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Iam2004
2003-Dec-28, 11:44 PM
Now I really don't have any knowledge of physics so I don't understand the possibilties or the impossibilities. All I know is that it's a fasinating thing to think about!

It's a paradox either way I think about. On one hand I have common sense telling me that it is not possible and on the other that anything is possible. Who would have thought that there would be all this advance in technology that we have today? I know I may sound like a fool but I can't be the only one who thinks about this. What do you think? Is there anyone here with a knowledge of physics that thinks it is possible and can one day be accomplished?

TiMiX
2003-Dec-29, 12:59 AM
I don't think its possible, but you never know :)

How i see it is how can you make every atom jump back to where it was say 200 years ago?

You nor an atam has a faintest idea where it used to be 200 years ago, or even where it was just 2 seconds ago, as far as i can see the universe isn't recording any of this, theres no time scale out there to read as far as i can tell. But if there is, we haven't the fantest idea how to use it........... yet :blink: :)

damienpaul
2004-Jan-02, 12:55 PM
maybe there may be an application of the whole matter --> energy idea?

Littlemews
2004-Jan-03, 04:29 AM
There was a book that saids...you can use the wormhole as time machine...^_^ :lol: :lol:

lazserus
2004-Jan-03, 04:46 AM
Originally posted by Littlemews@Jan 2 2004, 10:29 PM
There was a book that saids...you can use the wormhole as time machine...^_^ :lol: :lol:
That seemed to be the easy solution for old science-fiction writers to get starships from one end of the galaxy to another. Well, after they realized that lightspeeds were impossible and even improbable.

TheThorn
2004-Jan-03, 06:04 AM
Sure time travel is possible. I do it all the time. Really. Every day.

So do you.

Forward.

At one hour per hour.

;)

trickster2020
2004-Jan-04, 07:38 AM
I Believe that TheThorn stated it the best.

damienpaul
2004-Jan-04, 12:18 PM
beautiful way of putting it thorn

TheThorn
2004-Jan-04, 04:20 PM
Hey <blush> Thanks, guys.

Actually, Special Relativity allows us to travel forward in time at rates higher than one hour per hour, simply by acheiving velocities near c. But I have a feeling that no one is going to consider it to be "real" time travel if there&#39;s no reverse gear.

damienpaul
2004-Jan-05, 11:47 AM
precisely

Planetwatcher
2004-Jan-05, 03:52 PM
I certainly hope it&#39;s not possible for real. At least not for humans.

That seemed to be the easy solution for old science-fiction writers to get starships from one end of the galaxy to another. Well, after they realized that lightspeeds were impossible and even improbable
As for what lazserus said, how true. I plan to use that in my novel inconjunction with a black hole. Not very real but makes a great story. ;)

damienpaul
2004-Jan-05, 11:48 PM
i plan to use it too, but in a totally different context...

jkmccrann
2005-Dec-27, 05:16 PM
I would speculate that time-travel is possible, of a sort, but unfortunately only in one direction, to the future!

Which is actually a good thing surely, for if it was possible to go back in time that could cause some really destabilising effects, and surely the proof of the impossibility of that, at least insofar as going back in time in the same time dimension, is the fact we don't have any visitors from the future. Were it really possible I don't think any amount of regulation would be able to stop it happening. I have heard it said somewhere that every hour we spend flying in the sky is worth perhaps a second or a minute or something of time travel into the future, and surely that is a pointer to as to how we can approach time-travel, as a means to extend our longevity.

:)

bigbluestar
2005-Dec-27, 07:35 PM
Mental experiments it is possible. Here is how you can do it. First you will need a vessel that can travel faster than light. the more the better. Lets use star trek terms to be universal. Go to warp Nine for an hour. Stop take a wicked telescope and view yourself 9 hours before your launch. The further and the faster you go. the more back in time you can see. Astronomers do it all the time they just do it without Saying "make it so"

Few rules.
1) You cannot go to the future. Past the firstlight to darkness
2) You cannot change the past, you can only record its photons.
3) If you decide to do it, don't tell my parents were I was on Jan 23 1998

cheers

Dragon Star
2005-Dec-27, 07:46 PM
I sure hope it's not, if a paradox was created...Poof....buh bye!

Tensor
2005-Dec-27, 07:49 PM
3) If you decide to do it, don't tell my parents were I was on Jan 23 1998

cheers

Oh, man. NOW you tell me. :doh: :lol:

trinitree88
2005-Dec-28, 03:43 AM
NO.:naughty:

bigbluestar
2005-Dec-28, 04:44 AM
NO.:naughty:
???

Dragon Star
2005-Dec-28, 05:07 AM
He was talking to Tensor

beskeptical
2005-Dec-28, 05:20 AM
We travel in time continually. And, research has shown that we can travel in time at different speeds relative to others or other objects.

While our ability to travel easily at different speeds is currently constrained by our technology, and while many very intelligent minds like Hawking have their more elaborate writings on the topic, I do think the facts I noted in my first two sentences above indicate there is some wiggle room. How much wiggle room and can one go in reverse is yet to be seen.

Another issue that must be considered is despite traveling through time at different speeds, are we still all in the same moment? When that person on the jet returns to Earth a fraction of a second ahead of, (therefore younger than), those that remained on the planet, the person is still, nonetheless, in the same moment as those persons which traveled at a different speed. This fact is rarely discussed in those interesting papers on time travel.

