[CPT ArkAngel]

You have to use synchronized time clocks and taking account of accelerations. Like i said in another post, special relativity is a matter of perception and not reality, if you want to know what will happen, you have to use acceleration in a general relativity point of view. A and B have to communicate to know what is really happening...

What Ethos wrote is interesting because a photon is simply a quantum of electromagnetic wave and electromagnetic wave seems to be the ultimate carrier of information for our brain perception... our perception of reality.

[yor_on]

Yep JP, didn't think that one through, painfully obvious that one.
We had no problems with beams before relativity came

But we have now
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CPT "special relativity is a matter of perception and not reality."
You don't trust the separate 'frames' reality then?

(And no JP, GE was speculating there. It was me getting stuck on the formulation I'm afraid.
It had such a nice ring to it.)

[yor_on]

JP you wrote "It would be nonsensical, for example, if you could make two asteroids miss each other or collide with each other simply by moving faster or slower as you viewed them.  The above quote seems to be claiming that there is no theory compatible with special relativity that would give photons this property as they "viewed" the universe." and I think I agree. To have it be like that would make our SpaceTime into fragments and the 'wholeness' we imagine a joke.

But there is still that example in which a attacking Andromeda space-fleet will attack before or after, depending on which one of two persons you are, and depending on the direction of their walks as they cross each others path. That is, to one it haven't happened at all, being in that ones future world-line, whilst in the other pedestrians world-line the space-fleet already have left Andromeda.. I can look it up if you're interested. Got to admit that it made no sense to me, even if true it becomes weird to think of.

[CPT ArkAngel]

yes you are right Yor on but you have to use accelerating frames of references and not only inertial frames. I wrongly associated acceleration with general relativity only...

http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Relativity/SR/acceleration.html

[lightarrow]

Like i said in another post, special relativity is a matter of perception and not reality,

What does this phrase mean?

[yor_on]

I think I see what you mean, I've always had problems separating those two theories, So I usually end up thinking of light instead, only separating it when I really need to understand what the he* I think I'm talking about

And that's also why I asked about lights invariance in a accelerated non-linear frame. Because I see it that way too, assuming that we're discussing 'black box scenarios'. There is just one thing more, assume a uniformly moving rocket, defined as being close to light as seen against Earth (inertial frame:). Will they too observe a Doppler shift? And it's a 'black box' scenario, not using any stars, or light, outside the ship. Forgot to mention that before.

[CPT ArkAngel]

Like i said in another post, special relativity is a matter of perception and not reality,

What does this phrase mean?

I should have said special relativity using only inertial frames of reference.

See the "Twins paradox". If you only use inertial frames for calculations, you don't make any distinction on who is moving relative to the other. In this way, if two people are moving relative to each other, they should both think that the other is aging at a slower rate. It is paradoxical... Which one has the truth? You need to take account of acceleration and synchronized clocks to really knows what is happening...

[lightarrow]

I should have said special relativity using only inertial frames of reference.

See the "Twins paradox". If you only use inertial frames for calculations, you don't make any distinction on who is moving relative to the other.

Let's imagine that I am in an inertial frame even if I don't know it, and my sibling goes to Proxima Centauri and come back, but we don't know this, we only know that we are in a relative motion and that our distance starts to zero, increases to a maximum then decreases to zero again. During our relative motion he sends me light pulses every second of his time and I send him light pulses every second of my time.

Do you think that I'm not able to make the correct computation according to SR and to conclude that I'm in an inertial frame and he is in an accelerating frame?

[Ron Hughes]

There in lies the crux of the problem. All you can know from his signal is that it is red shifted when he is moving away and blue when he returns, all he can know from your signal is it's red shifted moving away and blue coming back. How can either of know which is the one moving?

[CPT ArkAngel]

You should be correct because you use an accelerating frame of reference for the one who is accelerating (and or decelerating). You won't be correct if you use only inertial frames of reference for both of them.

The way i see it is, relative speed alone will produce measurement distortion of spacetime but acceleration produce true distortion of it... Correct me if i am wrong.

[yor_on]

Lightarrow, I have a clear problem with finding a clear definition of how an acceleration comes to be in time. How small can I make my 'frames of reference'? Planck sized? Like Planck time? And looked at this way, where do I define the 'acceleration'?

