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Time travel paradox resolved...I think

kourama

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May 23, 2002
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I apologize if this has come up before.

I had an insight once many years ago about time travel and forgot about it until it came up in conversation the other day.

I submit my idea for review:

The well-known time travel paradox works as follows:

An engineer (let's face it, scientists never actually BUILD anything) designs and builds a device that allows her to travel backwards into time. After completing the device she decides to save herself all the work of design and goes back in time to give herself the plans to build the device. She goes back in time and gives the plans to her former self.

If her former self has the plans given to her, then who actually designed the device?

My resolution for this problem works like this: if we look at the space-time continuum so that causality always works in a positive direction in time, then the initial event would be the engineer arriving in what is perceived to be her past. Once she is there, then her perception of a personal past is an illusion. She has a set of memories, but since what she perceives as a memory has not occurred, she is not remembering a past.

From that point forward, causality works as normal, and she operates as any entity in the universe. WHen she interacts with what she perceives to be her former self, she is, in fact, interacting with a completely seperate person, on whose future she does not depend.

So, the paradox is gone, but there is a new problem: if causality works only in a forward direction in time, then what causes the initial event, which is the arrival of the 'future' engineer in the universe?

Well, if I could answer that, I'd have made a killing in the stock market by now. ;)
 
kourama said:
Once she is there, then her perception of a personal past is an illusion. She has a set of memories, but since what she perceives as a memory has not occurred, she is not remembering a past.

From that point forward, causality works as normal, and she operates as any entity in the universe. WHen she interacts with what she perceives to be her former self, she is, in fact, interacting with a completely seperate person, on whose future she does not depend.

So, the paradox is gone, but there is a new problem: if causality works only in a forward direction in time, then what causes the initial event, which is the arrival of the 'future' engineer in the universe?

Well, if I could answer that, I'd have made a killing in the stock market by now. ;)
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This doesn't seem to me to resolve anything. The freshly-existing engineer arrives with a full set of plans in her "non-memory" and a plan to communicate it to her earlier self. This violates causality any way you look at it, especially if we view causality as always happening in the forward direction. The fact that the device doesn't yet exist is irrelevant; just the existence of a plan in the engineer's head is enough to violate causality, it seems to me.
 
Even if time travel is possible the consequences far outweigh any advantages we could receive, and the potential for total time ripping chaos is high.

Time travel is a Pandora’s box that shouldn't ever be opened.
 
Re: Re: Time travel paradox resolved...I think

sundog said:


This doesn't seem to me to resolve anything. The freshly-existing engineer arrives with a full set of plans in her "non-memory" and a plan to communicate it to her earlier self. This violates causality any way you look at it, especially if we view causality as always happening in the forward direction. The fact that the device doesn't yet exist is irrelevant; just the existence of a plan in the engineer's head is enough to violate causality, it seems to me.
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Yep, which means, as far as I can tell, that the only way to travel in time is to be lucky enough to simply appear in the universe, fully formed with all the illusion of memory in tact, a la Bertrand Russel (that was his idea, right?)
 
If time travel is possible, or will ever be possible, then it's already happening, and any consequences of such have already happened. However I'm not aware of any evidence that someone from the future is paying us visits.

Oh, of course, we're the the ones traveling on the front edge, so eventually we might be able to go into the past.

Hogwash.
 
Time travel is a normal part of the quantum world. In the quantum world, particles can travel forward or backward in time.

Accordingly, it would be difficult to categorize this as a paradox. It is real.

A more accurate question is: does the future influence the past as much as the past influences the future? As best as we can tell, there appears to be an asymmetry in time. The macroscopic result is the appearance that time moves in one direction, our past "causes" our future.

But this cannot be rigorously demonstrated at the quantum level. There is nothing about the laws of physics which says there could not be matter which is moving through space-time backwards relative to our perception of time.

Hypothetically, for example, when the big bang occurred, half the energy of the newly created universe could have been sent in the other time direction from the portion of the universe we occupy. There is nothing in our understanding of physics which prevents this from being a possibility.
 
Doesn't Quantum Theory show that if such a thing happened, at that point, a new reality would be formed based on the alternation in time? But the old reality would also continue to exist. In other words, a new universe would be formed without harming the old one. Since there are thought to be (possibly) an infinite number of universes anyway, maybe this sort of thing has already happened over and over again.
 
Re: Re: Re: Time travel paradox resolved...I think

kourama said:


Yep, which means, as far as I can tell, that the only way to travel in time is to be lucky enough to simply appear in the universe, fully formed with all the illusion of memory in tact, a la Bertrand Russel (that was his idea, right?)
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Which unfortunately violates the Second Law of Thermodynamics, it seems to me.
 