But I think it is the one issue that has the greatest impact on the subject. Are there multiple moments? Or are we all in the same moment? If there are multiple moments then are there multiple Universes?

Hawking's pool ball analogy depends on there being only one time stream. So an effect on the past changes the future. But an alternate scenario would be that an effect on the past changes one of many time streams. And then once you are out of sync with your time stream, can you return to it? If you return to it out of sync, will there be another you there?

So many questions, so little time to contemplate the Universe. Sigh.....

phunk
2005-Dec-28, 05:48 AM
In my opinion there is only one 'now', it just takes each of us a different amount of time to get from one now to the next. Has anyone found evidence yet if time is quantized or infinitely divisible?

astromark
2005-Dec-28, 07:04 AM
Does any one think time travel is posible? Well, of corse they do. I am not one of them. You can not change what has happened. Just as you can not alter what is to happen. As it has'ent happened yet has it. As for the nonsense about worm holes and black holes,. . No proof of any of this stuff being of any use to a space traveling ship. See what the Thorn said.

Hugo Drax
2005-Dec-28, 11:30 AM
I don't think anyone ends up in a different time frame to other people when they are affected by time dilation (whether on an aircraft or a near-c spacecraft); they have just aged less slowly than everyone else.

I tend to associate time with physical change (think of history as a film reel with a discrete frame every 5.391 × 10−44 seconds [Planck time]), which is why I don't believe reverse time travel is possible; you would have to (as others have said) find a way or returning every atom in the universe to wherever it was X amount of time ago.

You can travel forward in time, but (as TheThorn said) not by travelling directly from the present to the future (assuming they exist as seperate things - I don't think they do); you merely find somewhere (like a near-c spacecraft) where time happens at a slower rate than everywhere else. You could achieve the same result by going into (assuming such a thing is possible) suspended animation/stasis (Red Dwarf, Aliens etc.) for several hundred years.

(I think there would have to be multiple universes for past, present, and future states to exist simultaneously [you would "travel" in time by universe hopping]; that would solve the duplication of matter problem [the present is the past rearranged]; the need to rearrange all of the matter in the universe problem, and any causal paradoxes that you can think of)

five_distinct
2005-Dec-28, 04:54 PM
Does any one think time travel is posible? Well, of corse they do. I am not one of them. You can not change what has happened. Just as you can not alter what is to happen. As it has'ent happened yet has it. As for the nonsense about worm holes and black holes,. . No proof of any of this stuff being of any use to a space traveling ship. See what the Thorn said.

Unless you orbit really close to the event horizon for a while, and avoid anything that might want to hurt you on the way in.

But this leads me to wonder: To fat people age more slowly than skinny people? Health problems aside.

sidmel
2005-Dec-28, 06:44 PM
Interesting concept created by Kip Thorpe

http://www.zamandayolculuk.com/cetinbal/TimeMachine.htm

sidmel
2005-Dec-28, 07:19 PM
So if you take E=MC^2, do a bit of substitution and moving, you get t=md/√E

To make time negative, you just need to find some negative mass, negative distance or negative energy and control it, Bob's your uncle, but don't try to kill your grandpaw! :)

trinitree88
2005-Dec-28, 07:25 PM
???

Does anyone think that time travel is possible?

I was replying to the original post.....NO. I think it does not warrant much discussion. Simply ...NO.

beskeptical
2005-Dec-28, 08:30 PM
I don't think anyone ends up in a different time frame to other people when they are affected by time dilation (whether on an aircraft or a near-c spacecraft); they have just aged less slowly than everyone else.
....
you would have to (as others have said) find a way or returning every atom in the universe to wherever it was X amount of time ago.
....
You can travel forward in time, but (as TheThorn said) not by travelling directly from the present to the future (assuming they exist as seperate things - I don't think they do); you merely find somewhere (like a near-c spacecraft) where time happens at a slower rate than everywhere else. You could achieve the same result by going into (assuming such a thing is possible) suspended animation/stasis (Red Dwarf, Aliens etc.) for several hundred years......Very important points and an elaboration of what I was thinking.

While the person on the aircraft's relative time is slower, both the person on the ground and the one in the air are still in the same present moment at all times. This has profound implications as to whether the past and/or future exist.

We see the past light that is still traveling out from the source, but that doesn't mean the source still exists if one could merely out pace the light to reach it. Rather, it seems more likely should you out pace the light (and assuming you wouldn't just run into light from other sources) you would not find the future, you would find nothing.

It seems a romantic notion that the light which is passing us represents the existence of the past. But it doesn't. At least there is no evidence and no reason to think it does. The light exists, but the source is gone.

I think we have to go back to trying to understand the time dimension more precisely. There is a connection to that light which continues after the source is gone. Light travels in time but not everything else.

