Time travel

[Absane]

I have not read much of this thread... however..

I seen on TV (Discovery Channel or TLC) that it could be possible that people are traveling backward in time, however we do not see them coming here because either the universe will not allow them to affect the past in any way... or that they are going back into some parallel universe... way too many that the odds we will see them are very very very very slim... I guess this would help elimate the problem of the paradox. Like, I could go back into time and kill hitler, go back into time and see he was never murdered...

 

[Nasor]

Originally posted by doom
Paradoxes are a non issue if the many worlds interpretation of quantum mechanics is correct and theres good evidence to suggest thats the case,thats how things work,though not for certain yet.
In this way we can go back in time because backwards is like a hall of mirrors while forward is just one mirror if you catch my drift.

The 'many worlds' interpretation really isn't that popular among serious physicists. I'm not aware of any aspects of quantum physics that can't be explained by the orthodox 'indeterminate wave function' explanation for quantum phenomena without having to resort of the many worlds explanation.

 

[Barionix]

Paraloxes

In the hypothesis of the multiverse the situation is more or less the same,because if is true that any traveller won t suffer the consecuences of his/hers acts in his own universe is also the fact that another "copy" of himself can come from other universe and kill his(the first traveller s )grandparents,and again the question:If the traveller is here that didn t happen but if so....(ad infinitum);and in an infinity of potential paralell universes there would be infinite travellers coming and going to any point of the multiversal branes,that would be a lot of "overimprinting" of travelers from "anyverse"...


The possibility to go back within the same universe and not being detected sounds good,but how could you see or hear anything witouth interfering the photons and the air pressure waves,or walk without pressing the floor,etc...


And besides,how would the traveller be going backwards in time as the same time he goes forward;I mean his very body,and machine;for if it is travelling(the ship), backwards in time, is also some time running forward for it,for if not the very moment it departs to the past,would be put to the moment prior to the activation and...as the unprevented traveller won t have any recall of having turned it on,so he would be trapped in a perpetual loop...

 

[wayne_92587]

Los Angeles Times ,Tues. Nov. 16,1999
Page 1 column 1
TIME,SPACE OBSOLETE IN NEW VIEW OF UNIVERSE
"The history of physics," says Harvard physicist Andrew Strominger, " is the history of giving up cherished ideas."
No idea has been harder to give up, however-for physicists and lay people alike- the everyday notions of space and time, the fundamental "where" and "when" of the universe and everything in it.
Quantum mechanical understanding of the atom revealed that space and time are inherently jittery and uncertain.
Now, some physicists are taking this revolutionary line of thinking one step further: if their theories are right, in the words of Edward Written of the Institute for Advanced Study in Princeton, space and time may be "doomed."
Concurs physicist Nathan Seiberg, also of the institute: " I am almost certain that space and time are illusions.

 

[doom]

As this thread is about time travel,i thought you may want to watch a program,or rather a lecture by prof.paul davies,talking about wormholes and time travel and stuff,most youll know if you read his book,
youll need real player (free download available at www.real.com):



http://www.hpc.susx.ac.uk/~vega/streams/vpl/d2.ram

 

[Barionix]

I ve read,and watched on TV some of the theory of Paul Davies about wormholes ,but how does he deal with what Stephen W. Hawking noticed, the informational paradox that arises even in a deterministic consideration of time travel(ie if only would be "allowed"travels that do not contradict the causality chain(,as the grandfather paradox,the killing Hitler one,etc),so everything that the traveler "modifies",implies his presence in the past,in a closed loop);but where did the information that the mere presence of the traveler implies,I mean, if he meets somebody in the past and gives her a text that will allow the discovery of timetravel...where did the information came from?...

 

[doom]

Originally posted by Barionix
I ve read,and watched on TV some of the theory of Paul Davies about wormholes ,but how does he deal with what Stephen W. Hawking noticed, the informational paradox that arises even in a deterministic consideration of time travel(ie if only would be "allowed"travels that do not contradict the causality chain(,as the grandfather paradox,the killing Hitler one,etc),so everything that the traveler "modifies",implies his presence in the past,in a closed loop);but where did the information that the mere presence of the traveler implies,I mean, if he meets somebody in the past and gives her a text that will allow the discovery of timetravel...where did the information came from?...

Well watch the lecture and youll find out

 

[Zero Mass]

In the book Slaughterhouse Five by Kurt Vonnegut, the author wrote about a species of aliens called Tralfamadorians that exist in the 4th dimension differently than Humans do. A Tralfamadorian is cognizant of all moment of his or her life, and can experience them in any order, none at all, all at once, or anywhere in between. This thoery of time is that everything that has happened, is happening, or will happen has already happened and already exists. So time is like one big loop where everything has happened and is happening simultaneously.

