the behaviour of our universe which would lead you to PROVE it wrong in less than five minutes ;)

 

[moving finger]

without free will we don't have science...

? pardon? what does science have to do with something called free will? What is this thing you call free will anyway?

it's not a problem.. or maybe it is? maybe this means time travel can never exist. If there is someone living that is me right now in a parallel universe...

How can someone else be you, unless they really are you, and you them?

why are you so certain he will not get in a car crash and die tomorrow whereas here, i keep on living?

that's the whole idea of parallel universes, that different things can happen given the same starting conditions

Please tell me where science explains that. So you're image of parallel universes is a bunch of robots programmed running around doing the EXACT same things with no free will? that is not Science...

free will, what's that again?

MF

 

[Ich]

moving finger,

admitted, GR allows for time travel under certain conditions. It also allows for wormholes and superluminal velocities, if you just can gather enough exotic matter. Don´t misunderstand me, I welcome discussion about it and enjoy it myself. Nevertheless it´s speculation, because we´re just beginning to explore the consequences of GR - already knowing that it cannot be strictly correct (TOE and so on).
To QM, i thought Bohm ran into problems with his hidden variables, and decoherence is up to date. But You´re right, that´s another forum.

 

[moving finger]

BTW , time trave really is speculation, but i´m sure there are two or three things about the behaviour of our universe which would lead you to PROVE it wrong in less than five minutes ;)

ok, Ich, and with the deepest respect, go ahead and be my guest and try to prove time travel "wrong" - I'll be generous and let you have 5 days, never mind 5 minutes

MF

 

[Ich]

ok, Ich, and with the deepest respect, go ahead and be my guest and try to prove time travel "wrong" - I'll be generous and let you have 5 days, never mind 5 minutes

MF

sorry, moving finger, this one was meant for theunknown. I didn´t want him to prove time travel wrong, but out whole universe.

 

[TheUnknown]

You just found out that time travel brings you a great deal of trouble, vanishing universes maybe the least of it. People here know that, and that´s why they´re discussing a lot.
BTW , time trave really is speculation, but i´m sure there are two or three things about the behaviour of our universe which would lead you to PROVE it wrong in less than five minutes ;)

Don't get me wrong! i am not trying to prove time travel wrong, i am trying to prove it right.. but first we need to ask questions about theories, and get rid of ones that are so absurd, if we don't.. we'll never move forward... vanishing universes? i mean c'mon.. destroying the universe because you went back in time 2 times, once told your brother he was going to eat 2 eggs... he did.. so the ones where he didn't suddenly blew up, or vanished, then go again and tell him he's gunna eat two eggs, and he does.. so they vanish too, so then what are you left with? where did that theory come from? where do the universes go if they vanish? what happens to them? it sounds... extremely wishful to me. It's not that simple... well it can't be! or we'd be destroyed already, because obviously the universe is omnipresent when it comes to thinking on a time travel level, so we could have already experienced time travelers? or is it not... do you think we are the first earth/universe to reach 2005? i believe all the questions i have posted here and in my previous posts need to be applied to all time travel theories... it can't be that universes dissapear, you could not just destroy a whole dimension of Earth just from time travel, or I'm sure we'd be destroyed by now being that the universe is omnipresent ... it's really strange isn't it? arg... maybe it's only omnipresent up to our current and previous dates.. would this explain no time traveler visits? really weird.. now I'm lost lol ah.. maybe if time travel exists, then it is not used much... don't you think? or we would have seen something by now? ( i mean does not exist... being that the universe is omnipresent... no futuristic people have visited us yet saying they are time travelers with concrete evidence)

 

[moving finger]

moving finger,

admitted, GR allows for time travel under certain conditions. It also allows for wormholes and superluminal velocities, if you just can gather enough exotic matter. Don´t misunderstand me, I welcome discussion about it and enjoy it myself. Nevertheless it´s speculation, because we´re just beginning to explore the consequences of GR - already knowing that it cannot be strictly correct (TOE and so on).
To QM, i thought Bohm ran into problems with his hidden variables, and decoherence is up to date. But You´re right, that´s another forum.

