Can Light Travel Into the Future While We Explore Time Travel?

[PAllen]

I was thinking Doppler effect when someone told me that a clock ticks faster than your own as it approaches, normalises as it passes, and then runs slow as it moves away. Is this true even for inertial motion?

Yes, this is true of inertial motion, if you mean 'visually see' ticks faster/slower, etc. If you factor out doppler, the moving clock would be considered slow the whole time.

 

[PAllen]

Only if you don't put the common origin of the rocket twin's two frames at the turnaround event. You make him jump frames in a discontinuous way which creates the artificial shift in simultaneity. If you put the origins of the two frames at the same event as the turnaround, this shift in simultaneity won't occur.

Or if you just use one frame to analyze the entire scenario, there won't be any shifts in simultaneity no matter which frame you use.

I thought it was clear I was describing a non-inertial frame (coordinates) for the rocket in which the rocket is always the origin of said frame. I do not believe which point on such a time axis you declare to be t=0 has any impact on simultaneity. As for discontinuity, you can obviously replace it with an arbitrarily short continuous turnaround.

(The surface of simultaneity is function purely of a world line, and is conventionally taken to be the 3-surface 4-orthogonal to the world line at a given point).

My main point, I thought was clear, was to point out that if the rocket factored out doppler, they would always interpret stay at home twin going slow (except possibly during turnaround, and this portion can be made insignificant). If this is done, you can make various interpretations of the turnaround - including that the stay at home twin jumped far away in distance.

I don't find any of this latter approach very instructive - the only point was to highlight the difference between visual appearance of a clock and interpretation of such according to a theory - e.g. doppler.

 

[mrfrosty]

What I find hard to grasp is that if light has a speed, and if time is supposed to be frozen at this speed, then surely this would mean that time has a speed also. Which would beg the question of what would occur if something traveled faster than light. My understanding is that the only reason there is a limitation of light speed is due to the fact that an object has the appearance it does due to the light which is reflected from the object. If the object was moving faster than light, then it would not give light the opportunity to reflect from it, therefore the object would theoretically not appear. Sorry if this sounds a bit garbled but I find it difficult to explain the theory I am thinking of.

 

[phinds]

What I find hard to grasp is that if light has a speed, and if time is supposed to be frozen at this speed, then surely this would mean that time has a speed also. Which would beg the question of what would occur if something traveled faster than light. My understanding is that the only reason there is a limitation of light speed is due to the fact that an object has the appearance it does due to the light which is reflected from the object. If the object was moving faster than light, then it would not give light the opportunity to reflect from it, therefore the object would theoretically not appear. Sorry if this sounds a bit garbled but I find it difficult to explain the theory I am thinking of.

The fact that an object has to obey the universal speed limit has nothing to do with whether or not there are any photons bouncing off of it. In the absence of photons, it STILL takes infinite energy to get a body with mass up to the speed of light, thus it cannot be done 'cause we can't get infinite energy.

 

[Dale]

My understanding is that the only reason there is a limitation of light speed is due to the fact that an object has the appearance it does due to the light which is reflected from the object. If the object was moving faster than light, then it would not give light the opportunity to reflect from it, therefore the object would theoretically not appear.

By that same logic a supersonic aircraft should be silent.

The relativistic effects are not due to appearances or light's finite speed. They are what remains after an intelligent observer accounts for light's finite speed.

 

[mrfrosty]

That's understood about infinite energy. Now if you think about the theory of the idea, and the theory that you have enough energy to propel a mass at the speed of light, if you were to slowly accelerate up to the speed of light and have the ability to take measurements of time dilation in doing so, would both the acceleration and the amount of time dilation be proportionate with each other. For example, if the speed of light was used as a speed in the equation for time dilation, would the time be '0', ie at a stand still.

 

[mrfrosty]

A supersonic aircraft would be silent if you were in front of it, as the sound wave acts in a cone from the front of the direction of travel outwards to the rear, that is why you see a supersonic aircraft before you hear it. The sound wave is an effect from its movement.

 

[PAllen]

That's understood about infinite energy. Now if you think about the theory of the idea, and the theory that you have enough energy to propel a mass at the speed of light, if you were to slowly accelerate up to the speed of light and have the ability to take measurements of time dilation in doing so, would both the acceleration and the amount of time dilation be proportionate with each other. For example, if the speed of light was used as a speed in the equation for time dilation, would the time be '0', ie at a stand still.

No matter how much you accelerate, fast or slow, however long, the speed of light will remain the same for you, whether you emit the light or someone you are are zooming by at .9999999999999 c emits the light. The two signals will move at c past you, even if you have been accelerating at a billion gees for a billion years.

