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Offline yor_on

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How does time relate to the photon?
« Reply #50 on: 03/10/2010 09:29:41 »
Sorry JP, missed your reply as I was 'filling in' my question. But yes, that's one answer. We can use those experiments we already made for testing the theory to prove that it still holds.
==

Ahhaa :) But that's where we don't agree JP. I don't find it meaningless to look at from a photons frame. The only way that would be meaningless would be if they didn't exist for us. But they do, and therefore I will guess :)

And no, I assume that the reason we exist is our arrow of time, aka a 'clock', and I also assume that the reason we can measure that light to have a velocity is that same 'clock' ticking for us. And then I assume that without a clock you can't discuss a distance, and I don't have to discuss it from the frame of a photon to reach that conclusion.

But applied to that frame you either have to define how the photon can 'propagate' or ..
Well, as I see it :)
=

Tachyons though :)
That's another parcel of fish.
« Last Edit: 03/10/2010 09:50:30 by yor_on »
 

Offline JP

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How does time relate to the photon?
« Reply #51 on: 03/10/2010 11:24:01 »
Ahhaa :) But that's where we don't agree JP. I don't find it meaningless to look at from a photons frame. The only way that would be meaningless would be if they didn't exist for us. But they do, and therefore I will guess :)

Meaningless might be a strong word, but how would we go about explaining what a photon experiences (if it is massless, that is)?  No theory covers this, so some new description would be required.  Something beyond special relativity, at least.
 

Offline lightarrow

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How does time relate to the photon?
« Reply #52 on: 03/10/2010 12:07:50 »
I don't find it meaningless to look at from a photons frame. The only way that would be meaningless would be if they didn't exist for us.
No, the only way in which such a frame could exist would be if photon's mass were not zero. Maybe you have not totally clear what a frame of reference is: not a simply abstract mathematical description, but a system of synchronized clocks put in all points of space (at steady intervals), or the possibility to really do it *physically*. You *can't* do this with massless particles.
 

Offline yor_on

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How does time relate to the photon?
« Reply #53 on: 03/10/2010 14:57:01 »
"I assume that the reason we exist is our arrow of time, aka a 'clock', and I also assume that the reason we can measure that light to have a velocity is that same 'clock' ticking for us. And then I assume that without a clock you can't discuss a distance, and I don't have to discuss it from the frame of a photon to reach that conclusion. "

Am I wrong there?


 

Offline yor_on

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How does time relate to the photon?
« Reply #54 on: 03/10/2010 23:06:24 »
Another point worth noticing.
If a photon was found to have a restmass it seems to me that it could be considered to intersect? According to this definition..

"One of the most basic geometrical ideas is intersection. In relativity, we expect that even if different observers disagree about many things, they agree about intersections of world-lines. Either the particles collided or they didn't. The arrow either hit the bull's-eye or it didn't. So although general relativity is far more permissive than Newtonian mechanics about changes of coordinates, there is a restriction that they should be smooth, one-to-one functions. If there was something like a Lorentz transformation  for v=c, it wouldn't be one-to-one, so it wouldn't be mathematically compatible with the structure of relativity. (An easy way to see that it can't be one-to-one is that the length contraction would reduce a finite distance to a point.)"

Am I right there?
 

Offline JP

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How does time relate to the photon?
« Reply #55 on: 04/10/2010 06:07:11 »
Let's come at this from a different direction.  When Einstein came up with special relativity, one of the postulates was that the speed of light is constant for all inertial observers.  The theory ended up describing how inertial observers who are moving relative to each other will measure space and time differently.  One aspect of the theory is that since light speed is constant, it can't be in an inertial frame, so its point of view can't be described by special relativity.  Arguments that photons are "timeless" and so on are flawed in that they're trying to make the theory work for something it just can't work for (when I first learned special relativity, no on told us it wouldn't work for light, so I also thought that way).  Talking about what a photon experiences in terms of special relativity is meaningless, so if you want to talk about what it experiences, you'd have to somehow come up with a new theory, but in order to do that you'd have to have some way of relating that experience to something you could actually measure.  Since all measurements are made from our point-of-view as objects with mass, I suspect that's impossible, and your quote about intersections seems to be saying its impossible as well...

I think the quote above about world lines intersecting is getting at the point that all observers should agree on whether an event happens or not, no matter how fast they're moving.  They might measure things differently, but the event itself should still happen.  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. 

If photons are shown to have rest masses, then their point of view is described by special relativity, just as our point of view is.
 

Offline yor_on

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How does time relate to the photon?
« Reply #56 on: 04/10/2010 15:20:32 »
Yep, I agree JP, but this whole excursion is just to ring in what proof we have for that a photon really have to be that 'massless' 'timeless' 'point' of no displacement in SpaceTime. So all ways we can think up to ring in why it have to be that way is good to me. And if there was some way proving it to be different I would be very interested. And, as you say "one of the postulates was that the speed of light is constant for all inertial observers."

