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Possible or not?

I tend to think this: The paradoxes it would create make it impossible. For example, what would happen if you traveled back to before you were born and killed your mother? Would you immediately blink out of existance? What if you killed Hitler? Would the world's population of Jews suddenly EXPLODE?

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I've heard that, in one theory about time travel, it wouldn't be possible to go back before the time machine itself was invented.

3. Another is that you can travel back in time, but not into your past, but into a parallel one -- so there's no paradox. Kill your grandfather there, and that universe's "you" is never born. No problem.

The big problem with time travel is physics. Imagine a time traveler appears in front of you. Where did he come from? From your perspective, his mass did not exist until he showed up. Serious violation of mass-energy conservation.

One clever s/f story I've read had a time-travel scheme that avoided a lot of these problems. You could travel into the past, but not physically. Instead, you could briefly "posess" the body of a person from the time you wanted to visit. You couldn't choose the individual, so you were much more likely to be a stable boy than a duchess. And if you didn't get "recalled" in time, you'd forget who you were and revert to your host's personality. Minimal likelihood of changing history. Good concept, eh?

4. Here's an interesting thought that occurred to me a couple days ago.

We exist in a universe of ::mumble:: space and time dimensions, and each particle exists at a particular point of that spacetime. No matter what happens, each particle can only move a positive distance from that particular point.

We are used to the cartesian system of describing space in terms of plus and minus x, y, and z directions--and the concept doesn't seem to extend to the t, time, dimension. But is is true that the square root of x^2+y^2+z^2 is always positive, and that concept does extend to our perception of time.

Of course, x^2+y^2+z^2-t^2 is the invariant quantity for relativity, but who cares about that?

<font size=-1>[Fixed italics html]</font>

<font size=-1>[ This Message was edited by: GrapesOfWrath on 2001-11-15 08:23 ]</font>

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I don't know what Grapesofwrath is saying since he's mumbling things [img]/phpBB/images/smiles/icon_biggrin.gif[/img] , but talking with a friend in philosophy we used to have this idea.

There's no proof of it, just wishful thinking, because we prefered the universe not to be a fatalist one back in philosphy. Also because we were led in that direction by the teacher, maybe just a little. [img]/phpBB/images/smiles/icon_smile.gif[/img]

So we used to think that there is an infinite number of parallel universes, that every possibility, even if there is an infinity of possibilities, is mapped, an infinite number of ramifications. Meaning it just goes as deeply as to how one molecule bounces off another anywhere in the universe. Cause and effect. And I'd like to think that by going back in time even if you do absolutely nothing you create branches, an infinite number of ramifications, simply because you impact on how every little part will interact with the other by being there. So everytime there is any infinitely small event, branches are created for every eventuality.

Or I am just insane. This is the only thing everyone seems to agree on. [img]/phpBB/images/smiles/icon_smile.gif[/img]

On a more official note I read that "the experts" are at a stage too early to decide whether or not this is possible. At this point there is no way of deciding one way or another.

Enjoy it while you can, you'll think back to days like this in the future when we dreamed about it and it will be a big no-no at that point. [img]/phpBB/images/smiles/icon_smile.gif[/img]

If you want to hear more of the raving delusions of a madman, go on, ask and you'll get!

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I tend to think this: The paradoxes it would create make it impossible.
The great Larry Niven wrote on this subject, and came up with a strange sounding but simple rule; If the physics of a universe allow time travel, then time travel will not exist in that universe. In other words, the paradoxes negate the possibility.

Let me go on record as saying that I hate most time travel stories simply because of the paradox problem. I don't care how cleverly they are written, they are impossible!

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On 2001-11-15 21:44, The Rat wrote:

Let me go on record as saying that I hate most time travel stories simply because of the paradox problem. I don't care how cleverly they are written, they are impossible!
Some science fiction do a great job of handeling the paradox problem. Sphere is a good example. The paradox was avoided because all parties involved either died or forgot what happened, therefor the future was not changed. 12 Monkeys also did a good job of eliminating paradox by using false memory of the actual events.

8. Mr.X,
The very best science fiction story I have ever read concerning time travel and parallel time lines is "The Proteus Operation" by James P. Hogan. It starts in 1975 in a world where the Nazis won WWII and goes back to back to the start of the war as the characters try to change history. It is even better than "The Number of the Beast" by Robert A. Heinlein and you won't catch me ranking Heinlein second to anything very often! [img]/phpBB/images/smiles/icon_eek.gif[/img]

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Speaking of Heinlein (again [img]/phpBB/images/smiles/icon_smile.gif[/img]).

I never got a chance to read "The Number of the Beast", but he does a great job of time travel in "The Door into Summer". It avoids any paradox by making sure the characters were never able to do anything that could cause a paradox. They could walk all over and do almost anything, but whatever they did was incorporated into the normal timeline, and events would conspire to make sure nothing paradoxical happened. I especially remember that the main character kept on just missing himself everywhere he went. It was as if everything was fixed and couldn't happen any other way.

