time travel

[truedeity]

i remember thinking this when i was a kid. so i wanted to ask this question because i think it's still a theoretically stable question that someone with some background in theoretical physics should address. based on our current understanding we cannot travel beyond the speed of light because Einstine said its not possible, as we approach the speed of light our mass would increase and the energy required would also be greater, the only way it could be done is if we had an infinite energy which cant happen. (though, it is said that black holes have an intense enough gravity to pull objects in near the speed of light.) we already established this understanding...

 

my question is more of a theoretical question that i'm just now remembering from my childhood. (yeah i knew all this before i was 10) it's sort of a 'what if' that i think still applies.

 

one thing that bothered me is supposing that we can travel faster than the speed of light. what would happen if you tied an infinitely long rope to a jet that travels beyond the light barrier? would part of that rope be in the future and the other part of that rope be in the past? if you follow the rope from beginning to end you should be able to find the jet right? so, let me rephrase lets say the rope is made out of some speical material that can sustain the travel, and it has plenty of length for the jet to take off and get to the speed of light and pass the speed of light. one end of the rope is tied to the statue of liberty in new york city, the other end of the rope is tied to the jet that travels beyond light speed. would the rope still be tied to both the jet and the statue? or would that rope hold open some sort of einstine-rosen bridge between past and future?

[Spyman]

First: IF you allow something to violate the known laws of science then you can no longer use those broken laws to predict what would happen.

 

Secondly: There are a lot of objects in the Universe receding from us right now with speeds greater than light due to the expansion of the Universe. If you would have a long enough rope and tied it to a spaceship that takes of in any direction then at some very very distant point it will seem to start to gain speed and accelerate to speeds greater than light, since it would gain recessional velocity from the expansion, as seen from the other end of the rope down on Earth.

 

Even if the rope should be on a suffiently large reel letting out rope freely it would not be able to spin with the speed of light and therefore the rope should start to streach faster than light and snap somewhere in between the spaceship and Earth. Further more if the rope should be able to streach out and hold for a short duration while the spaceship is receding slightly above lightspeed there would not happen any strange stuff along its extension and you would still not be able to climb it faster than light to reach the ship.

 

EDIT: I didn't realise that this thread was named "time travel" so I want to add that the hypothetical distant spaceship or any distant galaxy that we can observe today receding from us with speeds greater than light are not thought to be going backwards in time.

Edited March 31, 2012 by Spyman

[RichIsnang]

Technically as you walk down the road, you are travelling back in time a small amount, wether we can abuse this fact is I feel unlikely, but still possible, I feel that this is a law that will not be easily messed with, but then you could say the same thing about the laws of electromagnetism and I'm sure they did back when they weren't fully understood I imagine we will not be able to abuse these laws for a good while yet tho as it will take very advanced spaceships to do so

[IM Egdall]

Technically as you walk down the road, you are travelling back in time a small amount, wether we can abuse this fact is I feel unlikely, but still possible, I feel that this is a law that will not be easily messed with, but then you could say the same thing about the laws of electromagnetism and I'm sure they did back when they weren't fully understood I imagine we will not be able to abuse these laws for a good while yet tho as it will take very advanced spaceships to do so

 

 

Do you mean by moving down the road, your time is running slower than time for a clock on the road? In other words, time dilation?

[RichIsnang]

Of course

[IM Egdall]

Of course

 

OK. Thanks for the clarification.

 

So if you walk down the road and return, your wristwatch will show that less time went by for you than the clock at rest on the road (assuming extremely accurate clocks). So more time has gone by on that spot on the road than time for you. So you return to that spot on the road a tiny bit into the future. (I think I got this right).

 

This kind of time travel is just what happens any time we leave a place and return to it. It's just that the effect is so small we don't notice it.

[Superfusion]

OK. Thanks for the clarification.

 

So if you walk down the road and return, your wristwatch will show that less time went by for you than the clock at rest on the road (assuming extremely accurate clocks). So more time has gone by on that spot on the road than time for you. So you return to that spot on the road a tiny bit into the future. (I think I got this right).

 

This kind of time travel is just what happens any time we leave a place and return to it. It's just that the effect is so small we don't notice it.

 

I see, I knew that if you left earth for long periods of time and continued to move away from it when you returned you will have traveled into the future and made a massive jump if it was a long time and high speed. But i did not know that this was true on all scales in all cases. That is interesting.. This could lead to a conversation about space-time and some kind of multij existence. Perhaps you are living in all times. In that case in a complicated way your fate is already decided but you have already decided it. Just a brush over how it might work, Its likely something that would take a long time if never to understand and dig into and has alot of complicated things involved with it.

[questionposter]

First: IF you allow something to violate the known laws of science then you can no longer use those broken laws to predict what would happen.

 

Maybe you can't go back in time by traveling faster than light, but there's plenty of physics that have implications if you move backwards in time, and theoretically you should be able to, like if I just move backwards on a function where time is the x axis, that's going backwards in time.

[Spyman]

Maybe you can't go back in time by traveling faster than light, but there's plenty of physics that have implications if you move backwards in time, and theoretically you should be able to, like if I just move backwards on a function where time is the x axis, that's going backwards in time.

