In what way is a reflected photon degraded?

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Offline MikeS

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In what way is a reflected photon degraded?
« on: 31/10/2011 08:16:19 »
A reflected photon imparts pressure to the reflecting surface.
This would imply that work has been done.
The photon has not been absorbed but it has been degraded by the loss of energy in some form.
In what way is the photon degraded by the loss of energy?

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Offline Soul Surfer

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In what way is a reflected photon degraded?
« Reply #1 on: 31/10/2011 12:07:29 »
Work is done only if the surface actually moves. In most cases of most surfaces the collisions are perfectly elastic the surface does not move as a whole and so no energy is lost.  The same would be true for grains of dust etc. Even when photons of light are reflected or scattered by individual atoms the atoms are much heavier than the momentum of the photons and scattering is usually elastic see Rayleigh Scattering  however this may not be the case particularly for higher energy photons and energy will be lost  see Compton scattering.

An interesting aside.  In general for higher energy photons like gamma rays the reaction of the emitting nucleus causes a spreading of the wavelength  however there are some cases where the nucleus is effectively locked into the structure by quantum effects and the energy of the photon is incredibly precise and this can be used for very accurate measurements foe example the gravitational red shift caused by the earth's gravity.  this is called The Mossbauer effect.
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Offline simplified

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In what way is a reflected photon degraded?
« Reply #2 on: 31/10/2011 16:44:17 »
A reflected photon imparts pressure to the reflecting surface.
This would imply that work has been done.
The photon has not been absorbed but it has been degraded by the loss of energy in some form.
In what way is the photon degraded by the loss of energy?
In your case:
E -lost energy
m' - zero mass of photon = hν/c
m - mass of surface
c -  speed of light
                         E=2(m')c/m

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Offline Bored chemist

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In what way is a reflected photon degraded?
« Reply #3 on: 31/10/2011 21:35:21 »
The photons can lose energy when they bounce off things, but the effect is usually only noticeable when the things are small.
http://en.wikipedia.org/wiki/Compton_scattering
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Offline MikeS

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In what way is a reflected photon degraded?
« Reply #4 on: 02/11/2011 07:11:27 »
Thanks guys but I don't think your replies really answers the question "In what way is the photon degraded by the loss of energy?"

A photon can not loose energy by slowing down and as I understand it, it is not red-shifted.  So what is happening?  Could it be that some photons are being reflected with no energy transfer and some are being absorbed?

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Offline Soul Surfer

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In what way is a reflected photon degraded?
« Reply #5 on: 02/11/2011 15:38:38 »
if a photon loses energy it is red shifted  or more accurately absorbed and remitted with a lower energy with the result that the particle it hit moves off with the energy deficit in a direction associated with the absorbed and emitted photons
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Offline yor_on

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In what way is a reflected photon degraded?
« Reply #6 on: 02/11/2011 18:32:36 »
I'm not sure I get this one? Are you suggesting that photons don't get absorbed by a mirror but instead are 'reflected'? There are two ways to describe it, and using a wave picture is the oldest one and also the one we easiest recognize. The other is a particle picture in where the photons get absorbed by the mirrors atoms, most releasing new photons, that over a broad distribution presents us with the angles of reflection we associate with a wave. Although some of the explanations to how a 'photon' is expected to do so seem to be connected to the the way a wave interfere, quenching and reinforcing, via 'frequencies' which, as far as I know, no 'photon' is expected to have in a particle picture, frequency that is. Another way to define their angles 'reflecting' might be the momentum they have and how that gets 'mirrored' by the atom creating new photons.
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Offline Soul Surfer

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In what way is a reflected photon degraded?
« Reply #7 on: 03/11/2011 08:58:43 »
I was referring to MikeS's statement a photon is not red shifted when it is involved in nonelastic scattering.  You seem to have a hangup about the wave/particle duality it is a true duality photons always have the full properties of both. Can you not think of a wave packet?   true as the photon energy rises it is easier to think of them as particles.  Processes inside the limits of quantum uncertainty cannot be observed it is only the results that matter
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Offline MikeS