So many questions, so little time to contemplate the Universe. Sigh.....

beskeptical
2005-Dec-28, 08:51 PM
Interesting concept created by Kip Thorpe

http://www.zamandayolculuk.com/cetinbal/TimeMachine.htmfrom the story:
After 6 hours she turns the ship around and heads back to Earth which takes another 6 hours. After 12 hours have passed Kip will look through the wormhole still holding hands with Carolee and see that she has landed and is now out in the front yard. So he will let go and start toward the door to go out and greet her when he notices that she is not out there yet. The relativistic speeds and accelerations that she has encountered have dilated her time so that in Kip's view she is still out in space on her journey holding hands with him. So Kip waits for her arrival...he waits 10 years. When she finally arrives he goes out to greet her. He opens the door of the craft and finds her not having aged more than 12 hours since her departure with her hand still in the wormhole. He looks into the wormhole and sees himself 10 years ago holding hands with Carolee. The wormhole is now a time machine! Kip can step through the wormhole and go back as far as 10 years, to the creation of the time machine but not any earlier.Herein lies the question. While one person's time is dilated, are the two still in the same present moment?

Thorne is saying that looking through the worm hole, one sees time which appears to be passing at the same rate but outside of the worm hole, time is passing at a different rate. But that premise is flawed. Instead, through the wormhole, Kip looking in would see time passing very quickly. He wouldn't see it passing at the same rate as his. His wife would see time passing very slowly.

When the two ends of the worm hole reunited, while both would have experienced different amounts of time, they both would have traveled through the same 'distance' of the time dimension, stayed at the same present moment at all times and returned to the same present moment.

If that weren't the case, then how would they ever reach the same moment after separating? Would you just have to reach the approximate location within the three spatial dimensions? Why wouldn't any person flying in jets or space ships end up out of sync with each other in time?

Obviously Thorne thought this through in some way I am missing. Anyone know if Hawking or Thorne wrote about how when one returned to the location of the other, two people traveling at different rates in time ended up in the same time again?

beskeptical
2005-Dec-28, 09:08 PM
I e-mailed Kip Thorne. Should I be so fortunate as to receive an answer, I'll let you all know.

Here are some web lectures (http://www.its.caltech.edu/~kip/scripts/lectures.html) I found as well. This is so cool.

nokton
2005-Dec-28, 09:09 PM
Now I really don't have any knowledge of physics so I don't understand the possibilties or the impossibilities. All I know is that it's a fasinating thing to think about!

It's a paradox either way I think about. On one hand I have common sense telling me that it is not possible and on the other that anything is possible. Who would have thought that there would be all this advance in technology that we have today? I know I may sound like a fool but I can't be the only one who thinks about this. What do you think? Is there anyone here with a knowledge of physics that thinks it is possible and can one day be accomplished?
Why am I here?

five_distinct
2005-Dec-28, 09:26 PM
from the story:Herein lies the question. While one person's time is dilated, are the two still in the same present moment?

Thorne is saying that looking through the worm hole, one sees time which appears to be passing at the same rate but outside of the worm hole, time is passing at a different rate. But that premise is flawed. Instead, through the wormhole, Kip looking in would see time passing very quickly. He wouldn't see it passing at the same rate as his. His wife would see time passing very slowly.

When the two ends of the worm hole reunited, while both would have experienced different amounts of time, they both would have traveled through the same 'distance' of the time dimension, stayed at the same present moment at all times and returned to the same present moment.

If that weren't the case, then how would they ever reach the same moment after separating? Would you just have to reach the approximate location within the three spatial dimensions? Why wouldn't any person flying in jets or space ships end up out of sync with each other in time?

Obviously Thorne thought this through in some way I am missing. Anyone know if Hawking or Thorne wrote about how when one returned to the location of the other, two people traveling at different rates in time ended up in the same time again?

I think what you've said here is probably pretty accurate, though it would be interesting to hear Kip Thorne's thoughts....but actually you have it backwards. His wife would be seeing him age quickly, he would be seeing her move very slowly...and now that I think about it, the remake of The Time Machine shows this exact effect.

ZaphodBeeblebrox
2005-Dec-28, 09:43 PM
from the story:Herein lies the question. While one person's time is dilated, are the two still in the same present moment?

Thorne is saying that looking through the worm hole, one sees time which appears to be passing at the same rate but outside of the worm hole, time is passing at a different rate. But that premise is flawed. Instead, through the wormhole, Kip looking in would see time passing very quickly. He wouldn't see it passing at the same rate as his. His wife would see time passing very slowly.

When the two ends of the worm hole reunited, while both would have experienced different amounts of time, they both would have traveled through the same 'distance' of the time dimension, stayed at the same present moment at all times and returned to the same present moment.

If that weren't the case, then how would they ever reach the same moment after separating? Would you just have to reach the approximate location within the three spatial dimensions? Why wouldn't any person flying in jets or space ships end up out of sync with each other in time?

Obviously Thorne thought this through in some way I am missing. Anyone know if Hawking or Thorne wrote about how when one returned to the location of the other, two people traveling at different rates in time ended up in the same time again?
Here's, What you're Missing:

Everyone, Has their Own Personal Clock, Which Charts, their Own Personal, Passage through Time ...

When Time Is Dilated, This Clock Slows Down, Both With a Wormhole, Or Without, HOWEVER, The Difference Within, Thorne's Thought Experiment, Is This Difference, Is Made Explicit ...

In Other Words, By Having a, Real Time Link, With his Wife, The Man Is Bridging this Gap, And, Creating a Path, Between Points, on The Time-Line!!!

beskeptical
2005-Dec-28, 09:45 PM
I think what you've said here is probably pretty accurate, though it would be interesting to hear Kip Thorne's thoughts....but actually you have it backwards. His wife would be seeing him age quickly, he would be seeing her move very slowly...and now that I think about it, the remake of The Time Machine shows this exact effect.It was so confusing, I had to think about it and I still got it backwards. You're right. Darn, and that's what I put in the E-mail too. Oh well. ;)

bigbluestar
2005-Dec-28, 10:30 PM
thnx for the link beskeptical so appreciated

five_distinct
2005-Dec-28, 10:46 PM
Here's, What you're Missing:

Everyone, Has their Own Personal Clock, Which Charts, their Own Personal, Passage through Time ...