 

[Dale]

A supersonic aircraft would be silent if you were in front of it, as the sound wave acts in a cone from the front of the direction of travel outwards to the rear, that is why you see a supersonic aircraft before you hear it. The sound wave is an effect from its movement.

Similarly, your logic that a superluminal object would be invisible is not correct. In fact, there is a close analogy to sonic booms for EM radiation, called Cherenkov radiation. It is very visible. True, you wouldn't see it until the particle had passed, but you still see it quite clearly.

 

[phinds]

That's understood about infinite energy. Now if you think about the theory of the idea, and the theory that you have enough energy to propel a mass at the speed of light, if you were to slowly accelerate up to the speed of light and have the ability to take measurements of time dilation in doing so, would both the acceleration and the amount of time dilation be proportionate with each other. For example, if the speed of light was used as a speed in the equation for time dilation, would the time be '0', ie at a stand still.

Since you do not experience time dilation inside your superfast ship, it would not be possible to design an experiment to measure it. Time dilation is something seem by OTHER observers, not you.

 

[mrfrosty]

Lets see if I have got this right then.
1. Speed is related to time dilation, the faster the speed, the greater the time dilation.
2. Nothing can travel faster than the speed of light.
3. The speed of light is the point at which time is stationary.
4. If you could travel fast enough, you would not know that time has stopped or been dilated as it is only observed by somebody outside of your ship.

 

[phinds]

Lets see if I have got this right then.
1. Speed is related to time dilation, the faster the speed, the greater the time dilation.
2. Nothing can travel faster than the speed of light.
3. The speed of light is the point at which time is stationary.
4. If you could travel fast enough, you would not know that time has stopped or been dilated as it is only observed by somebody outside of your ship.

1) I would word #1 the other way 'round since what you have makes it sound like speed is created by time dilation.

2) correct

3) stationary relative to WHAT? Speed/time dilation is only meaningful in relationship to something. Actually, you don't get to "stationary" since that would imply traveling at c, which you can't do.

4) correct, although you don't get to a point of "stopped" since that would imply you are traveling at c, which cannot be done by anything with rest mass.

 

[nitsuj]

Lets see if I have got this right then.
1. Speed is related to time dilation,

Strickley speaking I'm not to sure.

I'd agree speed cooralates to time dilation. But I don't agree that speed is related to time dilation.

I'd raise gravitational time dilation where speed isn't required.

But I don't know enough about the details to say for sure.

 

[kamenjar]

...why doesn't light itself travel into the future? ...

It actually does. The photon's time in a way stops. From photon's point of view the universe ages in an instant as it goes from one end to the other end of the universe (not that there are ends - using this as a form of expression).

 

[Drakkith]

It actually does. The photon's time in a way stops. From photon's point of view the universe ages in an instant as it goes from one end to the other end of the universe (not that there are ends - using this as a form of expression).

I'm not sure a reference frame can be given for light.

 

[kamenjar]

I'm not sure a reference frame can be given for light.

I don't think either

..time in a way stops.

 

[Drakkith]

I don't think either

What?

 

[mrfrosty]

My problem with the theory of photons is that light has a speed and although it is very fast, it is still measurable. I am convinced that the only limitation to speed is the fact that photons, the particles that allows us to see things due to them bouncing off of the object, are the limitations to speed as if the object was traveling faster than photons, theoretically, the object would be invisible, but it would still be there.

 

[phinds]

My problem with the theory of photons is that light has a speed and although it is very fast, it is still measurable. I am convinced that the only limitation to speed is the fact that photons, the particles that allows us to see things due to them bouncing off of the object, are the limitations to speed as if the object was traveling faster than photons, theoretically, the object would be invisible, but it would still be there.

The universe really doesn't care what you are convinced of. The universal speed limit is NOT based on photons and your belief is not supported by reality as it is currently understood by both experimental AND theoretical physics.

 

[Dale]

My problem with the theory of photons is that light has a speed and although it is very fast, it is still measurable. I am convinced that the only limitation to speed is the fact that photons, the particles that allows us to see things due to them bouncing off of the object, are the limitations to speed as if the object was traveling faster than photons, theoretically, the object would be invisible, but it would still be there.

We already addressed this. By this logic a supersonic jet or bullet would be silent. We know that they are not silent. Therefore your logic is wrong. When your logic is shown to contradict fact then you must discard your falsified hypothesis and come up with a new theory that correctly fits the facts.

 

[HallsofIvy]

Vision is not the only way we "observe" the world! Even blind people can be physicists.