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In what way is a reflected photon degraded?
« Reply #8 on: 04/11/2011 09:08:42 »
If it's a perfectly reflecting surface, presumably there would be no loss.  The photon being absorbed and re-emitted at the same frequency and the surface recoiling in the process.  This would imply a gain of energy, so it can't happen.  But what is happening?  Is the photon red-shifted by being reflected by a perfectly reflecting surface?  Can a photon be absorbed and re-emitted by a perfectly reflecting surface?  If the surface is perfectly reflecting how can it absorb the photon?  If it's a perfectly reflecting surface does the photon impart any energy to that surface?
Thanks

Soul Surfer
Having read your previous replies I can't see how Rayleigh Scattering could be the answer as it applies to transparent objects.
« Last Edit: 04/11/2011 12:44:08 by MikeS »

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Offline Soul Surfer

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In what way is a reflected photon degraded?
« Reply #9 on: 05/11/2011 00:20:24 »
Consider a largely but not perfectly reflecting heavy surface.  If a photon strikes the surface it can be either reflected or absorbed by the surface.  A photon has both energy and momentum if it is absorbed the energy in the photon warms the surface which could cause another photon of lower energy to be emitted.  If it is reflected the photon is unchanged except that its direction of travel has changed and therefore its momentum has changed so the law of conservation of momentum applies and some momentum has been given to the surface.  Note the momentum of a photon is very much less than its energy (a factor of the speed of light).  An illustration of this process is given in the behaviour of the Crookes radiometer.  as the pressure in the tube is reduced from lowish to a hard vacuum.

Why do you think that Rayleigh scattering only applies to "transparent " objects?
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Offline MikeS

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In what way is a reflected photon degraded?
« Reply #10 on: 05/11/2011 08:41:51 »
Consider a largely but not perfectly reflecting heavy surface.  If a photon strikes the surface it can be either reflected or absorbed by the surface.  A photon has both energy and momentum if it is absorbed the energy in the photon warms the surface which could cause another photon of lower energy to be emitted.  If it is reflected the photon is unchanged except that its direction of travel has changed and therefore its momentum has changed so the law of conservation of momentum applies and some momentum has been given to the surface.  Note the momentum of a photon is very much less than its energy (a factor of the speed of light).  An illustration of this process is given in the behaviour of the Crookes radiometer.  as the pressure in the tube is reduced from lowish to a hard vacuum.

Why do you think that Rayleigh scattering only applies to "transparent " objects?

Soul Sufer
Thanks for reply.  I had been trying to find information on the Crooks radiometer but couldn't as I didn't know what it was called.  Interesting, I always thought it operated directly by radiation pressure but apparently its a heat engine.

I didn't know anything about Rayleigh scattering so did a quick internet search and it seemed to only be happening in transparent mediums like gasses.

"If it is reflected the photon is unchanged except that its direction of travel has changed and therefore its momentum has changed so the law of conservation of momentum applies and some momentum has been given to the surface." 
But "if some momentum has been given to the surface" then surely, the photon can not be "unchanged". It would have to be re-emitted at a lower frequency in order to conserve energy. Or, if it were reflected unchanged, then it can't have transferred any energy to the reflecting surface. ??????

We know that the reflected photon does not loose energy (red-shift).  So does it impart momentum to the reflecting surface?  Or is it only absorbed photons that impart momentum?
« Last Edit: 05/11/2011 09:01:25 by MikeS »

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Offline Soul Surfer

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In what way is a reflected photon degraded?
« Reply #11 on: 05/11/2011 18:09:32 »
Even individual atoms are too heavy to allow a normal light photon to loose a significant amount of its total energy and momentum
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Offline MikeS

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In what way is a reflected photon degraded?
« Reply #12 on: 06/11/2011 10:48:40 »
Even individual atoms are too heavy to allow a normal light photon to loose a significant amount of its total energy and momentum

But my point is any transference of energy and momentum, no matter how small must show as a change in the photons energy for the law of conservation of energy to hold.

