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Douglas Sykora

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How do photons lose energy?
« on: 06/02/2009 02:30:02 »
Douglas Sykora asked the Naked Scientists:
   
Consider a single photon that was emitted 13.3 billion years ago from the last scattering surface.  

It is a visible light photon.  As it travels across the universe, it arrives at earth today as a much lower energy photon because of the expansion of the universe the photon's wavelength has increased by about a factor of 1000.  

The single photon is still a single photon.  It has not divided into multiple photons, but it is much lower in energy (by a factor of about 1000) due to the fact that it has a much longer wavelength.  

Where did the energy go?

Does conservation of energy apply to this photon?  If not, why not?

Does it have something to do with the reference frame we are in here on Earth?

What is the relationship of our reference frame to the reference frame 13.3 billion years ago when this photon was emitted?  I have been struggling with this for well over a year and I have not found a good answer.  Please help.

What do you think?


 

Offline Vern

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How do photons lose energy?
« Reply #1 on: 06/02/2009 03:05:23 »
The conservation of energy does apply. The photon could have lost energy any number of ways; one; the speed of recession of the galaxy from which it came may have Doppler shifted it; or two; it may have encountered charged particles in its journey and gave up energy to them. It is a speculative notion, but any time a photon's path is bent and it encounters a charged particle, it must give up energy to that charged particle. This must cause it to shift further toward the red.

Don't take the speculative notion to school; it is purely speculative; it is my own pet hypothesis.
« Last Edit: 06/02/2009 03:07:22 by Vern »
 

Offline yor_on

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How do photons lose energy?
« Reply #2 on: 06/02/2009 07:24:23 »
First of all Douglas. If your photon had a specific lightquanta I would expect it to have it still.
The expansion is about space, not particles.
Your photon is called 'timelsess' for a reason.
It doesn't care about 'our' count of the years, the only time 'passed' for that photon will be at its impact.

That's one of the strangest things with this Universe, that time doesn't 'count the same' for different objects.

Even thought you can notice a beam of light, you are not really noticing the photons traveling.
You are noticing their interaction with 'matter/atoms' as they gets absorbed into electron shells and 're emitted' as 'new' photons.
If I'm correct that should mean that in the absence of matter you will never be able to observe any light at all.
There are some ideas trying to treat a photon when meeting the electron shell as being 'reflected' in some mysterious way, I don't think so though.
But that doesn't really matter for your question.

Your light never tires, although we might:)
And 'conservation of energy' is for the universe as a whole.
It's not needed for explaining 'timeless' photons.

And this I would call a 'main stream' image:)
« Last Edit: 06/02/2009 07:29:06 by yor_on »
 

Offline LeeE

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How do photons lose energy?
« Reply #3 on: 06/02/2009 12:58:01 »
That's a very good and well thought out question Douglas.

As you mentioned 13.3 billion years ago and the last scattering surface you're talking about the CMBR here.  You also ask if it may be something to do with the reference frame  we are in, here on Earth, and this is the answer.  In short, the effect of the expansion of the universe has been to introduce a relative velocity between the frames, as they are now further apart than they used to be, and if you take this into consideration everything adds up again.  If you were to re-align one of the frames (in practice, the observers frame is the only one that can be changed) by removing the difference between them i.e. reducing their relative velocities to zero,  you'd then see the energy that seemed to have been lost.
 

Offline Vern

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How do photons lose energy?
« Reply #4 on: 06/02/2009 13:29:37 »
I agree LeeE; a Doppler shifted photon has not lost energy; I was thinking of things that might actually reduce the energy of a photon.
 

lyner

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How do photons lose energy?
« Reply #5 on: 06/02/2009 15:31:25 »
I agree LeeE; a Doppler shifted photon has not lost energy; I was thinking of things that might actually reduce the energy of a photon.
It has lost energy in as far as it can't transfer as much energy to what it hits as when it left home.
 