So how about an accelerating observer?
Accelerating non-linearly?

Will that frame give another speed for light?
« Last Edit: 04/10/2010 15:22:19 by yor_on »
 

Offline yor_on

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How does time relate to the photon?
« Reply #57 on: 04/10/2010 21:43:29 »
GoodElf wrote an interesting answer to a similar question of mine on another place. It it he comments that "The speed of light actually appears to be the thing keeping stuff apart and making all that space and energy out there in our universe." which I found to be rather worth thinking over. What he was talking about here was the invariance of that speed as measured from all 'inertial frames'. So what would happen if a photon would be found to have a restmass, as seen from this definition? Could you use this as a 'proof' why we don't expect a restmass?
 

Offline JP

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How does time relate to the photon?
« Reply #58 on: 05/10/2010 01:39:58 »
Yep, I agree JP, but this whole excursion is just to ring in what proof we have for that a photon really have to be that 'massless' 'timeless' 'point' of no displacement in SpaceTime. So all ways we can think up to ring in why it have to be that way is good to me. And if there was some way proving it to be different I would be very interested. And, as you say "one of the postulates was that the speed of light is constant for all inertial observers."

So how about an accelerating observer?
Accelerating non-linearly?

Still constant. You'd see the light getting Doppler shifted, though.
 

Offline JP

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How does time relate to the photon?
« Reply #59 on: 05/10/2010 01:43:35 »
GoodElf wrote an interesting answer to a similar question of mine on another place. It it he comments that "The speed of light actually appears to be the thing keeping stuff apart and making all that space and energy out there in our universe." which I found to be rather worth thinking over. What he was talking about here was the invariance of that speed as measured from all 'inertial frames'. So what would happen if a photon would be found to have a restmass, as seen from this definition? Could you use this as a 'proof' why we don't expect a restmass?

I'm not sure I understand what he's getting at.  The speed of light has to do with the expansion of the universe, I guess, in the sense that its a cosmic speed limit and that somewhat determines how general and special relativity work, but I don't see how it directly does what he claims.  If light has a rest mass, then this speed limit still appears to exist (experiments involving things other than light seem to verify it).
 

Offline CPT ArkAngel

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How does time relate to the photon?
« Reply #60 on: 05/10/2010 05:46:33 »
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.
« Last Edit: 05/10/2010 20:53:05 by CPT ArkAngel »
 

Offline yor_on

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How does time relate to the photon?
« Reply #61 on: 05/10/2010 05:58:48 »
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 :)
==

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.)
« Last Edit: 05/10/2010 06:07:32 by yor_on »
 

Offline yor_on

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How does time relate to the photon?
« Reply #62 on: 05/10/2010 06:18:35 »
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.
 

Offline CPT ArkAngel

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How does time relate to the photon?
« Reply #63 on: 05/10/2010 06:56:54 »
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
 

Offline lightarrow

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How does time relate to the photon?
« Reply #64 on: 05/10/2010 13:04:32 »
Like i said in another post, special relativity is a matter of perception and not reality,
What does this phrase mean?
 

Offline yor_on

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How does time relate to the photon?
« Reply #65 on: 05/10/2010 14:12:14 »
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.
 

Offline CPT ArkAngel

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How does time relate to the photon?
« Reply #66 on: 05/10/2010 16:10:17 »
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...
 

Offline lightarrow

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How does time relate to the photon?
« Reply #67 on: 05/10/2010 16:32:11 »
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?
 

Offline Ron Hughes

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How does time relate to the photon?
« Reply #68 on: 05/10/2010 16:43:09 »
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?
« Last Edit: 05/10/2010 16:57:34 by Ron Hughes »
 

Offline CPT ArkAngel

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How does time relate to the photon?
« Reply #69 on: 05/10/2010 17:27:58 »
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.
 

Offline yor_on

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How does time relate to the photon?
« Reply #70 on: 05/10/2010 18:02:31 »
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?
==
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?
==

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?
« Last Edit: 05/10/2010 18:27:43 by yor_on »
 

Offline yor_on

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How does time relate to the photon?
« Reply #71 on: 05/10/2010 18:37:32 »
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*
« Last Edit: 05/10/2010 18:41:53 by yor_on »
 

Offline lightarrow

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How does time relate to the photon?
« Reply #72 on: 05/10/2010 19:09:52 »
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.
« Last Edit: 05/10/2010 19:55:12 by lightarrow »
 

Offline lightarrow

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How does time relate to the photon?
« Reply #73 on: 05/10/2010 19:51:01 »
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.

Quote
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).
 

Offline CPT ArkAngel

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How does time relate to the photon?
« Reply #74 on: 05/10/2010 20:33:28 »
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...
 

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How does time relate to the photon?
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