It falls back to how I see an accelerating motion for me, or for that sake, take a circle drawn on a paper. Is it a really a 'bent form' or can I also see it as an infinite amount of straight lines put together? slightly placed at an angle to each other? That one seems 'legal' to ask, but the opposite, describing a straight line in form of infinitesimally small pieces of circles? That one seems to become contradictory in terms to me? It may all be semantics, but to me it creates confusion, not that this is any surprise, neither to you, nor me I guess

And differing the light seems to build on the assumption of them both having an common origin, and so a common 'history' defining them to each other, before they interpret the information the red/blue shifted signals will give them?
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To see how I think make it a 'black box scenario' for them both..
How will they decide? Stupid of me
Of course you're correct..

You don't need a common origin for that one, you only need a 'history' and some way of defining that what you are receiving comes from the same 'origin'.

But still, how do I define what acceleration really is?
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Drawn to its utmost conclusion it suddenly seems that the only way I can define acceleration is by assuming 'times arrow' to be a 'flow'.  As treating 'times arrow' as 'instants' only brings me back to my first question?

[yor_on]

So, how about this?
There can only be straight lines, and what 'bends' are SpaceTime.
And Times arrow have to be a flow

*Running under my table*
==

Ah that should read *Most bravely running under my table*

[lightarrow]

There in lies the crux of the problem. All you can know from his signal is that it is red shifted when he is moving away and blue when he returns, all he can know from your signal is it's red shifted moving away and blue coming back. How can either of know which is the one moving?

The one who is accelerating is simply the one who sends less signals.
I mean, if we know for sure that one is in an inertial frame and the other is not, with that simple way we can established who.

[lightarrow]

You should be correct because you use an accelerating frame of reference for the one who is accelerating (and or decelerating). You won't be correct if you use only inertial frames of reference for both of them.

If both were in inertial frames at relative speed v ≠ 0, certainly we couldn't meet again to compare our time intervals, so it would be perfectly correct to say that the interval of time between two events is greater for me, in my frame, and that it's greater for him, in his frame.

Anyway, the twin paradox does not come from the fact that one is accelerating, in the sense that the *amount* of acceleration is not important; what counts is the fact that the situation is asymmetric, actually. You can see this asymmetry for example noting that in my frame I measure 4 light years as Earth-Proxima Centauri distance, while he measures less for lorentz contraction.

The way i see it is, relative speed alone will produce measurement distortion of spacetime but acceleration produce true distortion of it... Correct me if i am wrong.

Not even acceleration produces true distortion of spacetime. True distortion (that is, curvature) is only produced by energy/momentum (to be more precise, stress energy tensor).

[CPT ArkAngel]

There in lies the crux of the problem. All you can know from his signal is that it is red shifted when he is moving away and blue when he returns, all he can know from your signal is it's red shifted moving away and blue coming back. How can either of know which is the one moving?

The one who is accelerating is simply the one who sends less signals.
I mean, if we know for sure that one is in an inertial frame and the other is not, with that simple way we can established who.

The one who is accelerating can feel it or if you prefer, measure it...

[CPT ArkAngel]

You should be correct because you use an accelerating frame of reference for the one who is accelerating (and or decelerating). You won't be correct if you use only inertial frames of reference for both of them.

If both were in inertial frames at relative speed v ≠ 0, certainly we couldn't meet again to compare our time intervals, so it would be perfectly correct to say that the interval of time between two events is greater for me, in my frame, and that it's greater for him, in his frame.

Anyway, the twin paradox does not come from the fact that one is accelerating, in the sense that the *amount* of acceleration is not important; what counts is the fact that the situation is asymmetric, actually. You can see this asymmetry for example noting that in my frame I measure 4 light years as Earth-Proxima Centauri distance, while he measures less for lorentz contraction.

The way i see it is, relative speed alone will produce measurement distortion of spacetime but acceleration produce true distortion of it... Correct me if i am wrong.

Not even acceleration produces true distortion of spacetime. True distortion (that is, curvature) is only produced by energy/momentum (to be more precise, stress energy tensor).

What will happened to the energy momentum of an accelerating object? It will increase...

General relativity says that Gravity and acceleration are the same...

[Ron Hughes]

Light, no matter how you slice it movement is relative to the observer. The observer can never know whether he is moving or what he is observing is in motion.

[Ron Hughes]

BTW Ethos here is a pretty good demo of how time is related to a photon. It's located in new theories but JJ Thompson come up with it about hundred years ago. It was also in EM Purcell's text book on electricity and magnetism that was used for nearly ten years in the U.S.  http://www.thenakedscientists.com/forum/index.php?topic=34333.0;topicseen

[lightarrow]

What will happened to the energy momentum of an accelerating object? It will increase...

General relativity says that Gravity and acceleration are the same...

Not exactly, it's true only locally. But unfortunately I don't know much more of GR.

[Ron Hughes]

Do you mean that the inertial force I feel ten lights from Earth is different from what I would feel near Earth?