When Time Is Dilated, This Clock Slows Down, Both With a Wormhole, Or Without, HOWEVER, The Difference Within, Thorne's Thought Experiment, Is This Difference, Is Made Explicit ...

In Other Words, By Having a, Real Time Link, With his Wife, The Man Is Bridging this Gap, And, Creating a Path, Between Points, on The Time-Line!!!

I disagree. I think that, despite the fact that they're holding hands, he would still observe that his wife age much more slowly than he. And indeed, perhaps his hand, and maybe even he, would end up dying because of it (too much blood flow in, not enough out)...ignoring the biological ramifications of this, his hand would age more slowly than him too ;)

ZaphodBeeblebrox
2005-Dec-29, 06:33 AM
I disagree. I think that, despite the fact that they're holding hands, he would still observe that his wife age much more slowly than he. And indeed, perhaps his hand, and maybe even he, would end up dying because of it (too much blood flow in, not enough out)...ignoring the biological ramifications of this, his hand would age more slowly than him too ;)
Actually, I AGREE, With you ...

The Hand Holding, Is Just a Way, To Illustrate The Point, anyway ...

Next Person, I Meet, Who Wants, To Hold Hands, for 10 Years Straight, Will Be, The First!

beskeptical
2005-Dec-29, 10:35 PM
...
The Hand Holding, Is Just a Way, To Illustrate The Point, anyway ...

But the question is, is the point illustrated correct?

Chuck
2005-Dec-30, 02:12 PM
I don't think its possible, but you never know :)

How i see it is how can you make every atom jump back to where it was say 200 years ago?

You nor an atam has a faintest idea where it used to be 200 years ago, or even where it was just 2 seconds ago, as far as i can see the universe isn't recording any of this, theres no time scale out there to read as far as i can tell. But if there is, we haven't the fantest idea how to use it........... yet :blink: :)
You're not really putting atoms back to where they were 200 years ago. You're causing yourself to have existed when those atom are where they were 200 years ago. If you travel back 200 years then you were there 200 years ago. Nothing has changed.

beskeptical
2005-Dec-30, 08:38 PM
You're not really putting atoms back to where they were 200 years ago. You're causing yourself to have existed when those atom are where they were 200 years ago. If you travel back 200 years then you were there 200 years ago. Nothing has changed.
Wouldn't that mean your atoms have to all move in unison to a specific time? Where would the atoms go that your body had to move aside to fit?

The more I think about it, the fact one traveling at a different relative rate through time still ends up in the same time when returning to a place where others have traveled at a different relative rate has some implications that may not have been thoroughly considered.

If those atoms from the past are still there, how do you solve the problem of division of each moment? In other words, are the time increments in seconds?, hours?, half the speed of a light second? You have to have increments in order to visit one time and not still be in the other.

But let's think this through. Assume the light travels on and on but the source or the last thing it bounced off of does not still exist. If we traveled faster than the speed of light in one direction in space, we might be able to follow a light wave back in time by getting farther away from it's source.

After light leaves the source, the source continues on through time. Which means the light leaving the source is not older and older, it is newer and newer. We can get farther away faster than the light and wait for the light to reach us again. But we don't know if the light exists farther away. In fact, we have no evidence it does.

I think what's missing from our concept of the time dimension is the direction we are looking, while we see what something looked like in the past, is still forward time coming our way.

Forgive me for thinking out loud here but I think I just realized something I had backwards before. I had this concept that if we were looking at the past, if we traveled towards it, we'd be going back in time. But we have to travel away from it to go back in time, not toward it. If we go toward it, we are going forward in time. If we were to reach the object in view, we would reach it in present time, not past time, because as we went faster than light, we'd be reaching light that left the source more and more recently, not less recently.

I've been thinking this all wrong before. Am I the only one?

Chuck
2005-Dec-30, 10:28 PM
I don't understand the question about moving atoms aside. If I enter my time machine tomorrow and go back to 1805 then that trip is in my personal future but it's also in the global past. My atoms were already in 1805 taking up space like anyone else who existed in 1805.

beskeptical
2005-Dec-30, 11:09 PM
I don't understand the question about moving atoms aside. If I enter my time machine tomorrow and go back to 1805 then that trip is in my personal future but it's also in the global past. My atoms were already in 1805 taking up space like anyone else who existed in 1805.
That adds even more questions, what were your atoms doing in 1805? They would have been the same atoms as the ones that make up your body today. Would they disappear from the places they were? Would you be a duplicate so if you went back a few days would there be two of you? If you went back a few days would the past you disappear?

What I meant was the atoms that make up your body occupy physical space. If you went back to 1805, your atoms would have to occupy a space that was already occupied by other atoms.

Chuck
2005-Dec-30, 11:15 PM
If I go anywhere my atoms displace atoms that are already there at the time of my arrival.

beskeptical
2005-Dec-30, 11:31 PM
If I go anywhere my atoms displace atoms that are already there at the time of my arrival.Which is not physically possible giving what we know about the laws of physics.

