Paradox for time travel to the past solved?

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Hello,

I am currently reading "The first Fifteen Lifes of Harry August" from Catherine Webb and really like it so far. I did not even read the half or so but there was an interesting idea I would like to discuss about.

As far as I understand Harry August does return after dying to the same point in time and space where he was born. Now he lives his life again and remembers the things from his earlier lifes. He does change things constantly compared to earlier lifes.
The idea to circumvent the problem of contradiction is - as far as I understand - the multiverse theory.
Appeared sexy to me for a moment.

If I would travel back to a tree forking then it basically doesn't matter for me if I change things. I can't return to the past before I was born so there is no contradiction to kill your parents before you are born or so.
You may change history but who cares? It is just branches in the tree which you will walk through and then you return to start again.

There are several issues I see in this picture and to be honest, I am not a friend of a multiverse concept.

For example I don't get how suddenly branches in the multiverse which existed before are whiped out. They collapse in the moment Harry is born and from the point in the future, they are suddenly gone and have never existed.

For me the multiverse concept (whatever this exactly means) does not help to avoid a serious problem: travelling to the past.

Thoughts?
 

Answers and Replies

  • #2
phinds
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My though is that traveling to the past is pure fiction so it really doesn't matter what paradoxes appear if you assume there is some form of it. I mean, if you are writing fiction, you just need to make it minimally plausible. The story-line is far more important than the science.
 
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  • #3
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My though is that traveling to the past is pure fiction so it really doesn't matter what paradoxes appear if you assume there is some form of it.
Well, the point is there is no paradox in the situation described. If you are reborn whyever, which happens to Harry August but you can remember then it would be something like a very complex (impossible) simulation.
If the mechanism in "this" universe is to create universes constantly then it makes sense to ask what happens if I insert other information in the past. Harry can do what he wants, he will never influence things before he was born - and we shouldn't ignore that there are already unlimited Harrys in other universes as far as I understand.... he will die and return. Branches will collibe suddenly...
I like that book so far but I don't get the central point of the idea. My problem (apart from quantum mechanical issues): I am me, so how can it be that I am manifold and don't know?
 
  • #4
Well, the point is there is no paradox in the situation described. If you are reborn whyever, which happens to Harry August but you can remember then it would be something like a very complex (impossible) simulation.
If the mechanism in "this" universe is to create universes constantly then it makes sense to ask what happens if I insert other information in the past. Harry can do what he wants, he will never influence things before he was born - and we shouldn't ignore that there are already unlimited Harrys in other universes as far as I understand.... he will die and return. Branches will collibe suddenly...
I like that book so far but I don't get the central point of the idea. My problem (apart from quantum mechanical issues): I am me, so how can it be that I am manifold and don't know?
You are not a manifold, you are human. Manifolds are used in physics to help scientists generalise previous statements and describe other phenomena and properties of physical reality. The three dimensions of our experience help us. More dimensions than these help physicists generalise previous statements.
 
  • #5
256bits
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I am me, so how can it be that I am manifold and don't know?
Which one is the "real" me? and could they all accuse each other of being facsimiles.

( Seems similar to being in a house of mirrors, but not quite, since each and every mirror image all act alike, and is an observation or representation from a different perspective. )
 
  • #6
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The Garden of Forking Paths by Jorge Borges also explores many of these ideas. Highly recommended.
 
  • #7
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As far as I understand Harry August does return after dying to the same point in time and space where he was born. Now he lives his life again and remembers the things from his earlier lifes. He does change things constantly compared to earlier lifes.
There's no paradox if you look at it from a multiverse standpoint as you indicate. This seems effectively to be a Groundhog Day plot (also Edge of Tomorrow, Happy Deathday...)

The problem is in the above description. You have a baby that has not yet been born with memories only gained in the womb. One second later, that baby has full memories of one or more past lives. That's a violation of causal physics. That state change is unexplained. Call it a paradox if you like. I just call it a violation. No creature just suddenly acquires experience from nowhere when it didn't have it a moment before. It's like my car rolling out of the factory with 0.0 km on the mechanical odometer, and suddenly popping to 293,000 km just like that, despite still being a new car.
 
  • #8
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That state change is unexplained.
Science fiction and even more fantasy doesn't need to explain everything.

It's like my car rolling out of the factory with 0.0 km on the mechanical odometer, and suddenly popping to 293,000 km just like that, despite still being a new car.
Yes, that would be strange. It's usually the other way around. An old car comes to the second-hand car dealer with 293,000 km on the mechanical odometer and suddenly popping to 0.0 km to be sold as new, despite still being an old car. But that also remains unexplained.
 
  • #9
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Which one is the "real" me? and could they all accuse each other of being facsimiles.

( Seems similar to being in a house of mirrors, but not quite, since each and every mirror image all act alike, and is an observation or representation from a different perspective. )
It is different as you already have understood. I am me. Explain, who can I be me, following one path, if there are so many pathes? This makes no sense to me. I think that this is a serious philosophical problem.
 