Offline Vern

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How do photons lose energy?
« Reply #6 on: 06/02/2009 17:10:39 »
Ok; I see now that you're right. I was typing without thinking :)
 

Offline LeeE

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How do photons lose energy?
« Reply #7 on: 06/02/2009 20:16:35 »
I agree LeeE; a Doppler shifted photon has not lost energy; I was thinking of things that might actually reduce the energy of a photon.
It has lost energy in as far as it can't transfer as much energy to what it hits as when it left home.

... which is because what it hits will be in a different referential frame to the one that it started it's journey from.
 

Offline Vern

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How do photons lose energy?
« Reply #8 on: 07/02/2009 00:54:26 »
Note to self: Self; count slowly to ten before starting to respond to a post :)
 

Offline chris

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How do photons lose energy?
« Reply #9 on: 07/02/2009 23:09:13 »
I don't understand this answer relating to referential frames. The photon has less energy now than it one did, if I measure it. So where is that missing energy?

Chris
 

Offline yor_on

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How do photons lose energy?
« Reply #10 on: 08/02/2009 00:02:20 »
Frames is definitely confusing :)

But 'red shift', if photons is of a specific, not changing, light quanta, must be a 'relative' effect.
If we have two objects moving away from each other (frame_A frame_B), and light is 'time less' internally.
 
Then red shift, which consists of a longer wavelength, or if one like, fewer photons per distance counted, or time slice, will be a relation.
That 'relation' is then expressed as red shift.
The faster that frame_A moves away from the light chasing it, the more red shifted that light will appear from frame_A.

When it 'catch up' to frame_A there will be fewer photons per time slice hitting that object.
But the photons will still be of the same energy content.
As photons are 'time less' internally they have no reason to 'loose' any energy as time isn't there internally.

I'm not sure how to describe it in a wave way though.
Phase velocity?
And what should I see as the group velocity here?

Another strange thing about it is that if we turn the table around and have two frames (A and B) moving towards each other.
And then measure the light coming towards you at frame_A from frame_B, then that light still will be moving at 'only C' in space.
The only thing we will notice is a so called 'blue shift'.

So it doesn't matter if we move towards or moving from that light.
It will not change 'speed' when observed, the only effect we will notice is a red / blue shift relative us observing.

(So yes Lightarrow, I definitely see your point made before:)

But I would really like to see someone describe it as waves, with as little math as possible.
As I don't know how to describe this that way.
« Last Edit: 08/02/2009 00:06:41 by yor_on »
 

Offline Vern

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How do photons lose energy?
« Reply #11 on: 08/02/2009 00:21:00 »
There is no problem describing the red shift as waves. The wave length is longer. The distance from trough to trough is greater. If the causing factor is a Doppler shift, the greater distance from trough to trough is because the generator of the wave is moving away.

There is speculation that a photon of light moving through space for billions of years might lose energy by some other process. One such might be Halton Arp's Tired Light scheme.
« Last Edit: 08/02/2009 01:20:14 by Vern »
 

Offline yor_on

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How do photons lose energy?
« Reply #12 on: 08/02/2009 00:48:24 »
Vern, if you look at it as a wave instead of particles then where are the (light quanta's) 'energy' placed?

You have two descriptions, phase and group velocity, describing a wave.
As far as I understand that include the whole wave approach?
Well that and the frequency:)

Phase velocity is the one giving a FTL 'look a like' if I get it right.
And group velocity is the one carrying the 'information' here.
That one (group velocity) won't ever travel faster than 'C' in space.

It's easier to understand the concept of 'energy' when looking at photons as particles to me.
But when I look at it as waves I find the 'energy's focus' harder to define.
So I would really like to see the concept of red and blue shift explained.

Is that unclear?
 

Offline LeeE

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How do photons lose energy?
« Reply #13 on: 08/02/2009 01:21:50 »
I don't understand this answer relating to referential frames. The photon has less energy now than it one did, if I measure it. So where is that missing energy?

Chris

It isn't missing, you just haven't accounted for the fact that you are moving away from the source of the photon; the energy that appears to be missing is accounted for in your velocity away from the photon's source.  If you were approaching the photon's source instead of receding from it, you'd think it had gained energy rather than losing it.