Godel found a solution to Einstein's equations which allowed time travel but did not require wormholes, exotic material or superluminal velocities. It is generally recognised that within GR as it stands, time travel is possible at least in theory. As to speculation - well even the possibility of manned flight was "speculation" until someone had the curiosity and the courage to try to make it happen for real

The only problem with QM (and it's a problem for ALL interpretations, not just Hidden Variables) is that any viable solution must be non-local. This has been (ignorantly) used as a "proof" that no hidden variables theory can work (von Neumann has a lot to be blamed for!), whereas in fact non-local hidden variables theories can work.

MF

 

[Ich]

theUnknown -
absurd things/theories happen to come along every day. I didn´t say tou should believe it. My point was that you can´t actually DISPROVE it, so join the discussion and have fun.
Moving Finger -
agreed to all. Still QM is (at least) strange, and time travel is not shown to be possible.

 

[DaveC426913]

I get it. I get it!


All the thought experiements about traveling to the past and setting up a paradox make the same assumption; they make the assumption that the past is open, i.e. that it has not happened yet, i.e. that it is still possible to shoot one's mom.

The past is not the future. It has happened. We know that you will not return to the past and shoot your mother because it did not happen. (That's the one advantage of the past, that we know what (will have) actually transpired).

This plays right into the concept that time is an illusion, that past and future are merely the myopia of living creatures. If the past present and future have already been painted on the canvas (this is the "block time" referred to), then there is, simply put, no picture of our universe that was painted where a paradox occurred.

Does this mean we do not have free will? Maybe. It doesn't require the preposterous notion that some 'thing' will prevent you from pulling the trigger, it just means that the universe you are attempting to describe wherein those events occurred, is simply not in existence. You did not shoot your mother. Period.

 

[TheUnknown]

How do you know there is more than one world?


You cannot warn soemone who does not exist.


That's a very big IF


One wouldn't necessarily want to go back to save oneself. As I said, humans are curious animals, or maybe we just want to escape from our existing future and find another future?


lol - what is "free will"?


Define free will first, then we can debate whether it exists...

MF

free will... the ability to make your own decisions? if you believe in time travel you must believe in free will... because you have the free will to go back in time and mess with someone and they have thr free will to agree with you, or not agree with you, and the list goes on... when thinking about time travel you MUST incorporate free will, or certainly the universe will end, to many contradicting factors with no free will.. so by my studies over the last 6 months I've come to the conclusion of many things, that is one of them... about warning someone if they do not exist... that was my point! :) if you decide to time travel and warn someone of something.. how do you know if their parents got together and successfuly had you, or the parents of their parents? or their parents? and all the way back to the ice ages, can you imagine the probability of that happening? it all has an effect, if anyone thing is altered the whole world changes. again it's free will at work... you may be way more special than you think, you may be the only YOU in this universe/world/etc. also how could you go back to escape your future? how do you know your future? and if you did, and we did, don't you think we'd stop our own future from happening instead of escaping? we can never know our future with 100% accuracy... or so i believe, and if we did escape to another world where there was no time travel what would we tell them? how would we have enough room to fit all of humanity into another worldline? would humans be scattered through multiple universes or many worldlines? would we then warn every worldline of the possible catastrophes that lie ahead? see what i mean? this destruction of universes thing cannot exist... i can't find any reasonable logical explanation of it that i can't contradict.

 

[TheUnknown]

theUnknown -
absurd things/theories happen to come along every day. I didn´t say tou should believe it. My point was that you can´t actually DISPROVE it, so join the discussion and have fun.
Moving Finger -
agreed to all. Still QM is (at least) strange, and time travel is not shown to be possible.

i am having fun! you don;'t like me? :(

 

[Ich]

still have ;)