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On 2001-11-16 06:02, David Hall wrote:
Speaking of Heinlein (again [img]/phpBB/images/smiles/icon_smile.gif[/img]).

I never got a chance to read "The Number of the Beast", but he does a great job of time travel in "The Door into Summer". It avoids any paradox by making sure the characters were never able to do anything that could cause a paradox. They could walk all over and do almost anything, but whatever they did was incorporated into the normal timeline, and events would conspire to make sure nothing paradoxical happened. I especially remember that the main character kept on just missing himself everywhere he went. It was as if everything was fixed and couldn't happen any other way.
So it was as though time had already been written in stone? There's another theory, as well.

Speaking of books, I remember reading one story that took place in the future that was about this company that(illegally, of course) helped people go back in time, to see the dinosaurs, for example. What they would do is they would go back and create an area that, no matter what anyone did, the future wouldn't be affected. Anyway, a customer went on this trip and went off the path. When the customer got back to his time, things had changed dramatically. It was a very good story.

11. On 2001-11-16 06:44, James wrote:

Speaking of books, I remember reading one story that took place in the future that was about this company that(illegally, of course) helped people go back in time, to see the dinosaurs, for example. What they would do is they would go back and create an area that, no matter what anyone did, the future wouldn't be affected. Anyway, a customer went on this trip and went off the path. When the customer got back to his time, things had changed dramatically. It was a very good story.
Ray Bradbury's "A Sound of Thunder." A classic.

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"One clever s/f story I've read had a time-travel scheme that avoided a lot of these problems. You could travel into the past, but not physically. Instead, you could briefly "posess" the body of a person from the time you wanted to visit."

Sound a bit like "Quantum Leap"? Although I bet the story came first!

<font size=-1>[ This Message was edited by: NottyImp on 2001-11-16 08:44 ]</font>

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An interesting link here, if you have the time:

http://setis.library.usyd.edu.au/sta...e-travel-phys/

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And in an episode of the outer limits you could only see a short period of time in the future, about 15 minutes and move around in a "virtual reality" suit, but impossible to interact with anything, just see things. Nobody could see you either.

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But "just seeing" is interacting, as photons must travel from the future and impact on your retina. This means there has to be a physical - and hence causal - connection. OK, it's only a story...

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Up the Imps!

<font size=-1>[ This Message was edited by: NottyImp on 2001-11-16 09:16 ]</font>

16. Speaking of Heinlein (again ).
... and time travel (again [img]/phpBB/images/smiles/icon_smile.gif[/img] ), one of his weirdest stories is "All you Zombies". Closed loop time travel.

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On 2001-11-16 09:07, NottyImp wrote:
But "just seeing" is interacting, as photons must travel from the future and impact on your retina. This means there has to be a physical - and hence causal - connection. OK, it's only a story...
Okay, but what if, IF, I had some sort of retina in the future, but, it was only a "virtual" area shaped like a retina, and in some way, the photons are counted and measured, but go straight through? You could have a picture, right? And you wouldn't interact? Right?

Okay, I'm now certifiably insane, thanks to you, Nuttyimp! [img]/phpBB/images/smiles/icon_biggrin.gif[/img]

He was proposing as a part of dimensional theroy, that time was the fourth dimension.
And following the postulates of dimensional theroy, a dimension higher on the ladder can effect one below, but not vis versa.

For example he put forward, that a three dimensional object, casts a 2 dimesional shadow, that could be seen by a two dimensional creature, if such a thing existed, and if it was in the correct intersection plane.

A 3 dim. subject, if a creature, could however see the 2 dim. creature, and directly influance it, upto and including moving it to other locations on it's intersection plane, or other intersection planes.

However at best, the 2 dim. creature, could only get a vauge idea of what the 3 dim. creature was. It could measure it's shawdow, so to speak, and perhaps produce get and idea of shape, and using abstrat thinking, postulate about debth.

Appling this dimasional law to us, we can in a sense, see the effects of time, and in a way understand what time might be. But we will never be able to interact, or influance it, without the assistance of something from the dimension of time itself.

In essense, time travel will be impossible, as people can only see the effect of time, not interact directly with it. Time travel would require more understanding of the fourth dimension, (and possible even going to it), then any being from the third dimension could comprehend.

Again this was an old theroy I read once, and not sure with the advent of quantum mechanics and other sciences if it's even applicable anymore.

But i'm guessing it is applicable in one sence. -If- time is a dimension (so to speak) above our, were basically out of luck, in trying to influance it.