AFAIK there is no theoretical evidence that we should be able to travel backwards in time.

[khaled]

A frame with a very low time flow rate, we'd see the world progress faster on the outside .. that'd be traveling through time forwardly

 

I agree with Spyman, that traveling backwardly in time doesn't even have a theoretical evidence

[questionposter]

AFAIK there is no theoretical evidence that we should be able to travel backwards in time.

 

What about quantum weirdness and time symmetry? I'm not saying there's observable evidence or anything at this point, but there's reasons why the whole time travel theory caught on.

Edited April 4, 2012 by questionposter

[IM Egdall]

AFAIK there is no theoretical evidence that we should be able to travel backwards in time.

 

 

I donno. I thought the equations of general relativity do not rule out time travel. And quantum mechanics says particles can travel backwards in time.

[Spyman]

What about quantum weirdness and time symmetry? I'm not saying there's observable evidence or anything at this point, but there's reasons why the whole time travel theory caught on.

I don't know that we have a positive scientific theory of time travel, all that we seem to have is a lack of conclusive evidence against it.

 

Time travel is the concept of moving between different points in time in a manner analogous to moving between different points in space. Time travel could hypothetically involve moving backward in time to a moment earlier than the starting point, or forward to the future of that point without the need for the traveler to experience the intervening period (at least not at the normal rate). Any technological device – whether fictional or hypothetical – that would be used to achieve time travel is commonly known as a time machine.

 

Although time travel has been a common plot device in science fiction since the late 19th century, and the theories of special and general relativity suggest methods for forms of one-way travel into the future via time dilation, it is currently unknown whether the laws of physics would allow time travel into the past. Such backward time travel would have the potential to introduce paradoxes related to causality, and a variety of hypotheses have been proposed to resolve them, as discussed in the sections Paradoxes and Rules of time travel below.

http://en.wikipedia.org/wiki/Time_travel

 

However, the theory of general relativity does suggest a scientific basis for the possibility of backwards time travel in certain unusual scenarios, although arguments from semiclassical gravity suggest that when quantum effects are incorporated into general relativity, these loopholes may be closed. These semiclassical arguments led Hawking to formulate the chronology protection conjecture, suggesting that the fundamental laws of nature prevent time travel, but physicists cannot come to a definite judgment on the issue without a theory of quantum gravity to join quantum mechanics and general relativity into a completely unified theory.

http://en.wikipedia.org/wiki/Time_travel

 

 

I donno. I thought the equations of general relativity do not rule out time travel. And quantum mechanics says particles can travel backwards in time.

I only have little knowledge of relativity and know almost nothing about quantum mechanics, but from my understanding although they not specifically rule out the possibility of time travel, neither of them makes any claims of an assured possibility thereof either.

 

The general theory of relativity extends the special theory to cover gravity, illustrating it in terms of curvature in spacetime caused by mass-energy and the flow of momentum. General relativity describes the universe under a system of field equations, and there exist solutions to these equations that permit what are called "closed time-like curves," and hence time travel into the past. The first of these was proposed by Kurt Gödel, a solution known as the Gödel metric, but his (and many others') example requires the universe to have physical characteristics that it does not appear to have. Whether general relativity forbids closed time-like curves for all realistic conditions is unknown.

http://en.wikipedia.org/wiki/Time_travel

 

Certain experiments carried out give the impression of reversed causality but are interpreted in a different way by the scientific community. For example, in the delayed choice quantum eraser experiment performed by Marlan Scully, pairs of entangled photons are divided into "signal photons" and "idler photons", with the signal photons emerging from one of two locations and their position later measured as in the double slit experiment, and depending on how the idler photon is measured, the experimenter can either learn which of the two locations the signal photon emerged from or "erase" that information. Even though the signal photons can be measured before the choice has been made about the idler photons, the choice seems to retroactively determine whether or not an interference pattern is observed when one correlates measurements of idler photons to the corresponding signal photons. However, since interference can only be observed after the idler photons are measured and they are correlated with the signal photons, there is no way for experimenters to tell what choice will be made in advance just by looking at the signal photons, and under most interpretations of quantum mechanics the results can be explained in a way that does not violate causality.

http://en.wikipedia.org/wiki/Time_travel

[IM Egdall]

Spayman: If by "assured possibility", you mean guarantee of time travel in physics, I agree. But as I said, physics hasn't ruled it out completely.

 

For example, see interesting time travel possibility using general relativity and quantum mechanics: http://physics.aps.org/story/v23/st18

 

But like the article says, we won't really know until we have a theory of quantum gravity.

[Spyman]

Yes, we agree, timetravel is not ruled out. What I have been trying to say is that it is not ruled in either, it is still an open question.

[IM Egdall]

Yes, we agree, timetravel is not ruled out. What I have been trying to say is that it is not ruled in either, it is still an open question.

 

Well put.

[emilievak]

Has someone counted the number of topic about time travel ? I think that is one of the most popular subject on this forum. A special section should be created for it !