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Author | Topic: Expanding photons. | |||||||||||||||||||||||||||
Larni Member Posts: 4000 From: Liverpool Joined: |
I'm aware that space/time is expanding and that the red shift that far off galaxies exhibit is due to the expansion of space/time shifting the wave length of light towards the red.
What puzzles me is that if space/time is expanding, would that not include the photon and its motion too? Also, if the far off galaxies are moving away faster than the near ones, would not the photons and their motion 'shift back' as it approaches our telescopes? If these are dumb questions with obvious (well, obviously not to me ) answers I appologise in advance; I normally hang out in the 'Is it Science' campus and cosmolgy is a bit of a new frontier for me. Cosmolgy please.
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Admin Director Posts: 13032 From: EvC Forum Joined: Member Rating: 2.1 |
Thread moved here from the Proposed New Topics forum.
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crashfrog Member (Idle past 1493 days) Posts: 19762 From: Silver Spring, MD Joined: |
What puzzles me is that if space/time is expanding, would that not include the photon and its motion too? Is there even a model of relativistic cosmology that models photons?
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Phalanx Member (Idle past 5738 days) Posts: 31 From: Old Bridge, NJ, US Joined: |
forgive me if i'm being a bit obtuse...
but, I always thought that a photon was a photon, regardless.
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Ingvar Inactive Member |
The photon is a misinterpretation of measurings of heat radiation that demonstrated a constant fractional displacement difference between the wave-units.
You can see evidence on my homepage The Unified Theory of Physics I have also measured from a simple experiment that sound follows the same entropy law, but of course with the specific constant for that matter. These simple experiments explain how energy is decreasing towards equilibrium. Edited by Ingvar, : Better explained Edited by Ingvar, : No reason given. Edited by Ingvar, : No reason given. Edited by Ingvar, : No reason given.
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Larni Member Posts: 4000 From: Liverpool Joined: |
So can anyone help me?
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Son Goku Inactive Member |
What puzzles me is that if space/time is expanding, would that not include the photon and its motion too?
The photon is a point particle (at all energy scales we've ever probed at least) so there is nothing to expand.The expansion of the universe does effect its motion of course. Also, if the far off galaxies are moving away faster than the near ones, would not the photons and their motion 'shift back' as it approaches our telescopes?
Photons don't move like balls, so if you take the photon picture of light then terminology like that doesn't apply.However if you take the wave picture red shift is the "shift back" in their motion. Although I'm not sure if I'm understanding you correctly.
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Larni Member Posts: 4000 From: Liverpool Joined: |
Thanks for the 'point' nature of the photon mate.
I guess I meant: is far away space is receding quicker than near space? But I think its because of the 'amount' of intervening space that is expanding is huge. I think I have answered my own question here, lol.
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cavediver Member (Idle past 3669 days) Posts: 4129 From: UK Joined: |
Just a quick point - all of this occurs in 4d space-time. We think in 3d, which means whatever picture/explanation we put forward for the red-shift is actually some projection of the "true" 4d story, into some shadow "3d" picture. There are many different possible projections and thus many different pictures, which is why you can hear of many very different explanations - just as the question "how big is your shadow" has many different answers...
From the photon's own POV, there is no expanding space. It doesn't even move. The distance between the point of emission and point of absorption is zero
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Silent H Member (Idle past 5845 days) Posts: 7405 From: satellite of love Joined: |
From the photon's own POV, there is no expanding space. It doesn't even move. The distance between the point of emission and point of absorption is zero
I'm interested in this statement being fleshed out more. Are you meaning because time would not seem to pass and so there is no motion, or that its behavior is "wormhole" like? It seems intuitive to me that if space is expanding that would have to mean something for photon, some change in how it behaves. In fact that raises a question in my mind of if there are any possible (intriguing) consequences for speed of light being fixed in a universe that is expanding (or accelerating)? I know these are more dumb questions... but that's why I need to ask them. holmes "What a fool believes he sees, no wise man has the power to reason away." (D.Bros)
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sidelined Member (Idle past 5934 days) Posts: 3435 From: Edmonton Alberta Canada Joined: |
cavediver
From the photon's own POV, there is no expanding space. It doesn't even move. The distance between the point of emission and point of absorption is zero Is it also correct to say that time also does not move for a photon from its POV?
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JustinC Member (Idle past 4870 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
quote:I'll take a crack at this. You are right that time would not pass from a photons POV, but I think the more relevant reason is that from its point of view, it is the rest of the universe that is moving a the speed of light. In this case, all distances in the direction in which it would move are contracted to zero. Once it orients itself where it wants to go, there's no where to go! It violates no law to say that matter is moving at c because all relativity says is that no matter can be accelerated to c(or accelerated down to c is you were somehow traveling at plus c).
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cavediver Member (Idle past 3669 days) Posts: 4129 From: UK Joined: |
I'm rather busy so please forgive the short replies...
Are you meaning because time would not seem to pass and so there is no motion, or that its behavior is "wormhole" like? Aspects of both. Time and distance and are same thing from the 4d perspective (just like distance on a piece of graoh paper is not usually differentiated into x-distance and y-distance) Two points (events) in space-time that are connected by a light-ray (null-ray as we call it) have zero time/distance between them. All the events along the light-ray are collapsed into one point. This seems strange but we don't often think of single space-time pomits/events as being the end markers of a stretch of time or distance. We tend to think of Newtonian time between slices of Newtonian space, and Newtonain distances at one particular moment of Newtonian time. So not really wormhole-like behaviour, more like the "folding space" concept introduced in Lynch's verson of Dune.
if space is expanding that would have to mean something for photon, some change in how it behaves. It is more of a change in the way we perceive the photon.
if there are any possible (intriguing) consequences for speed of light being fixed in a universe that is expanding (or accelerating)? No, it doesn't change anything. But that is not to say that the subject is not intriguing! GR is bizarre and wonderful enough without trying to muddy the waters further
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Son Goku Inactive Member |
I made a stab at explaining this in detail before.
If you want to read: EvC Forum: Time, a brief history Basically messages 46 and 50-54 explain it.
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Silent H Member (Idle past 5845 days) Posts: 7405 From: satellite of love Joined: |
more like the "folding space" concept introduced in Lynch's verson of Dune.
I can't remember lynch's dune very well. For a geek reference how about "event horizon" with the analogy to folding a piece of paper so one point in space touches another and then space is folded back to the flat sheet (with the photon now at the other point)? holmes "What a fool believes he sees, no wise man has the power to reason away." (D.Bros)
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