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Okay, but what if, IF, I had some sort of retina in the future, but, it was only a "virtual" area shaped like a retina, and in some way, the photons are counted and measured, but go straight through? You could have a picture, right? And you wouldn't interact? Right?
It's a lovely notion, and, hey, who knows? But it violates the rules of quantum uncertainty (as we know them at this time.) You can't "detect" a particle without altering its position and momentum. Doing that would interfere with history, at least at a very trivial level. Likely enough, intercepting a few photons would not create a causality paradox... But it *might*...

Okay, I'm now certifiably insane, thanks to you, Nuttyimp! [img]/phpBB/images/smiles/icon_biggrin.gif[/img]
Quantum weirdness is enough to drive anyone insane (let alone complex arithmetic... the square root of negative one? AIEEE!)

Silas

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I'm pretty sure Larry Niven wrote a short story in which time travel was impossible, and the time machines went to a fantasy world where time travel was possible-along with unicorns and other fun stuff.

21. On 2001-11-16 20:10, Ravi Pinjala wrote:
I'm pretty sure Larry Niven wrote a short story in which time travel was impossible, and the time machines went to a fantasy world where time travel was possible-along with unicorns and other fun stuff.
A whole series of stories, actually, collected in "The Flight of the Horse". Pretty good, but not my favorite Niven stuff.

22. On 2001-11-16 08:43, NottyImp wrote:
"One clever s/f story I've read had a time-travel scheme that avoided a lot of these problems. You could travel into the past, but not physically. Instead, you could briefly "posess" the body of a person from the time you wanted to visit."

Sound a bit like "Quantum Leap"? Although I bet the story came first!

<font size=-1>[ This Message was edited by: NottyImp on 2001-11-16 08:44 ]</font>
Now that you mention it, Quantum Leap did use that idea. The story did indeed come first. Wish I could remember the name...

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Time Travel - Y'gotta'luv'it.

Here's a interesting idea I came up with Time Travel. What if Time wasn't linear per se but rather a series of points. (I know that a series of points can be a line but stay with me here) Like a 'choose-your-own' adventure novel only certian points are available to be "jumped" to from specific points. The kicker is ALL possiblities exist but you may not be able to reach them from you present position.

One rule is that you can only go from one specific point to another specific point once or to any other point in the chain. For example, Given points A,B,C,D,E & F if you follow this series of points A-> B-> C-> A-> X-> X the next point could not be B or C or even A. Which means you would need to head to D,E,or F following one of those you could then head to any point but you could not continue up the "chain" that may have already been established.

Now it must be understood that there is and infinite number of points accounting for every conceivable situation including paradoxes. (But some of those may never be attainable.) Since all points exist with their respective matter and energy you couldn't add or subtract matter or energy from a specific point.

That is a short version of one of the ideas I play around with sometimes. I think time travel should be left to the experts like The Doctor and possibly the writers of Star Trek [img]/phpBB/images/smiles/icon_wink.gif[/img]

Hauteden

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"Okay, but what if, IF, I had some sort of retina in the future, but, it was only a "virtual" area shaped like a retina, and in some way, the photons are counted and measured, but go straight through? You could have a picture, right? And you wouldn't interact? Right?

Okay, I'm now certifiably insane, thanks to you, Nuttyimp!"

How do you count photons without them (or the detector) being affected? That violates all sorts of quantum principles and wouldn't work. Your insanity must be yet more ingenious, I'm afraid...

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My insanity could get more ingenious!

Tell you what, you build all that crazy stuff and tell me if it works or not!

At least I'm thoroughly crazy, not like those half-insane people. [img]/phpBB/images/smiles/icon_biggrin.gif[/img]

<font size=-1>[ This Message was edited by: Mr. X on 2001-11-21 10:22 ]</font>

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Unfortunately, as Joseph Heller conclusively demonstrated in "Catch 22", you can't be completely mad, Mr X., because if you were, you would of course assert that you weren't in the least bit crazy at all.

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Oh but I am not! I am a misunderstood genius! [img]/phpBB/images/smiles/icon_smile.gif[/img]

I'm only saying what your misguided brain has been telling you! [img]/phpBB/images/smiles/icon_biggrin.gif[/img]

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Not possible. The universe would not be stable if it were possible (as in the stability of it's own existance, and even in our infinitesimal time slice of personal observation, we can garner a lot of data of the universe's structure). Time is universal, but the measuirement of time varies a lot. The "speed of light" only holds true within the frame of the source.

Time travel defies entropy and conservation of energy.

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Time travel defies entropy and conservation of energy.
What if conservation of energy is merely an approximation, though, of a more fundamental law?

It's my understanding that time travel actually does happen, on a QM level--at least for short periods of time. I think most of the thread's point, however, is to contemplate time travel on the scale of humans--and, for that matter, to contemplate time travel into the past (the future isn't too hard, from a physics standpoint anyway)

30. ...the future isn't too hard...
Try not to! [img]/phpBB/images/smiles/icon_biggrin.gif[/img] I'm doing it right now. [img]/phpBB/images/smiles/icon_eek.gif[/img]

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