My favorite time travel paradox:

The pockets in a pool table are wormholes. The wormhole in the left corner pocket is linked to the wormhole in the right corner pocket by a two second offset. If you dunk a ball in the right corner pocket, it pops out of the left corner pocket two seconds later. If you dunk a ball in the left corner pocket, it pops out of the right corner pocket two seconds earlier.

Now, you line up your shot and hit a ball into the left corner pocket, so two seconds earlier it pops out of the right corner pocket and knocks itself out of the way, causing it to miss the pocket, and hence, it could never have come out of the right corner pocket to knock itself out of the way.
 
Now, you line up your shot and hit a ball into the left corner pocket, so two seconds earlier it pops out of the right corner pocket and knocks itself out of the way, causing it to miss the pocket, and hence, it could never have come out of the right corner pocket to knock itself out of the way.

"Metaphysics gives me a headache." ---Nick Danger to Rocky Roccoco.
 
Mark said:
Now, you line up your shot and hit a ball into the left corner pocket, so two seconds earlier it pops out of the right corner pocket and knocks itself out of the way, causing it to miss the pocket, and hence, it could never have come out of the right corner pocket to knock itself out of the way.

"Metaphysics gives me a headache." ---Nick Danger to Rocky Roccoco.
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Ooh, favorite time travel paradoxes? :D

I have two. One is an Anson MacDonald (Robert Heinlein) and I forget who wrote the other.

The Heinlein one is called "By His Bootstraps" and is a complicated maze of paradoxes. It finally turns out that most of the characters in the story are one person at different times in his life. Very entertaining, classic time-travel story.

I'm not sure of the other one's name, even. It involved an archaeologist who invented a time travel machine, went into the future and came back, dying immediately but bringing with him a mysterious knife made of an unknown metal. A museum is built in his memory and the knife placed in it. Years later his grandson tries to reproduce his trip into the future and does, following his grandfather's footsteps into a bombed-out building and ending at an empty display case with the dusty outline of the knife. The grandson looks up to discover, of course, that he's in the museum built to honor his grandfather.
 
My favorite was a short story by Robert Silverberg (possibly just edited by him; I don't remember) in which time travel is highly illegal and every time any traveler is caught, he faces a judge who always convicts them and sends them to a prison on the moon. Somehow, the judge ends up trying out a time device and ends up facing himself and is sent to prison.
 
Time travel isn’t possible because time doesn’t exist

You've obviously never had to spend time with a life insurance salesman. :D
 
Mark said:
My favorite was a short story by Robert Silverberg (possibly just edited by him; I don't remember) in which time travel is highly illegal and every time any traveler is caught, he faces a judge who always convicts them and sends them to a prison on the moon. Somehow, the judge ends up trying out a time device and ends up facing himself and is sent to prison.
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I like the penalty for misusing time machines in The Hitchhikers Guide to the Galaxy: You get left back in the stone age and are told to evolve into a more responsible life form. :D
 
There was a book I read when I was a kid called The Tale of Time City. Anyone else heard of this?

It was pretty confusing, but had a very interesting premise.
 
shanek said:


I like the penalty for misusing time machines in The Hitchhikers Guide to the Galaxy: You get left back in the stone age and are told to evolve into a more responsible life form. :D
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That was the penalty for "drunk in charge of a time ship", as I recall.

OK, close enough. :D
 
Re: Re: Re: Re: Time travel paradox resolved...I think

sundog said:


Which unfortunately violates the Second Law of Thermodynamics, it seems to me.
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Not necessarily (sp?), as long as some other part of the universe is increasing in entropy proportionately. :D

Favourite time-travel story: Bill & Ted's excellent adventure. Back to the future came out at the same time, but the logic was a bit broken. Bill & Ted's future was showing up in their past and all the pieces fit together (as far as I could tell). Also, being a HUGE Dr. Who fan, I totally dug the phone booth idea.
 
If time travel is possible, or will ever be possible, then it's already happening, and any consequences of such have already happened. However I'm not aware of any evidence that someone from the future is paying us visits.
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Not that this thread is at all serious anymore.. but you're assuming here that time travel would be along a single timeline. Ie, we go back into our own past.

There's also the multiple time-line idea of time travel, where going back and changing something creates a new branch.


A B
-----------------------------------------------------------------


A C B
------------------------,. . . . . . . . . . . . . . . . . . . . . . . . .
\
\
\ D

A: the start of the time line.
B: the point you jumped from.
C: the point you jumped to.
D: the new "present", B is longer accesible to you.

It's more a way to travel through multiple universes than strict time travel.

[edit] wow. that did not work at all.
 
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