Paradox within the twin paradox

cavalier3024

ok, so first, you cant define an absolute speed since there is no such thing as 'speed relative to C'. that is because no matter how fast you are moving, you will always see the light moving at the same speed, C.

about the paradox - its really simple. So you say that there are two clocks, A and B, that are moving toward each other.
form A's point of view A is stationary and B is moving towards him at a certain speed.
from B's point of view B is stationary and A is moving towards him at the same speed.
so far we have a symmetry, and it is true that each will see the other ticks slower. but the symmetry is broken when you say that the clocks start at the same time, because the term 'same time' is reference frame related. if you mean that A 'sees' them starting at the same time (i.e that in A's reference frame they start simultaneously). then B will not see it that way! B will 'see' his clock starting much later then A's clock!
so:
*from A's view, the clocks started at the same time, and B's clock ticks slower. when they meet B have less ticks.
*from B's view, A started before B. so even though and A's clock ticks slower, B will still show less ticks when they will meet. just like A is seeing it. no paradox.

ghwellsjr

You are absolutely correct in everything you said in this paragraph, except that I would not have made the restriction "due to the laws of special relativity", I would have said "due to the facts of nature".

Now here is what you need to understand about special relativity. Since we cannot know which is the absolute stationary frame, we can arbitrarily pick any inertial reference frame and assume that it is the one and only absolute stationary frame that only Mother Nature knows about and everything will be consistent and behave according to all the laws of nature and we will have no way of knowing if we picked the "wrong" absolute stationary frame. Mother Nature won't tell us if we are wrong and she appears not to care.

But note, you have to assume that this is the one and only reference frame. You cannot talk about any other reference frame. You have to specify everything in terms of this one frame that you selected.

Now, if you want, you can decide that you don't like that reference frame anymore and you want to pick another arbitrary one that is defined relative to your first one. Then you use the Lorentz Transform to rebuild eveything from your first frame so that it is now defined correctly in your second frame and you treat it as the one and only absolute stationary frame that only Mother Nature knows about and again, everything will be consistent, etc, etc, etc.

Don't make the mistake of thinking that multiple reference frames co-existent at the same time, such as the people on earth are in a stationary frame and the people on the rocket ship are in a moving frame. If you do that, you will have to transform everything from one of those frames into the other frame before you can meaningfully discuss what is happening.

teachmemore

There is a big difference between light being at rest and light being trapped in a frame of reference. One is not possible and one is. What I claimed is completely possible under the laws of physics.

teachmemore

As you describe B 'sees' them as starting at the same time. Everything is done from B's reference frame.

I altered it slighly though to make the end points effectively at the same point in space. ie. the reference frames are touching so that they exchange data instantly.

This was done through a hypothetical device which exists in the same reference frame as clock/counter B, but at the same position as the clock/counter A when it passes the device. Counter B knows the distance of this device relative to itself and can therefore calculate the elapsed time since B was 'switched' by A.

Do you see? Normally, B would receive the first pulse from A, telling B that A had started at a point in time when from A's reference frame, it had already started ticking. BUT, through this device, B's frame of reference is physically in contact with A at the moment it starts ticking, so that through B's frame of reference, information is sent to B about the earlier time in which A started, all through direct physical contact.

The difference between your thought experiment here and mine, is that both reference frames are touching one another at both end points, when the clock A starts, and when the clocks meet and touch one another in space. This allows information to be sent to clock B, that it would otherwise not have access to.

Edit: So I guess the question is - how does instant traversal of data between reference frames at the two end points affect the problem?

ghwellsjr

I also cannot understand what you mean by the two pulses of light "no longer moving apart". Are you thinking that the medium slows them down until they get trapped and eventually stop?

