Photon frequency loss over time?

[ratfink]

Nah,
energy is conserved.
if a photon has enough energy to expose a photographic plate on galaxy x, then surely it cannot expose it on galaxy y? It must have lost energy on the way.
Are you saying that whilst a photon exposes a photo of their hols on their plates it also exposes a photo on our photographicplates even though it 'lost energy' on the way? No way!

 

[ratfink]

Do I mean what one?

Ratfink can just refer to the responses I already gave in reference to the latter question.

The only previous response that I can find remotely relevant is

it's always wise to consider the possibility that you might yourself be misunderstanding something about them.

 

[SpaceTiger]

The only previous response that I can find remotely relevant...

This post is what I was referring to:

https://www.physicsforums.com/showpost.php?p=1002766&postcount=10"

Evidence for an expanding universe is also evidence for a curved spacetime.

 

[SpaceTiger]

Nah,
energy is conserved.

No, Garth is correct, energy is not always conserved in GR. If you've done research you believe contradicts this, please don't post it here, submit it to the Independent Research forum.

 

[ratfink]

No, Garth is correct, energy is not always conserved in GR. If you've done research you believe contradicts this, please don't post it here, submit it to the Independent Research forum.

This is incorrect. Energy conservation in GR is in dispute. Some say that energy is not conserved others say it is due to 'curvature'. I hope that this is not a 'warning' because you wish to avoid answering valid questions.

 

[ratfink]

So, would the photographic plate be exposed on both galaxies or only one?
This is what energy conservation is about (and forums for that matter too!)

 

[SpaceTiger]

This is incorrect. Energy conservation in GR is in dispute. Some say that energy is not conserved others say it is due to 'curvature'. I hope that this is not a 'warning' because you wish to avoid answering valid questions.

The only dispute is in appropriate definitions of energy in GR. See here:

http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html"

Unless I'm to interpret your previous post as advocating a particular pseudotensor definition of energy, then it belongs in IR.

 

[ratfink]

This is not peer reviewed and who are they?

 

[ratfink]

OK,
Let me spell this out.
B/W paper is not sensitive to red light. That is why we have red safelights in photographic darkrooms.
Light from a distant galaxy is redshifted.
I say that there must be a point where the paper is not exposed anymore.
You and Garth say "Oh the pricinciple of conservation of energy does not apply".
I say B**-t either the paper is exposed or it is not. It is all to do with the photoelectric effect.
Nothing to do with reference frame - we all see the same result.
So I will ask again. If the photon has enough energy to excite and expose a photographic plate on galaxy X, will it once it has been redshifted, be able to expose it on galaxy y?

 

[Garth]

No need to be rude.

Energy is not generally conserved in GR because of the time dilation caused by space-time curvature. The energy of a system can only be consistently defined at null infinity where curvature effects and gravitational waves become insignificant.

The reason this is so is energy is a frame dependent concept, moving frames, or frames at different gravitational potential, measure energy differently from one another. We do not all see the same result - that is the whole point of relativity, certain measurements are relative.

In GR it is energy-momentum, or particle rest mass, that is conserved.

Your photographic plate question is irrelevant. The exposed plates X & Y both record the photon, but at a later cosmological time, after more cosmic expansion, the plate Y records a redder image. That is what Hubble red shift is all about.

Garth

 

[SpaceTiger]

That's enough, the OP's questions have long since been answered. I'm locking this.