Is time travel possible theoretically ?

Samus,

In general, I agree -- but go and try to tell that to quantum physicists or to relativists...

As for your assertion that one can prove anything with math, I'm afraid your are confusing the flabby drawl presented as math in the "theomatics" circles, and the rigid, axiomatic derivations employed in physics. Certaily, there are always assumptions embedded in any axyom; but in the case of phycics, those assumptions are often a result of measurement, or give rise to theories that feature amazing accuracy when their predictions are verified empirically. That means the model is not arbitrary, but indeed represents something very concrete and relevant about the world. Remember, black holes used to be just a crazy idea until recently -- and where did they come from? -- from the very same theory that is predicting wormholes.

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I am; therefore I think.

 

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ok, after some reflection on GR (what some meditation sometimes can do

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) I have come to the conclusion that wormholes actually don't violate the equivalence principle of GR.
The question in GR is not am I time deleted or not, this is simply an effect due to transformation of coördinates. The question is : are the laws of physics the same for all observers, or in other words is there such a thing as a preferred reference system.
What we have at the mouth of a wormhole is 'simply' some deformed topology of spacetime. This deformation makes measurements of the surroundings path-dependent, this means measuring lightsignals is dependent of how the signals travel from their origan to your measuring device. This is also true in 'normal' space since for example light from stars gets bent when we observe the stars close to our sun (during a solar eclips for example). We could also ask ourselves where is the star really, this however is not a question addressed by GR.
So the question is there timedelation or not is mute, it all depends on through wich topology you are making your measurments : no paradox.

However something else troubles me a lot more and that are the conservation laws of energy and momentum. Suppose you have two mouths with a relative speed V, when I step trough a mouth my energy as opposed to my starting point has just increased with MV^2/2 with M my mass. Where does this energy come from ?

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"If I have been able to see further, it was only because I stood on the shoulders of giants."
Isaac Newton

 

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Is it perhaps possible we (humans, life) can exist in lots of different histories at one time and that when people claim to see ghost that this in fact a glitch in the time continum and we are in fact looking at another history existing at the same time, if not instead of the present one?

 

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Are wormholes similar to the coriolus effect

 

Hi Epitectus,

No, they are not similar; in fact, they are two completely different things.

The coriolis effect is caused by the rotation of the earth, and its consequence is that free moving objects (eg. clouds or a cannonball) get bent away from their straight path in a direction that depends on the initial way they were going and on what hemisphere you're on.

Wormholes are "bridges" in the spacetime continuum (Einstein predicted that the spacetime continuum gets bent when mass is present. With some imagination you can think two masses can bend spacetime that heavily, that the "dips" merge together - it's quite difficult to imagine that in 4 dimensions). They have not been observed in real life though: their existance is a theoretical consequence of the equations of general relativity from Einstein.

Bye!

Crisp

 

Plato,

You asked:

"Suppose you have two mouths with a relative speed V, when I step trough a mouth my energy as opposed to my starting point has just increased with MV^2/2 with M my mass. Where does this energy come from ?"

Well wouldn't the extra energy be from the "moving" mouth which you just stepped into. I see no difference in this to say standing still, then being taken by a chairlift on a snow field. Obviously in the real world you wouldn't be able to step into the mouth instantaneously, hence you would need to match the speed of the mouth first, which requires adding energy on your behalf.

 

Rambler,

there is a huge difference between the chairlift and the wormhole. In the chairlift you are staying in the same spacetime continuum, going through the wormhole is actually going inside a new spacetime continuum.
You see, the mouths are moving with respect to each other only through normal space but through their wormhole space they are standing perfectly still.
So if you are going through the wormhole no laws are violated through wormhole space but they are violated through normal space because in normal space you first had no kinetic energy and next you have suddenly an energy difference compared to where you left. There is no matching of speed involved because the mouths aren't moving through wormhole space.
Hence the paradox of course...

Honesty obliges me to say that my view on wormholes and time travel has changed since I first started this thread. If people have been following the discussions in the determinism vs. indeterminism thread they will know what I'm talking about.
I am now convinced that the equations of Einstein are in need of revision. The time symmetric aspect needs to be taken out. There are already people trying to do this very thing, some work is being done in the Texan Prigogine institute but this is all very cutting edge theory and to draw any conclusions now would be precausious, to say the least.
What I can say is that time travel won't work any more in the revised equations because there will be a distinct arrow of time emerging from the basic equations themselves. This means that everything is compelled to go in this one direction : from past to future, no turning back !