Please explain.

teachmemore

It is not that important, since this definition is incomplete, but ya, what I meant was that two two pulses of light are trapped within the same frame of reference. As to how the light is trapped there, it is unimportant. It could be by particle absorption, or by being reflected between theoretically perfect mirrors - doesn't matter.

teachmemore

Eventually stop? Sorry? No that is impossible. I just meant that they become trapped at a fixed distance apart from one another, which would imply that they are in the same frame of reference.

ghwellsjr

Well it does matter if you have some incorrect or incomplete concepts of matter, time, space and light, and their relationship to a frame of reference.

I'm wondering why you would think in any sense that "two pulses of light are trapped within the same frame of reference" and not think that about everything else, all matter is equally trapped within the same frame of reference. But then, the same two pulses of light are also trapped in any other frame of reference along with all matter. I just don't know why you are thinking about things being trapped. You need to explain.

ghwellsjr

You think that two pulses of light traveling in opposite directions "become trapped at a fixed distance apart from one another"? Why do you think this?

teachmemore

Firstly, the definition was using the scenario of two pulses of light becoming trapped at a fixed distance apart; no statement was being made about what would happen if two arbitrary light pulses were sent in opposite directions.

Secondly, the definition is incomplete, because the scenario is insufficient to define an absolutely stationary reference frame, so there is no need to dwell on it.

Do you not believe that it is possible for two beam of light to become fixed at a distance between one another? If so, please explain why it is not theoretically possible.

matheinste

My physics is a bit rusty but I thought that light in a medium still travelled at c and that absorption and re-emission processes caused the overall delay. What you mean by trapped in a medium, or at a certain distance apart in a medium I cannot even guess. However, I am no expert on such matters, but I do have a query: if light is at rest or trapped in a medium, how would we see it.

Matheinste.

teachmemore

I don't know why you are having such a hard time with the word trapped. It just means confined to a fixed coordinate or set of coordinates within the frame of reference.

All matter IS at a fixed coordinate within a frame of reference. It does not need to be "trapped" to remain there because it is part of the frame of reference. Light on the other hand always travels at c relative to any frame of reference; hence, it must be trapped to remain at a fixed coordinate within the frame of reference. In a sense, absorption of light into matter accomplishes this feat. Or, creation of matter from light, as has been done in high speed particle accelerators.

teachmemore

We would not be able to see the trapped light pulse.

An example of a trapped light pulse is the "light clock" regularly used in special relativity thought experiments.

Edit: Another example would be an absorption process where the light is permanently absorbed as part of the particle; and is not re-emitted. Usually, photons will be re-emitted, but we have no way to tell that those photons are the same photons that were absorbed - I mean, at least not by standards of modern physics - maybe one day someone will come up with a theory that will allow us to find out such detailed information about the process of photon absorption and emission.

teachmemore

Does anyone have any thoughts on the issue of information being exchanged between reference frames that are in contact in space? ei. like my example of a device which is switched by a passing rocket?

ghwellsjr

You started off by saying two pulses of light were traveling in opposite directions. I guess from other posts you are simply saying that while they are light, they are traveling and have no fixed coordinates but when they hit something, then they have a fixed distance between them. Is this correct?

Now you are asking about two beams of light "to become" a fixed distance between one another and the confusion starts all over again. To me (and I think everyone else) a pulse of light is what you get when you turn a laser (or some other light source) on and off and a beam of light is what you get when you turn a laser (or some other light source) on and leave it on. The only way in which your question would make sense to me is if you were thinking of two lasers a fixed distance apart but otherwise aimed in the same direction and you turn them both on. Then the two beams would be parallel a fixed distance apart. But, somehow, I don't think this is what you had in mind because you used the expression "to become" and I suspect you are still thinking in terms of the beams being pointed in opposite directions. It is really important when discussing SR that we have a clear understanding of what light does so please explain what your concepts are.

matheinste

Hardly light at rest though.

As regards absorption, if a photon is absorbed I think it does not remain a photon, but its energy is absorbed raising the energy level or levels of bits within the atom by which it is absorbed.

But most of this is irrelevant to a definition pseudo absolute motion.

Matheinste.

teachmemore

Ya sorry. I meant pulse, not beam.