Thorne was trying to give time travel theoretical plausibility, he wasn't trying to skip all the laws of physics.

I think the physics of matter (atoms as we have been discussing) wasn't thoroughly thought out in Thorne's scenario.

Chuck
2005-Dec-30, 11:37 PM
If I walk across a room the atoms of my body displace the atoms of the air that were previously across the room. That seems physically possible to me.

beskeptical
2005-Dec-31, 12:13 AM
If I walk across a room the atoms of my body displace the atoms of the air that were previously across the room. That seems physically possible to me.
Yes but those atoms and you exist in one Universe. If you were to add atoms to that Universe you would be breaking the laws of physics (unless a fixed amount of energy was exchanged to create the matter).

This is getting way off track. Go back to the post about how the atoms from the past couldn't rearrange themselves into their past positions and read through the posts again.

Chuck
2005-Dec-31, 12:32 AM
I read those posts. Atoms would not need to return to their past positions. My presence in the past would have occured in the past. My adventures in 1805 are already part of history. I don't remember them now because I don't start my time travel journey until tomorrow, but they've already happened.

eburacum45
2005-Dec-31, 06:31 AM
But that premise is flawed. Instead, through the wormhole, Kip looking in would see time passing very quickly. He wouldn't see it passing at the same rate as his. His wife would see time passing very slowly.
Why? They are looking at each other through the normal space in the middle of the hole; if you are suggesting that they are experiencing time at different rates then you are describing a different situation.
This situation you describe could occur if there is a strong gravity gradient through the hole; so it would be the same as if you were looking at someone further way from a black hole than you are.
If, for instance, the near end of the wormhole is more massive, you will get such a gravity gradient, and you will see the sort of time dilation you describe. If on the other hand the wormhole mouth at the far end is the more massive of the two, you will see the other end redshifted and the time dilation effect will be in the opposite direction, so the wormhole will be even more efficient as a time machine. Thorne is describing a situation where both mouths have equal mass, so the two ends experience time at comparable rates.

Ufonaut99
2006-Jan-03, 03:02 AM
It's worth noting that, in this case, Kip Thorne isn't keen on putting a bet on with Hawking (despite winning his previous one).

From some VERY small text atStephen Hawking: A Life in Science (http://www.nap.edu/books/0309084105/html/292.html)


Hawking’s chronology protection conjecture can be summed up, in its latest form, as saying that whenever any civilization, no matter how advanced, tries to build a time machine, by whatever means, just before the device starts to operate in time machine mode a beam of vacuum fluctuation radiation akin to Hawking Radiation will build up inside the machine and destroy it. Although Thorne agrees that “we cannot know for sure until physicists have fathomed in depth the laws of quantum gravity,” it is significant that on this occasion he refuses to place a bet against Hawking and says that “Hawking is likely to be right.”

ZaphodBeeblebrox
2006-Jan-05, 04:27 AM
But the question is, is the point illustrated correct?
Yes ...

As Eburacum said, Time For them, Will Pass Equally ...

I Was WRONG, Before!

As For The Atoms, If a Wormhole Is Used, As Per The Example; Then they Would Move Aside Naturally, As you Emerged Gradually, from The Hole!

astromark
2006-Jan-05, 07:09 AM
I have been watching this thread, and would like to sagest that to continually refer to time travel as if it were nothing more than distance traveled in time is as confusing as it looks when I wrote it. It will not be ever possible. For if it was to ever be possible would we not have met. This looks like the unmistakable truth.

ZaphodBeeblebrox
2006-Jan-05, 11:59 AM
I have been watching this thread, and would like to sagest that to continually refer to time travel as if it were nothing more than distance traveled in time is as confusing as it looks when I wrote it. It will not be ever possible. For if it was to ever be possible would we not have met. This looks like the unmistakable truth.
Why Not ...

We Move Through Time, ALL The Time ...

Trick Is, To Go The Other Way!

:think:

Chuck
2006-Jan-05, 01:58 PM
http://images.ucomics.com/comics/fa/2006/fa060105.jpg

Blob
2006-Jan-05, 07:49 PM
Hum,
Well, microscopic laws of physics are essentially time-reversal invariant, but macroscopic thermodynamics exhibits a profound time-asymmetry; so in the real world, entropy typically increases in closed systems.

A quick search on google of “Mach-Zehnder interferometer with feedback-loop” turned up this gem...

Quantum Theory Looks at Time Travel
Authors: Daniel M. Greenberger, Karl Svozil

Abstract:
We introduce a quantum mechanical model of time travel which includes two figurative beam splitters in order to induce feedback to earlier times. This leads to a unique solution to the paradox where one could kill one's grandfather in that once the future has unfolded, it cannot change the past, and so the past becomes deterministic.
On the other hand, looking forwards towards the future is completely probabilistic. This resolves the classical paradox in a philosophically satisfying manner.

"Quantum mechanics distinguishes between something that might happen and something that did happen. If we don't know your father is alive right now - if there is only a 90% chance that he is alive right now, then there is a chance that you can go back and kill him. But if you know he is alive, there is no chance you can kill him" - Professor Dan Greenberger.

http://arxiv.org/pdf/quant-ph/0506027

Layman Summery: technically backward time travel can happen but `destructive interference` cancels out all but one possible path into the past. So in real life it is ultimately not possible...