  • #10
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The problem is in the above description. You have a baby that has not yet been born with memories only gained in the womb. One second later, that baby has full memories of one or more past lives. That's a violation of causal physics. That state change is unexplained. Call it a paradox if you like. I just call it a violation. No creature just suddenly acquires experience from nowhere when it didn't have it a moment before. It's like my car rolling out of the factory with 0.0 km on the mechanical odometer, and suddenly popping to 293,000 km just like that, despite still being a new car.
Sorry if my short description of the situation wasn't too precise. In this books world you will not return into the same life if something happened which influenced the whole situation in which you died... the idea is that the world does not change significantly if you don't try to change a lot. You are simply born in the same place, same time - if you are born and nobody makes that you aren't born (which is a central part of the book).
Your example doesn't fit: Please read the book! It has many pages and many ideas. The central idea is fascinating. About your concern: No, if you are born you have a babies mind but - however - you get more and more the feeling that all of the things happened before and you even know things about the future you can't know. This happens if you are getting older. Try to remember when you began to think somehow. In those days their brains know way more.
In the book the protagonist believes he is insane in the second life and kills himself as a child, begins to accept it in the third life but with the development of the brain there is not just new things (which are mostly old things) forming the person, no: This formation is already complete - but - the person you have been when you died. So you will remember to have been although a 7 year old depressing person who killed itself.
This means the worst which could happen to you is - without the exception to not been born - to lose your identity, your memories, before you die. In that case those persons will begin to cycle again through the time and their first life is the new life and the second will be a shock, again.
I hope this is more clear to give you a picture. The situation is very complex.
 
  • #11
phinds
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It is different as you already have understood. I am me. Explain, who can I be me, following one path, if there are so many pathes? This makes no sense to me. I think that this is a serious philosophical problem.
Why a problem? Each of the "you"s thinks "I am me" and each is right.
 
  • #12
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Why a problem? Each of the "you"s thinks "I am me" and each is right.
Nope, only me is right because only me is there to reflect about myself and
to speak about me with you. I have the identity to speak with you. I follow the
path and truly, I am me.
 
  • #13
phinds
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Nope, only me is right because only me is there to reflect about myself and
to speak about me with you. I have the identity to speak with you. I follow the
path and truly, I am me.
Not to the other me you aren't.
 
  • #14
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Science fiction and even more fantasy doesn't need to explain everything.
But the OP asked, so it is fair game to say where I see violations.
For the record, I am quite a fan of this sort of plot, and I have no problem accepting the premise. I have more of an issue with stories that claim to be real physics, and then violate it. The movie Gravity comes to mind.

Explain, who can I be me, following one path, if there are so many pathes? This makes no sense to me. I think that this is a serious philosophical problem.
Plenty of philosophical discussion has been dedicated to this subject. I have found at least one solution to my liking that doesn't violate the law of identity, but you'd probably not like it. It serves my purpose when used in QM discussions.

Look up Derek Parfit for some in-depth reading on the subject.

Sorry if my short description of the situation wasn't too precise.
...
You are simply born in the same place, same time - if you are born and nobody makes that you aren't born (which is a central part of the book).
This is exactly the part that I protested.

Please read the book!
I am basing my reply on your posted comment, which is that <something> goes back and is born again (at least 14 times). One problem is the identity thing that 256bits brings up. What exactly is it that goes back?
2nd problem is the one I brought up: How does this baby abruptly change into one with one or more lifetimes of memory? Physics doesn't allow that.

If you want to talk about the story as a work of fiction, fine, But you brought up how contradictions might arise, and you're right.

So you will remember to have been although a 7 year old depressing person who killed itself.
This is what I mean. Babies don't suddenly acquire memories they didn't have one minute prior to 'birth'.

From the OP:

For example I don't get how suddenly branches in the multiverse which existed before are whiped out. They collapse in the moment Harry is born and from the point in the future, they are suddenly gone and have never existed.
There is no collapse in MWI interpretation. All the other worlds are still there, each evolving a different way. 'You' experiencing this one does not prevent the other ones from experiencing theirs. MWI is a nice way to resolve said paradoxes of killing your parents and such, but it still suffers from the point I made which is said abrupt state change, sort of like Marty (Back to the Future) suddenly appearing out of nowhere in a farmer field. No interpretation allows that.
 
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Not to the other me you aren't.
Who doesn't exist.
 
  • #17
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But the OP asked, so it is fair game to say where I see violations.
For the record, I am quite a fan of this sort of plot, and I have no problem accepting the premise. I have more of an issue with stories that claim to be real physics, and then violate it. The movie Gravity comes to mind.
Gravity is junk. So disappointing.
Plenty of philosophical discussion has been dedicated to this subject. I have found at least one solution to my liking that doesn't violate the law of identity, but you'd probably not like it. It serves my purpose when used in QM discussions.