Einstein believed that time travel was possible because he observed and theorized that time could be relative like gravity when he pointed out that space-time could be bent. So if space-time could be bent by something lie a large source of gravity (the sun for instance) then is it not possible for a object of greater mass, say a black hole which is infinitely massive, to break and perhaps alter our concept of time?
I don't know, sounds like science fiction mumbo-jumbo if you ask me.

ZERO MASS

 

[errandir]

Originally posted by Zero Mass
In the book Slaughterhouse Five by Kurt Vonnegut, the author wrote about a species of aliens called Tralfamadorians that exist in the 4th dimension differently than Humans do. A Tralfamadorian is cognizant of all moment of his or her life, and can experience them in any order, none at all, all at once, or anywhere in between. This thoery of time is that everything that has happened, is happening, or will happen has already happened and already exists. So time is like one big loop where everything has happened and is happening simultaneously.

In order for them to "experience" I'm assuming the necessity of conciousness. No one knows how to describe conciousness, physically or otherwise, but I suspect that yet another dimension would be required to prevent stasis.

Originally posted by Zero Mass
Einstein believed that time travel was possible because he observed and theorized that time could be relative like gravity when he pointed out that space-time could be bent. So if space-time could be bent by something lie a large source of gravity (the sun for instance) then is it not possible for a object of greater mass, say a black hole which is infinitely massive, to break and perhaps alter our concept of time?

I don't recall learning about this one of Einstein's opinions, but, anyway, I think that time is being confused with conciousness. There is time, and then there is proper time, both defined within the framework of relativity. What I'm not clear on here, is whether we're talking about "Back to the Future" type time travel or "Time Machine" time time travel. It seems that the latter is far more plausible and consistent with relativity. Though, I don't believe that time travel (reverse, anyway) is at all possible without appealing to the principles that are specific to quantum mechanics.

 

[errandir]

Originally posted by doom
Oh relativity allows forward travel,without a doubt,your second paragraph is about right,you leave earth torwards the speed of light and youll only age (or time will pass for you slower relative to earth) maybe a year,youll get back and 20 years might have passed.

In this traveling, the envirnment remains a continuum, and it is much different than the flashy hollywood type time travel.

Originally posted by doom
Basically paradoxes would only be the case if you dont believe the many worlds interpretation of quantum physics,i think at a quantum level either way time travel shouldnt be an issue but in classical terms its a worry incase people go and kill there granfather before his grandpa had sex with grandma,bit of a key problem,although its NOT a physics problem with time travel,its a logical problem.

This is very much a physics problem if you believe in the basic physical principle of causality (which is not directly obeyed in the basic level of quantum mechanics that I've studied). I think an easier example (physically) is the time traveling billiard ball. It travels into the "portal" (let's say into the past), and it comes out, hits a wall, bounces back, and then hits ITSELF! Uh oh, how does it go into the portal? If we required a causal system, well then this WOULD be a problem, but QM politely speaks up, "Ehem. Excuse me, but the particle is actually a wave function (exists in a multiverse). One projection was prevented from going through the portal, but it is actually a superposition of other projections. One of these DID go through the portal, thus, no paradox." (See the double slit experiment.) Of course, there is a problem with this, in that, upon striking itself, there was a collapse. I'll have to give it some thought to reconcile.

 

[errandir]

Originally posted by doom
Ive always hated his argument which suggests some force destroys your time machine when you want to go backwards,theres no call for you to reason that at all,also im uncomfortable of the GOD exists overtones,anyone who mildly believes in god is likely to fudge stuff to suit there personal bias,this is one of those examples.

How does a belief in God inhibit consideration of time travel? Is time travel believed to be evil or something?

 

[errandir]

Originally posted by jjhlk
Any thoughts of time travel just seem to be from people finding loop-holes in the laws of physics - no doubt due to something we don't understand yet (in reference to wormholes specifically).

The field of quantum mechanics is a good example of entertaining loopholes.

 

[errandir]

Originally posted by kajolishot
Surely the fourth dimenstion does not have to be time itself.....it could (though less likely) be another spatial dimention normal to our three dimensions.

"The" fourth dimension, as if it has a name? Is that like saying "the" first dimension is strictly height, "the" second is strictly width, and "the" third depth? If you are looking down from above, then are you looking at the world sideways?