Yor_on; you write some interesting stuff but I find it very difficult to read because you seem to be inserting a newline/return at the end of each sentence.  When I try to read this my eyes keep on having to jump back and forth across the screen, which tires them, and I keep losing my place in your text, making it difficult to keep track of what you're saying.

No offence intended, and you can format your posts however you like, but bare in mind that if you want people to read what you write you should try to make it easy for them.
 

Offline Vern

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How do photons lose energy?
« Reply #14 on: 08/02/2009 01:30:52 »
Quote from: yor_on
Vern, if you look at it as a wave instead of particles then where are the (light quanta's) 'energy' placed?


A photon is both a wave and a particle; we all know that; but we all do not agree upon just how to visualize that. I like to visualize things in physics. Most physicists like to make principles and laws and theories and not visualize them. So you hear things like; nothing can go faster than light because of the theory of relativity. That is completely wrong. Things can't go faster than light because of some fundamental property of the things. The theory of relativity just describes the process.

So when I visualize a photon; I can visualize it as both a particle and a wave at the same time. All I need do is consider it as being two electromagnetically saturated points surrounded by electric and magnetic fields that extend outward from the points forever into space.

The fields give me the wave; the points give me the particle. There are many other benifits
that derive from the vision. For example, I can know the fundamental cause of relativity phenomena. I can answer the question: What is mass? And many others.

 
« Last Edit: 08/02/2009 01:35:21 by Vern »
 

Offline yor_on

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How do photons lose energy?
« Reply #15 on: 08/02/2009 02:09:04 »
Ok Vern, point taken.
I know that you define it both ways.

But I would like to see a 'main stream' view too.
Is there anyone who would like to describe red and blue shift.

using words :)
As waves using frame_A frame_B?

----

LeeE, I'm just used to write that way, it may be a bad habit but:)
I find it easier to see how I thought when I 'chop' it up.
Maybe you're right though?
« Last Edit: 08/02/2009 02:15:07 by yor_on »
 

Offline Vern

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How do photons lose energy?
« Reply #16 on: 08/02/2009 02:22:20 »
Quote from: yor_on
But I would like to see a 'main stream' view too.
Is there anyone who would like to describe red and blue shift.
I don't think I was deviating from the mainstream view when I described the red and blue shift. It if is Doppler, it is because the light originated in something that is moving relative to us. If it is moving away, it will be red shifted because a light wave takes time to form. As the wave develops, the originator moves away, so the peaks and troughs must spread further apart.

That seems like a simple concept; are you having trouble with that?
 

Offline yor_on

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How do photons lose energy?
« Reply #17 on: 08/02/2009 02:40:00 »
Vern I can describe it that way too, but I still can't visualize how the 'energy' is thought to be delivered.

And speaking about trouble:)
When I find myself confused I'm afraid I get like a bull terrier, I get stuck until I'm through::))

This is what really made me start to wonder though.

"If we imagine the wave profile as a solid rigid entity sliding to the right, then obviously the phase velocity is the ordinary speed with which the actual physical parts are moving.

However, we could also imagine the quantity "A" as the position along a transverse space axis, and a sequence of tiny massive particles along the x axis, each oscillating vertically in accord with A0 cos(kx - wt). In this case the wave pattern propagates to the right with phase velocity vp, just as before, and yet no material particle has any lateral motion at all.

This illustrates that the phase of a traveling wave form may or may not correspond to a particular physical entity. It's entirely possible for a wave to "precess" through a sequence of material entities, none of which is moving in the direction of the wave. In a sense this is similar to the phenomenon of aliasing in signal processing.

What we perceive as a coherent wave may in fact be simply a sequence of causally disjoint processes (like the individual spring-mass systems) that happen to be aligned spatially and temporally, either by chance or design, so that their combined behavior exhibits a wavelike pattern, even though there is no actual propagation of energy or information along the sequence."

http://www.mathpages.com/HOME/kmath210/kmath210.htm
 

Offline Vern

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How do photons lose energy?
« Reply #18 on: 08/02/2009 03:44:39 »
Okay; this is much more clear and I agree with you. There need not be the physical movement of any material thing for the wave to progress. And as at least one of our local peers suggests there might need not be anything happening between the originating event and the observing event when a photon goes from place to place. But I need to think more on this to even get a visual image of it in my mind.