This is a quote about solar sails.
"How does light push a solar sail?
Photons, which are "particles" of light, bounce off the reflective material of the sail. (Newton's Third Law of Motion states that for every action there is an equal and opposite reaction.) The reaction here causes a change in momentum, pushing the sail and accelerating the spacecraft. A photon reflecting off the mirror-like surface of a solar sail gives the sail a double kick -- a push equal to twice the photon's momentum (one push from the sail stopping the photon and one from it reflecting the photon and accelerating it away)."

http://www.discoversolarenergy.com/solar/sails.htm

The photon is reflected essentially unchanged, it still has the same energy.  So where has the energy imparted to the sail come from?

If we bounce light backwards and forwards between two parallel mirrors it does not loose energy by becoming red-shifted and yet the mirrors get a slight push on every reflection.

Here is another article on solar sails.
"Sailing Motion
Sailing motion is determined by theta, the angle between the solar radial and the ship's total force vector.  A positive theta generally adds energy and causes outward motion.  A negative theta generally reduces energy and causes inward motion.  The projection of the acceleration vector onto the velocity vector determines the actual change in energy in the local gravitational field.  A sail does not extract energy from or put energy into the reflected light to accomplish its sailing.

If the reflection does not extract energy from or inject energy into the photons, how does the sailing ship gain or lose energy? The reflected photons have the same energy flux they had prior to the interaction, but a different momentum vector. It is this altered momentum vector that gives the ship an accelerating force that allows it to work against the gravitational field to gain or lose energy within the field. The absorbed photons are the energy lost from the impinging flux. The absorbed energy is re-radiated from the sail, with some helping and some hindering the ships motion."

http://sail.quarkweb.com/light.htm

I believe this is saying that the altered momentum vector of the photons is where the force that causes the acceleration comes from.  In other words the force comes from the change in direction (through rebound) of the photons (Newtons third law...)  That still doesn't explain why the sail can gain energy if the reflected photons don't loose any.

Does anyone know of any experimental evidence confirming that reflected photons do exert a 'push'?

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Offline simplified

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In what way is a reflected photon degraded?
« Reply #13 on: 06/11/2011 12:07:59 »
p=mc
2p=2mc
(2mc/mc)*100%≈0% of energy  [:P]

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Offline JP

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In what way is a reflected photon degraded?
« Reply #14 on: 06/11/2011 14:20:54 »
Mike, if the photon gives up some of it's energy, it will rebound with a smaller frequency.  Generally they give so little energy to atoms or molecules that it's negligible.  With a solar sail, radiation pressure is also tiny, but there is a huge number of photons bouncing off it for a long period of time and no friction to slow it down, so these tiny pushes keep adding up.

The push of reflected photons can be measured, and I know of a bunch of experiments that measure it in one way or another, usually in a lab with laser light.  There is already one functioning solar sail, as well: http://en.wikipedia.org/wiki/IKAROS

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Offline MikeS

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In what way is a reflected photon degraded?
« Reply #15 on: 07/11/2011 09:03:20 »
Mike, if the photon gives up some of it's energy, it will rebound with a smaller frequency.  Generally they give so little energy to atoms or molecules that it's negligible.  With a solar sail, radiation pressure is also tiny, but there is a huge number of photons bouncing off it for a long period of time and no friction to slow it down, so these tiny pushes keep adding up.

JP
I understand all of the above but I don't understand how a reflected photon can give up none of its energy (see my last post above) but still give a small push to the reflecting surface.  This would seem to imply an increase of energy which can't be the case as it would break the law on conservation of energy.

This makes me question whether a reflected photon can impart any momentum to the reflecting surface, or is it only absorbed photons that can do this?

Any experiment to measure the push of a reflected photon must involve a significant number of photons and can we be certain that all the photons have been reflected not absorbed?  As no mirror is perfect we can't be certain.  If an experiment were able to confirm that the push was twice as much for a reflected photon as an absorbed photon then it would be evidence confirming the hypothesis.  I have not been able to find any evidence of such an experiment.  If you know of any links I would appreciate you posting them.

It's been proven that solar sail technology is possible and we are told it is due to the push given by reflected photons bouncing off the mirror and the mirror recoiling but how can we be certain that it is not due to absorption? 