Of course one could define "the" fourth dimension however one wanted to; it is arbitrary. It doesn't even have to be metrical, but, for relativistic purposes, one needs at least 4 metrical dimensions. In quantum mechanics, in simple models, there are 3 x infinity dimensions, none of them metrical. Also, it may be instructive to point out that most treatments of relativity distinguish "time" as the zeroth dimension.

 

[errandir]

Originally posted by Nasor
The 'many worlds' interpretation really isn't that popular among serious physicists. I'm not aware of any aspects of quantum physics that can't be explained by the orthodox 'indeterminate wave function' explanation for quantum phenomena without having to resort of the many worlds explanation.

I'm not aware of any generally accepted "explanation" of quantum mechanics, but I appologize if I have misunderstood you. The generally accepted working model declares a wave function, the kinetics of which are governed by Schoedinger's equation. This is quite unsettling, though, for several reasons, not the least of which being the lack of determinism.

There are interpretations, but I don't know of any that really "explain" quantum mechanics. The one that I think gets the closest is the Bohm-deBroglie interpretation. It attributes to the particle in question a classical trajectory, but also appeals to "mystical" quantum forces. The interpretation to which most reference is given is the Copenhagen school, to which I believe you refer. This poses no "explanation" whatsoever, only a mechanism for predicting results.

 

[errandir]

Re: Paraloxes

Originally posted by Barionix
In the hypothesis of the multiverse the situation is more or less the same,because if is true that any traveller won t suffer the consecuences of his/hers acts in his own universe is also the fact that another "copy" of himself can come from other universe and kill his(the first traveller s )grandparents,and again the question:If the traveller is here that didn t happen but if so....(ad infinitum);and in an infinity of potential paralell universes there would be infinite travellers coming and going to any point of the multiversal branes,that would be a lot of "overimprinting" of travelers from "anyverse"...

Good point. I think the key is the path that a traveler would be able to take on the multiverse tree. I think that the most logically feasable path for reverse travel would be that path representating the current line of conciousness. Once the traveler arrived at the destination, the arrival itself would shift the branch of the traveler's conciousness. Only after this point will the traveler now have left the previous reality/conciousness. Never after will the traveler be able to return to the original branch, because the event of the traveler appearing at that point in time does not exist in the original branch. That is not to say that nothing will ever again be familiar, but it is probably unlikely due to the deterministic chaos (butterflies causing hurricanes, etc.).

Basically, the traveler's worldline would just disappear in the original reality (it would not merely break, and the broken end fall further down the tree, overlapping along a portion.). Effectively, the traveler would cease to exist. In a higher dimensional view (several infinities), the worldline would curve back to a point and osculate itself at the event of the traveler's appearence in the past. From that point, the worldline would go off in a different direction since the traveler contains fermions.

Originally posted by Barionix
The possibility to go back within the same universe and not being detected sounds good,but how could you see or hear anything witouth interfering the photons and the air pressure waves,or walk without pressing the floor,etc...

Another good point.

Originally posted by Barionix
And besides,how would the traveller be going backwards in time as the same time he goes forward;I mean his very body,and machine;for if it is travelling(the ship), backwards in time, is also some time running forward for it,for if not the very moment it departs to the past,would be put to the moment prior to the activation and...as the unprevented traveller won t have any recall of having turned it on,so he would be trapped in a perpetual loop...

Another very subtle but excellent point. In practice, if we were to try to implement such a device, I suspect a huge possibility for this problem to occur. It seems that, if we get the machine almost right, but haven't worked out the bugs, then this will happen. I think there was some episode of "The Outer Limits" or something that had a machine built by the military. I only caught the last few minutes, but it was an interesting proposed scenario. Some guy, I suppose, was present at the site when the device was tested, and he tried to shut it down. As a side effect, he got sent into the past, and continued his timeline up until the event of the malfunction, at which point he was sent back into the past again, but to a less extent. You can see that, if this consequence were not alleviated, eventually he would get stuck in an infinitesimal time loop (and possibly eventual annihilation, if he's lucky), while the rest of the world went on its way. Of course, the bad guy got stuck holding the bag, Yeah happy endings.

 

[errandir]

Originally posted by Barionix
I ve read,and watched on TV some of the theory of Paul Davies about wormholes ,but how does he deal with what Stephen W. Hawking noticed, the informational paradox that arises even in a deterministic consideration of time travel(ie if only would be "allowed"travels that do not contradict the causality chain(,as the grandfather paradox,the killing Hitler one,etc),so everything that the traveler "modifies",implies his presence in the past,in a closed loop);but where did the information that the mere presence of the traveler implies,I mean, if he meets somebody in the past and gives her a text that will allow the discovery of timetravel...where did the information came from?...