Miss Happy,

This would also do away with the notion of parallel dimensions I'm afraid. They were a concoction of people trying to explain the wave nature of quantum mechanics and strange things like the same particle going through two slits at once and thereby creating a diffraction pattern. Quantum theory also has the same lack as relativity : namely the time symmetrie in the equations. If you take the probabilities themselves as basic stuff and let the wave functions drop, this takes away all need for parallel dimensions.

This is actually a good thing because if you think about it, an infinite amound of parallel dimensions would mean an infinite amount of Plato's trying to explain something to an infinite amount of Miss Happy's, where is the real you ? This idea was crazy in the first place so I think it is best we can put it to rest now...

So in answer to my previous question that started the thread :
Is time travel possible theoretically ?
I would have to say : Yes, but only in one direction : forward !

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I err, therefore I exist !

 

Plato,

Ok you have said that there would be 2 different space-time continuum. Wouldn't that mean then for your comparison you would need to look at the system with 2 different refernece frames? And hence to do an accurate comparison of kinetic energies you would need to do some kind of "mapping" of the velocities as seen from each respective reference?

Here is what I see happening. Our guinea pig is standing in normal space watching a wormhole mouth zip past at velocity V(m)(for mouth) for the guinea pig to enter the mouth it needs to match the velocity of the mouth...i.e. raise its kinetic energy. Now conversly if the the guinea pig is inside the mouth the refernce frame its in tells it it has no kinetic energy, however the moment it exits the wormholes space-time, its transformed its refernce frame and sees that the extra energy it appears to have gained is a result of taking some of the energy the WHOLE wormhole system had... with it, and was oblivious to because of the reference it was in. Analogous to the velocity of a ball bouncing inside a train as seen by an observer inside the train, and by one outide the train.

Sorry to bug you on this Plato, you no doubt realise that I only read this stuff out of interest, my only formal training was from the perspective of an electronics engineer...so I had a limited study of quantum mechanics and even less relativity. As you can appreciate engineers only look at the stuff relevant to their work and how it can be exoploited..we never looked at it as a subject on its own.

 

Rambler,

actually I'm streching the word 'different' here cause 2 different space-time contiua would mean there is a discontinuity between them in order to make a distinction. This however is not the case because the mouth is not a discontinuity but a rather continuus change of the 'flat' geometry of normal space to the wierd folded geometry of the wormhole space. The difference lies in the geometry.

The guinea pig that watches a wormhole mouth zip by would be standing next to the other mouth that is at rest with respect to the guinea pig (that is my set up). Looking through the other mouth the zipping mouth stands perfectly still.
However your Whole wormhole system energy got me thinking : what happens to the internal geometry of the wormhole if the mouths move against each other ? It changes of course, this change must also take energy so perhaps going through a wormhole also involves an energy transfer. Where does all this energy come from ? From the mouths of course because that is the only connection the wormhole has with the universe. So I guess towing along a wormhole is not that easy as I first thought

Don't sweat it about bugging me about these things. Asking things always works both ways, the asker and the ask usually learn something out of it.

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I err, therefore I exist !

[This message has been edited by Plato (edited May 26, 2000).]

 

According to Einstiens Theory of Relativity, time travel_is_possible.

(apparently) As you near the speed of light time slows down. So, say, travel to Wolf 339 at 98% the speed of light. Time will travel (for memory) 14% slower than on earth. Leave in 2050 and when you come back in 2065 you would only have aged around 13 years.

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"The credit belongs to the man who is actually in the arena, whose face is marred with sweat and dust and blood; who strives valiantly; who errs and comes short again and again; who knows the great enthusiasms, the great devotions, and spends himself in a worthy cause; who' if we wins' knows the triumph of high achievement; and who, if he fails, at least fails while daring greatly, so that his place shall never be with those cold and timid sould who know neither victory nor defeat."
-"The Man in the Arena"

 

Plato et al,

Consider the actual situation: you are standing in front of the stationary wormhole mouth, and looking through the wormhole (that is, through the moving mouth).

To you, it will seem that everything outside the moving mouth is moving, while you will actually think that the "moving" mouth is stationary. So at first glance it would seem that if you traversed the wormhole, by the time you were exiting from the moving mouth you should be moving with the same velocity. However, upon further consideration I do not see why that should be the case. Why should it not be that when you exit through the moving mouth, your kinetic energy is the same as when you started, and you emerge on the other side only to watch the wormhole mouth zoom away from you?