ZaphodBeeblebrox
2006-Jan-06, 01:29 AM
Hum,
Well, microscopic laws of physics are essentially time-reversal invariant, but macroscopic thermodynamics exhibits a profound time-asymmetry; so in the real world, entropy typically increases in closed systems.

A quick search on google of “Mach-Zehnder interferometer with feedback-loop” turned up this gem...

Quantum Theory Looks at Time Travel
Authors: Daniel M. Greenberger, Karl Svozil

Abstract:
We introduce a quantum mechanical model of time travel which includes two figurative beam splitters in order to induce feedback to earlier times. This leads to a unique solution to the paradox where one could kill one's grandfather in that once the future has unfolded, it cannot change the past, and so the past becomes deterministic.
On the other hand, looking forwards towards the future is completely probabilistic. This resolves the classical paradox in a philosophically satisfying manner.

"Quantum mechanics distinguishes between something that might happen and something that did happen. If we don't know your father is alive right now - if there is only a 90% chance that he is alive right now, then there is a chance that you can go back and kill him. But if you know he is alive, there is no chance you can kill him" - Professor Dan Greenberger.

http://arxiv.org/pdf/quant-ph/0506027

Layman Summery: technically backward time travel can happen but `destructive interference` cancels out all but one possible path into the past. So in real life it is ultimately not possible...
What I'd Like to See, Is an Experiment, In Which "Constructive Interference", Was Studied ...

In Other Words, an Experiment, In Which, The Time-Travel Event, Makes Itself MORE Likely, to Occur ...

Has Anyone, Done One of These?

Blob
2006-Jan-06, 06:36 AM
Hum,
Constructive/reinforced Interference is like moving forwards in time.... but it is determined ...?

beskeptical
2006-Jan-06, 12:35 PM
I'm still trying to think this through. We need a better understanding of the interaction between time and light waves.

Light waves begin their journey. If we traveled forward and backward along the wave, we'd be traveling in 3D space, not in time. When we got to the source, we'd have traveled toward present time. We'd get there when new light was being emitted, not when the past light left. Returning, we'd be reaching parts of the wave that were emitted in the past. But it's the light, not the past that we'd be encountering. When we got back to our starting point, we still be in present time.

Now consider the wave that left the source and has already passed us. That light should still exist. You could think once it passed present time, its existence ended. But that doesn't quite fit because the light existed yesterday when it passed other planets or galaxies before reaching here. On the other hand, that still only provides evidence the light wave existed in the past. It doesn't prove once the light reaches and passes present time that it continues.

I think the light continues to exist. I'm going to have to think about what that says about the time dimension and light. If the light that passed us still exists then past and future light exist. That doesn't mean past and future 3D space exists though. I think that's a big hurdle that even a wormhole cannot cross.

Blob
2006-Jan-06, 09:55 PM
We need a better understanding of the interaction between time and light waves.

Hum,
the problem here is i think your not treating the temporal dimension as a spatial.
And perhaps confusing this theory with the Wheeler Feynman theory.

(The Mach-Zehnder interferometer is not a time machine; It just show how destructive feedback cancelsout certain values)

Forget that there is a time dimension - the arrow of time will naturally emerge from the theory.
That is what is great about it.

In the Wheeler Feynman theory the particle you rightly say will travel through 3D space (but that space is really 4 d remember)...
So if it encounters another particle there is a `collision`....

So if it travels in the extra dimension then it can reach forward or backwards (in time) so it can collide with itself or another particle or bounce from the BB or not bounce from the open ended future, etc... (but this is best left to another thread)

ZaphodBeeblebrox
2006-Jan-07, 02:05 PM
Hum,
Constructive/reinforced Interference is like moving forwards in time.... but it is determined ...?
In Other Words, What If, an Experiment was Devised ...

In Which, While it Would Happen, Without it, The Outcome Becomes, MUCH More Likely, If a Time Travel Event, Occurs ...

Could It Be Done, And, If So, What Could it Tell us?

:think:

Candy
2006-Jan-07, 02:20 PM
http://images.ucomics.com/comics/fa/2006/fa060105.jpg
Where in the world did you find that? :lol:

Sticks
2006-Jan-07, 02:54 PM
As if to muddy the waters even further, in a sci fi story I once did, I used the concept of the Chronon (http://en.wikipedia.org/wiki/Chronon) as a hypothetical particle of time. (I know that does not fit the Wiki description of it as a mere unit of time). Now there was an idea that for every particle, there should be a corresponding anti-particle. (I think I heard that one from an episode of Space 1999 (http://en.wikipedia.org/wiki/Space_1999))

In my Sci fi story line, I did in the 1980's, I played around with Chronons, anti Chronons, accelorated Chronons and accellerated anti-Chronons to come up with a device that could either slow the universe down so you could appeare to move super fast or create a time machine that could send you back or forward, the only problem being that the device could not travel with you. So when the hero went back, he had to find the early experimental equipment he was later to develop as his device in order to get back, and rescue his friends from certain death in the past by bringing them into the present / future. As they were deemed dead in the past, killed by an exlosion that destroyed everything, the protection conjecture did not apply.

So getting back to the main thoughts here, what do we consider the Chronon to be, just a unit of measurement or a particle of time and if the latter, could their be a coresponding anti particle?