Where did the universe come from?

 

[wayne_92587]

Originally posted by errandir
Where did the universe come from?

From hither and thither; in the beginning, before the moment of inertia, at a uncertain moment, point, in Time and Space, before time began, Singularities were here and there, roundabout, alone in the Emptiness without momentum, uncertain, without meaning, without cause.

 

[errandir]

It was a rhetorical question. I would like to hear what Barionox has to say about it though, since he seems to have a problem with the origination of something from nothing. Quite frankly, I am troubled by this idea myself, and I don't find your explanation very helpful.

 

[Zero Mass]

I am not talking about Michael J. Fox flux-capictator type time travel. Einsteins theory of relativity touches on how both light and time can be bent due to a extreme force like gravity. I was just wondering that if the fourth dimension can be relative, then can it be tampered with in any way?
The example about the sun I wrote of is how Einstein, among many scientists, have noticed that the images of stars right behind the sun are actually bent light images from stars in other positions. The same kind of effect applies to space-time. As the sun with its large gravitational field sits in space time, it creates a bend or a popcket within it due to its gravity. And the application of this idea is all very theoretical, but if there is an infinitely massive object (a black hole) then wouldn't it be possible to have a tear in space-time that could possibly completely alter what we consider linear time?

ZERO MASS

 

[errandir]

Originally posted by Zero Mass
I am not talking about Michael J. Fox flux-capictator type time travel.

In that case, there is nothing special about time travel, and it happens all the time. I am traveling through time right now. Every second that goes by, I have traveled one second through time. This is different for different observers, and that is the reason for the interest, I think. But, for special relativity anyway, there is only provision for traveling into the future, in the sense that, your proper time can never have an oposite sign to the coordinate time in any reference frame.

Originally posted by Zero Mass
Einsteins theory of relativity touches on how both light and time can be bent due to a extreme force like gravity.

This is a bit vague. What do you mean by "light and time can be bent?" I'm assuming that you mean space-time can be bent, and that, as a result, the path that light takes appears, to us, to bend. As far as time being bent all by itself, I don't think that is what Einstein meant, and I don't think that it even makes sense to say.

The only force that we know to exhibit this bending effect, Einstein declared was not actually a force. That is one of the things that general relativity gives us. Gravity is the curvature of space-time; the gravitational field is the measure of that curvature, and the mass-energy tensor is responsible for the curvature (it is the source of gravity). Gravity is not an extreme force; it is the weakest "force" (as far as its effect on matter compared to the effect of the other forces). The gravitational force IS longrange, if that's what you mean, but not comparatively strong. Also, the existence of any arbitrarily small amount of gravity, by definition, will curve spacetime, so "extreme" should be sticken from the requirement.

edit:
(I guess extreme could also mean extremely small. I'm sorry if that's what you meant.)

Originally posted by Zero Mass
I was just wondering that if the fourth dimension can be relative, then can it be tampered with in any way?

The fourth dimension is not relative, only what we attribute to it. Of course, it is widely accepted that the attribution can be "tampered with." That is precisely what happens in relativity that makes it different than Newtonian mechanics.

Originally posted by Zero Mass
The example about the sun I wrote of is how Einstein, among many scientists, have noticed that the images of stars right behind the sun are actually bent light images from stars in other positions.

Other positions? Is there some conflict? How would you define "position?" There is a meaningful definition that position is determined by the angle that rays of light from the stars make to each other at the position. This is called astrogator's coordinates. The contradiction to which you refer is probably the previous notion that light travels in straight lines through space vs. the notion that the world line of a light ray is a geodesic.

edit:
(...which is to say: a curve of relative minimum proper length in space-time)

Originally posted by Zero Mass
The same kind of effect applies to space-time.

It is not the same KIND of effect; it is the SAME effect. Your first wording was inaccurate. Light always follows a geodesic, it does not bend in space-time. Space-time bends, so the topology (the connectivity of events by means of light) seems to manifest in the curvature of the light rays.

Originally posted by Zero Mass
...if there is an infinitely massive object (a black hole) then wouldn't it be possible to have a tear in space-time that could possibly completely alter what we consider linear time?

A black hole is NOT infinitely massive; some would say that the matter inside the black hole is infinitely DENSE. It is well known that a black hole is a tear in space-time, in the sense that space-time does not exist "inside" a black hole (especially not at the singularity, but, to an outside observer, there is some boundary beyond which the observable universe ends). What concept of linear time? What do you mean by linear?