Look up Derek Parfit for some in-depth reading on the subject.
Thank you, I will check this for further discussions. I think this is absolutely fundamental.
One problem is the identity thing that 256bits brings up. What exactly is it that goes back?
2nd problem is the one I brought up: How does this baby abruptly change into one with one or more lifetimes of memory? Physics doesn't allow that.
If you want to talk about the story as a work of fiction, fine, But you brought up how contradictions might arise, and you're right.
This is what I mean. Babies don't suddenly acquire memories they didn't have one minute prior to 'birth'.
Absolutely, you are right. I don't want to justify this sort of physics. Sorry. It is fiction. It makes no sense.
It is just a level higher then what I read before about time travels. I am just asking because I believe that the idea of time travel backwards is only possible in a MWI where I don't believe in.
I am quite a fan of this sort of plot, and I have no problem accepting the premise. I have more of an issue with stories that claim to be real physics, and then violate it. The movie Gravity comes to mind.
Yes, I like this plot. I haven't that much experience with jumps in time backward but this one feels good. It is written very well in my eyes.

And now you:
Plenty of philosophical discussion has been dedicated to this subject. I have found at least one solution to my liking that doesn't violate the law of identity, but you'd probably not like it. It serves my purpose when used in QM discussions.
Look up Derek Parfit for some in-depth reading on the subject.
This is exactly the part that I protested.
I will check this, thanks!
 
  • #18
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I am just asking because I believe that the idea of time travel backwards is only possible in a MWI where I don't believe in.
MWI does not allow time travel any more than any other interpretation. Less so actually since it adheres to the principle of locality, which among other things always puts cause before effect.
There are delayed choice experiments that are explained with backwards time travel (in said interpretations that choose counterfactual definiteness rather than locality). Those are more likely interpretations if you're looking for one that supports 'time travel', but even those forbid information travel to the past, and the plot of your story is definitely information travel, so it is forbidden by physics period.
 
  • #19
stevendaryl
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I think that a way to have a consistent notion of time travel is if you have infinitely many copies of Earth, each evolving deterministically, but each one is offset in time from the last by, say, an hour. Then what people think of as time travel is just ordinary spatial travel to an Earth with the appropriate time offset. So there’s no problem with meeting yourself, or killing your own Grandfather, or whatever. Those are just copies of the ones you think of as real.
 
  • #20
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Regarding how a child might gain knowledge of its subsequent life (which it can then alter), you could take a non-magical route for it and have the child stumble upon a machine and simultaneously lock its living consciousness to that moment and also gain the knowledge of its life. Each time it died, it would return to that moment where it emerges from the machine into the mind of its younger self, with the knowledge of how it lived before.

The paradox created here, of course, is that the return point is always to the same point, akin to groundhog day, so would result in infinite loops unless there was a goal to achieve to break the cycle, EG recovering this lost/stolen machine and decoupling from it.
 
  • #21
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Regarding how a child might gain knowledge of its subsequent life (which it can then alter), you could take a non-magical route for it and have the child stumble upon a machine and simultaneously lock its living consciousness to that moment and also gain the knowledge of its life.
How does the machine acquire this information that it imparts to the child? It is effectively a foretelling of a future, which can be done with a book, but we make it a fancy machine that can directly transfer the information as memory. I can agree to that except for the part where the device has this information to give, which it doesn't.

Each time it died, it would return to that moment
What exactly is returning here? An old man is carried to the past? A message is sent to the machine? All that is time travel, and is magic/fiction.

It all sounds kind of like tomb raider, where Lara Croft saves the state of the universe (tomb) at certain points and can resume from that point if something goes wrong, all with memory of the prior failure. That isn't time travel, it is simply setting the state of the universe the same way it was a short time before, a mere violation of thermodynamic law, but not a violation of locality. It works because Lara doesn't carry her own memories, so the universe that is exactly as it was a minute ago doesn't reset those memories. The memories are external to the universe, and thus preserved over the reset.
 
  • #22
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I guess it would be that the machine opens some sort of link between the information stored in the persons memory and the moment it is activated, which means that the person would go on to live their life (by their point of view) and then when they died, reappear at that moment with the memories they had accumulated, which the machine just put into their mind.

Interestingly, if the machine was meant to be switched on and then switched off again (but was left on) then the individual would keep looping until they managed to turn it off (or, in the case of groundhog day, managed to get it off). However, the only evidence there would be of their other "lives" would be their own memories. So, realistically, the timeline would be that the child picked up the machine, gained memories of dozens of lives which didn't involve turning off the machine, and then turned off the machine, with no actual time-travel needed. The machine could instead have been predicting courses of action, and give the user perspective of that via a neural upload, and not really have gained information from the future at all.
 
  • #23
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The machine could instead have been predicting courses of action, and give the user perspective of that via a neural upload, and not really have gained information from the future at all.
In the story the process of gaining the information isn't defined. It is as it is. Yes, I agree, let us say that it is just an upload. If you think about a simulated universe this makes very much sense. Why not to inject a person subprocess to find out how this changes the story?
 

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