Any thing we can contrive to explain a present observation must also be compatible with all the past observations that have ever been made. So I think of the Fourier transforms and how barriers placed in the path of light cause distortions and wonder whether that means that there must be some electromagnetic disturbance that is physically present in the space between the source of light and the detector.

So; I am learning; I hope. But I do find some very interesting ideas abounding here.
 

Offline LeeE

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How do photons lose energy?
« Reply #19 on: 08/02/2009 12:30:43 »
Yor_on, I don't see it as being right or wrong;  You have a perfect right to say what you want in the way that you want to say it, but I do think it's true that if you want people to read what you say you should try to make it easy for them.  I do want to read what you say, but sometimes find it harder work than it need be.
 

Offline Vern

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How do photons lose energy?
« Reply #20 on: 08/02/2009 15:16:40 »
Okay; it is a new day and maybe thought will happen a little better now. On the matter of whether a red shifted photon has lost energy; if it is the result of Doppler shifting, it has not. The photon is the same as it always was.

If the red shift is the result of Halton Arp's Tired Light scheme, then the photon has lost energy. In this case the thing from which the photon came need not be moving away. This is the scenario I like. I like it mainly because we need not dispose of the physical laws of nature if that is the case. If we like alternative views, we immediately introduce an avalanche of problems with the physical laws which seem to contradict the views.
« Last Edit: 08/02/2009 15:23:37 by Vern »
 

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How do photons lose energy?
« Reply #21 on: 09/02/2009 17:02:13 »
LeeE, I will test:)

But I'm not sure it will be easier to read, the type of English I really like to write is the one with all those 'strange' words, eloquent sort of. I'm quite in love with the richness of the English language:) which doesn't necessarily mean that it gets more understandable.

And then there is English English, (New Hebrides English, Falklands English, Hong Kong English, Irish English, Scottish English), Australian English, New Zealand English, Indian English, American English.

I guess that list can go on for quite a bit, I've probably missed quite a lot of countries. So English have a lot of different 'traditions' when it comes to how to express and use it:)

That's what makes it into one of the most important languages today. Once you had Latin (Europa), but now I would say it's English.
« Last Edit: 09/02/2009 17:08:06 by yor_on »
 

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How do photons lose energy?
« Reply #22 on: 09/02/2009 17:22:03 »
Yes Vern, if that idea would be right the photon would become easier to understand. But you know that I'm a 'follower' of Einsteins model. And there he describes photons as being 'time less' internally.

There are arguments against 'tired light' that makes sense to me, one need to see that some build on other main stream assumptions though, but they all seem to fit together. I have this link http://www.astro.ucla.edu/~wright/tiredlit.htm that discuss some of the arguments against.
 

Offline LeeE

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« Reply #23 on: 10/02/2009 17:21:18 »
Yor_on:  I found that really easy to read and understand:)  The sentences that related to each other were grouped together and so the relation, and therefore meaning, between them was clear to me.

Certainly use exotic or strange words - they're fun - and carry on trying to be eloquent too, as eloquent writing is a pleasure in itself to read.
 

Offline Vern

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How do photons lose energy?
« Reply #24 on: 10/02/2009 18:01:34 »
Quote from: yor_on
There are arguments against 'tired light' that makes sense to me, one need to see that some build on other main stream assumptions though, but they all seem to fit together. I have this link http://www.astro.ucla.edu/~wright/tiredlit.htm that discuss some of the arguments against.
I notice that Halton Arp seems to have abandoned the Tired Light model. His latest articles offer a new explanation. I'm not sure I can sign on to his latest scheme which proposes that the matter in newly created galaxies is less energetic.

I agree there are some very convincing arguments for an expanding universe.
 

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