IIRC in the episode of Space 1999, the anti mattter universe ran backwards in time.

beskeptical
2006-Jan-07, 09:13 PM
Hum,
the problem here is i think your not treating the temporal dimension as a spatial.You are correct but that is my point. As I travel around looking at that light wave, I have frozen time and am traveling in 3D space. While I look at light that reached here from past time across the Universe, I am really still seeing present time light. It's an illusion that I am seeing past light. That past light not only traveled in 3D space, it also traveled in time. It is carrying a record of past time, but not actual past time.


In the Wheeler Feynman theory the particle you rightly say will travel through 3D space (but that space is really 4 d remember)...
So if it encounters another particle there is a `collision`....

So if it travels in the extra dimension then it can reach forward or backwards (in time) so it can collide with itself or another particle or bounce from the BB or not bounce from the open ended future, etc... (but this is best left to another thread)You lost me here.

Blob
2006-Jan-07, 10:25 PM
@Sticks
tnx,
I'll use the word Chronon for my answer to beskeptical .

@beskeptical
Hum,
while this is not really on topic...

You say you are travelling in 3D space, but i suggest that you are not.
You are indeed frozen in a `now` moment. There are however a whole line of `yous` stretching backwards and forwards in time, from your current position, in another hidden dimension (4D)

Now if you were to emit two Chronon particles. One Chronon particle will travel backwards in time while another will travel forwards in time. they can interact with you in the past and in the future...
And by interacting it creates two more Chronon particle ...and so on.

Normally there is an equal amount of Chronon particle moving backwards and forwards...EXCEPT, when a Chronon particle reaches the BB - it is reflected forwards .
With destructive interference we then end up with more Chronon particle moving forwards - This gives a direction to time.

The `Chronon particle` is just a normal photon.

A quick search of google of `Wheeler Feynman theory` will turn up a better worded explanation.

Chuck
2006-Jan-08, 12:43 AM
Where in the world did you find that? :lol:

Frank & Ernest (http://www.ucomics.com/frankandernest/2006/01/05). One of my favorite comic strips.

beskeptical
2006-Jan-08, 08:50 PM
...
@beskeptical
Hum,
while this is not really on topic...

You say you are travelling in 3D space, but i suggest that you are not.
You are indeed frozen in a `now` moment. There are however a whole line of `yous` stretching backwards and forwards in time, from your current position, in another hidden dimension (4D)But this is the issue, are there a bunch of mes? We have no evidence there is. We only have evidence that light from the past enters the present with memory of the past. Heck, so does video.

I think there is a bit of reasoning to think there isn't a whole bunch of mes. If two objects can travel at different speeds in time yet when they return to the same proximity of 3D space they return to the same present time. We know this because one aged at a different rate. Why wouldn't the person who slowed down return to a place in time that was before present time? If I put on the brakes on the highway and then return to my normal speed I find myself next to different cars. Unless I speed up faster than my regular speed I cannot return to my previous position.

The second issue I have with thinking there are lots of mes is how many are there? What is the division? Half a second? Half of half of a second? And so on? How small can those divisions of time be?

I don't understand the chronon thing and don't have time to read Feynman right now so I can't comment on that.

pasha582
2006-Jan-08, 09:25 PM
Now I really don't have any knowledge of physics so I don't understand the possibilties or the impossibilities. All I know is that it's a fasinating thing to think about!

It's a paradox either way I think about. On one hand I have common sense telling me that it is not possible and on the other that anything is possible. Who would have thought that there would be all this advance in technology that we have today? I know I may sound like a fool but I can't be the only one who thinks about this. What do you think? Is there anyone here with a knowledge of physics that thinks it is possible and can one day be accomplished?

We are all travelling into the future, so time travel is almost inevitable in that respect. You could slow down your rate of travel by, paradoxically, increasing your velocity. You can also slow down your forward "temporal" rate by approaching a massive black hole even horizon. Beware the tides!

To travel back in time you would need to restore the universe to the state at which it existed at that point in time. Put all the stars back, recollapse the super novas, "unrotate" spinning galaxies... The energy and information requirements would be considerable.

Maybe there is a way around that, but it is highly unlikely. It might be easier to travel to the "past" of a parallel universe, but there would not necessarily be any way of guaranteeing it's past was equivalent to ours. How does one choose among parallel universes, if they exist?

Skyywatcher
2006-Mar-15, 04:02 PM
Yes a neat thing to think about for sure but as far as we know it only goes one way, forward. So yes, time travel is possible but only in one direction. Until you die at least.

beskeptical
2006-Mar-15, 06:30 PM
Yes a neat thing to think about for sure but as far as we know it only goes one way, forward. So yes, time travel is possible but only in one direction. Until you die at least.My molecules will carry on for me after that.

Which brings me to a question (answer obvious but I was wondering how it fits in here).

The photons we see can have originated billions of years ago. They hold the record of the past but we see them in the present. All matter and energy were present in the Big Bang and remain the present today, though they can be converted from one to the other.

So just what would exist in the past? Everything would have to exist in the past, present and probably in the future as well, (since once one traveled back into the past the present would become the future and would hopefully still exist), at the same time.

I still wonder if we can experience time at relatively different speeds (proved) but we can't move in or out of present time. I don't agree with the Thorne/Hawking version that the person traveling close to the speed of light and experiencing time at a different speed is indeed in a different time.