When a wormhole mouth moves, I should think it's more akin to a transverse wave traveling on a taut sheet of rubber. The individual rubber particles don't actually experience any "horizontal" motion. It's hard to describe, but imagine that the wormhole is visualized in 3D by taking two sheets of plastic, cutting a hole in each, and joining the edges of the holes so that the two sheets form a single surface, with a smooth "throat" connecting the two planes. Now, fix one end of the throat, and try to move the other one along its plane. Since plastic has to be conserved, you are going to have to shove plastic through the wormhole along its leading edge, and pull plastic out of the trailing edge -- to maintain the same geometry. This means that there will be spacetime "currents" evoked by the moving mouth at the stationary mouth (spacetime is going to be sucked into the stationary mouth from certain directions.) But regardless, the two motions of spacetime at the moving mouth (since they are opposite in direction) should cancel each other out near the mouth's middle, so that there is no overall spacetime movement at that point -- hence, no imparted velocity.

I don't know if any of this makes sense, but I really am having a hard time putting this in words without drawing pictures.

P.S.

In thinking about this typical wormhole analogy (with two flat sheets connected by a throat), I can't help but arrive at the conclusion that, if one of the wormhole mouths is moving while the other remains stationary, the actual distance (through the wormhole) of the two mouths cannot remain constant! That is, the trip through the wormhole will be either shortening, or lengthening -- though that should have nothing to do with time travel...

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I am; therefore I think.

[This message has been edited by Boris (edited May 27, 2000).]

 

“Time is but the stream I go fishing in. I drink at it, but while I drink I see the sandy bottom and detect how shallow it is. It's thin current slides away, but eternity remains.” - Henry David Thoreau

 

Indeed time travel is possible. This Clinton-era thread is proof.

 

In practice, time travel will never be possible, only perhaps in the weird quantum world of sub-atomic particles (and below).

 

Regardless of any theories already made, I think that time travel is not possible

 

You can never get to the past, because you didn't start your time machine before you started it.

 

Yep, it happened to me.
I landed earlier than I am departed.

 

they say it is easier to time travel to the future than it is to the past..

i say the proof of backwards time travel is in this thread..(7 posts ago it was 5-27-00)

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The O.P. asks if Time Travel is theoretically possible.

Define time:
Time, as described by Einstein in Relativity, is the measurement of change brought on by Motion. Within the Universe, motion and change are a constant (even if the rates of each are not); time is not a constant.
Since time is not a constant, it is not subject to alteration.
An analogy: Imagine you have a cup of coffee. That cup of the coffee is the Entire Universe.
You pick up the canister of powdered coffee creamer and sprinkle some onto the coffee. That powdered creamer represents 'matter' in the universe. It represents space and therefor: time.
The creamer sits on the top of the coffee, floating there motionlessly. You can see particulates, just sitting there. You pick up the coffee stirrer and start swirling it through the coffee. Motion has been added to the Universe. You can see the particulates dragging with currents and eddies, swirling around- Change is happening- time is measured as passing. Since time is not a constant, the amount of change measured is determinant only in pockets; you'll have different motion, and therefor rate of change, measured for different temperature and material consistencies in the coffee.
Differing motion against mass will result in different relatively perceived rates of change.

In order for Time travel to be possible, one would have to Undo Change. Literally. This "undoing of change" would have to be throughout the cosmos.

To travel backward in time, you must undo all motions and change within the entire universe- reverting it back to its exact state and position at the point of contact with the 'past.' Clearly, impossible for anything that exists within the Universe.
One must exit the Universe and build a machine that has enough energy and calculating power to alter all matter and states within the universe.

To accelerate change, you have only your own relative viewpoint to play with. You cannot accelerate change for all within the universe any more than travel back in time, but you CAN do it for yourself or anyone traveling with you by accelerating to near the speed of light. Since you cannot undo change, you cannot visit the future and return to the past. You're stuck there.

All of which renders the grandfather paradox moot.

As Prof. Farnsworth pointed out (With some help from the Harlem Globetrotters); The Doom Field has a self correcting paradox resolver.

 

Time is a concept of man that describes a rate, it is immaterial and therefore impossible to travel through. Of course, the only real way to "travel" time is to go to sleep and suddenly its morning when you wake up.