So I'm going to take this to ATM and see what others think.

cosmic_notion
2006-Mar-16, 03:22 AM
OK think of it like this...time will spoil such things as food we know that....now if we freeze food it lasts much longer, we know that, and we know that the atoms are slowed down as the temperatures drop, so we know that we can deter time and slow it way down in some instances such as food preservation. Now if it were possible to do this with humans we could freeze ourselves and simply allow time to advance while we did not. So let me ask you htis....in the future do you think we will be ble to freeze man and revive man from this state???? I would say YES! So there is your answer!

Wina
2006-Mar-16, 04:08 AM
I'll admit to my personal belief in there being the possibility of travel through time, on the other hand I'll state that I sure as **** don't know how to do it and neither do you. However, for the sake of argument, there are certain plausible methods that could definitely be used convincingly in science fiction (at least the way I see it).

1) If you were magically able to record the exact position and motion of every single atom within the affected region (I say affected region because there's no reason to alter time within the entire universe or even solar system if you just want to do it on Earth. And then somehow (also magically) able to return every single atom to those prior states simultaneously. This would unfortunately have the side effect of killing and giving life to billions upon billions of life forms depending on the size of your affected region.

2) You completely and totally bend the dimensions (first second third and fourth) of the natural universe into a pretzel, point and laugh at them, and finally spin them around 180 degrees until they throw up from motion sickness.

3) As a last and final thought, you would exclude yourself and whatever device you used to achieve this state, from the natural universe entirely, wave at it from the other side of the one way glass, again point and laugh at it, and finally move yourself around to wherever you wished to (by playing supreme deity with the physics of the universe) as you reintegrate yourself with the universe you just worked so hard to escape. (Why are you going back you freak! /slap)

And of course the problem with all of these scenarios is the fact that either you yourself would be affected by such means and cease to exist by switching your device on (there are theories to the effect that this has already been done) or simply by existing in the past where the molecules that compose you already exist and you wind up with an odd paradox which could have unknown effects. I personally find it gruesome and hilarious to hope that such a situation would result in the same explosive devastation that arises from matter and anti-matter coming into contact with one another.

teehee, have fun Authors and dreamer!

clop
2006-Mar-16, 06:10 AM
Hello.

I clearly remember that several years ago I read a paper about a particle collision experiment that produced short-lived particles which seemed to travel backwards in time.

Unlike normal particles, which appear after collisions and move away from the impact and decay within a tiny fraction of a second, these particles would appear out of nowhere a tiny fraction of a second before the collision and move towards the impact and disappear at the time of the collision. The time between the appearance of these strange particles and the collision was about the same as the decay time of a normal particle. The strange particles did not appear unless a collision took place later on.

Does anyone have a link to this experiment?

clop

astromark
2006-Mar-16, 08:11 AM
I to would like to know more about this experiment. . . any body ?
but no. Its science fiction to think we will ever affect time travel. We may and could at some future date master the cryogenics for life preservation into the future of a long space journey., but you are not testing that on me. . . .

Ufonaut99
2006-Mar-16, 10:29 AM
OK think of it like this...time will spoil such things as food we know that....now if we freeze food it lasts much longer, we know that, and we know that the atoms are slowed down as the temperatures drop, so we know that we can deter time and slow it way down in some instances such as food preservation.

Question: What makes food go bad? Answer: All the bacteria, fungi, and other greedy critters that guzzle the food before you can get to it.

When it gets REALLY cold, most creatures crawl into a corner and wait it out. What they don't tend to do is pig out on a nice cold salad. Same goes for all those greedy guzzlers.

The upshot is that freezing doesn't send the slab of meat on a time travel - we're simply messing with the appetites of the microscopic feeders.


Now if it were possible to do this with humans we could freeze ourselves and simply allow time to advance while we did not. So let me ask you htis....in the future do you think we will be ble to freeze man and revive man from this state???? I would say YES! So there is your answer!
I would say NO!
There's one big problem with freezing people and then reviving them.
Every cell in our body is filled with water. Unlike most liquids, when you freeze water, it EXPANDS rather than contracts (which is why icebergs float instead of sink).
This means that, when you freeze a body, the water in the cells expand - which mean an awful lot of cells go POP ! Not good news when the unfortunate freezee gets thawed out.

Ufonaut99
2006-Mar-16, 12:12 PM
I clearly remember that several years ago I read a paper about a particle collision experiment that produced short-lived particles which seemed to travel backwards in time.


You could be thinking of particle-antiparticle annihilation. Feynman originally conjectured that anti-particles are simply particles travelling backwards in time.

For example, imagine an electron and positron annihilating, resulting in photon shooting off. This could equally well be imagined as an electron firing off a photon, with the recoil resulting in it being kicked backwards in time (while those of us travelling forward in time would see its charge reversed - ie. as a positron).

I believe the story goes that a young Feynman once bragged to his professor (Wheeler IIRC) that he knew why all electrons have exactly the same mass and charge. "Because it's all the same electron!" was his explanation. When Wheeler asked where all the positrons were, Feynman replied "maybe they're all hidden in protons". I don't think he held that opinion for too long, but it shows his mark of greatness in combining creativity and boldness.

Anyhow, you can see this (http://en.wikipedia.org/wiki/Antiparticles#The_Feynman-Stueckelberg_interpretation) and that (http://www.frerichs.net/feyn.html)