(Aside.  If it is from absorption then there could also be a small contribution from the forces that power a Crookes radiometer.  Presumably (?) if a solar sail works by reflection then it is not a heat engine but if it works by absorption then it is.)

Thanks for your time.

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Offline yor_on

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In what way is a reflected photon degraded?
« Reply #16 on: 07/11/2011 09:51:41 »
Well, yeah :)

I'm afraid I still think of it as a 'duality', although I can see why people jump from a photon to 'frequency', it's not the same to me. It's a weird subject though.

Both answers correct in century-old optics dilemma.
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Offline simplified

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In what way is a reflected photon degraded?
« Reply #17 on: 07/11/2011 14:03:54 »
Mike, if the photon gives up some of it's energy, it will rebound with a smaller frequency.  Generally they give so little energy to atoms or molecules that it's negligible.  With a solar sail, radiation pressure is also tiny, but there is a huge number of photons bouncing off it for a long period of time and no friction to slow it down, so these tiny pushes keep adding up.

The push of reflected photons can be measured, and I know of a bunch of experiments that measure it in one way or another, usually in a lab with laser light.  There is already one functioning solar sail, as well: http://en.wikipedia.org/wiki/IKAROS
I know when the solar sail can be very effective.We should send a rocket to a comet.Then the rocket should travel on the comet till the maximal speed of the comet. Then the rocket should fly up from the comet and release a solar sail. A high-speed object receives more energy of photons, therefore such rocket can travel to the nearest stars. [:)]
Maybe the rocket can recieve the same speed without comet. [:-\]
« Last Edit: 09/11/2011 12:56:39 by simplified »

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Offline JP

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In what way is a reflected photon degraded?
« Reply #18 on: 07/11/2011 14:13:57 »
Mike, if the photon gives up some of it's energy, it will rebound with a smaller frequency.  Generally they give so little energy to atoms or molecules that it's negligible.  With a solar sail, radiation pressure is also tiny, but there is a huge number of photons bouncing off it for a long period of time and no friction to slow it down, so these tiny pushes keep adding up.

JP
I understand all of the above but I don't understand how a reflected photon can give up none of its energy (see my last post above) but still give a small push to the reflecting surface.  This would seem to imply an increase of energy which can't be the case as it would break the law on conservation of energy.


It should give up some of its energy, and its frequency does change.

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Offline MikeS

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In what way is a reflected photon degraded?
« Reply #19 on: 09/11/2011 09:23:29 »
If light bouncing back and forth between two mirrors looses its energy (as generally believed) by becoming red-shifted then this should be visible and measurable.  But in multiple reflections there does not appear to be any red-shift, instead the light gradually becomes dimmer.  This would seem to indicate that that the light is not loosing energy by being reflected but by absorption as the mirrors are not perfectly reflecting.

If anyone knows of any links to experimental evidence, one way or another, please post them.  Thanks

My own feelings are that reflected light does not impart momentum to the mirror and so is not red-shifted.
Light reflected by two perfectly reflecting mirrors would essentially last unchanged indefinitely, were it not for photons escaping through quantum tunnelling.  I appreciate this view may be wrong but would like to see the evidence.

More confusion here
http://www.physicsforums.com/archive/index.php/t-3647.html

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Offline yor_on

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In what way is a reflected photon degraded?
« Reply #20 on: 09/11/2011 10:41:40 »
I don't think there ever will be perfectly reflecting mirrors Mike. But assume there was, then they would have to 'reflect' perfectly too. Maybe that's the reason there can't be :)

Anything interacting with something else must impart a momentum, and lose some of its 'energy' in form of? Heat? and maybe 'something else' too? I don't know there. I'm still too hung up on the idea of usable 'energy' versus 'used unusable energy' to really make up my mind on that one. But if it 'interacts' it will lose 'energy'.
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Offline simplified

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In what way is a reflected photon degraded?
« Reply #21 on: 09/11/2011 12:52:04 »
If photon gives more momentum to a mirror,then this photon gives less energy to the mirror. [;)]

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Offline JP

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In what way is a reflected photon degraded?
« Reply #22 on: 09/11/2011 13:25:16 »
Mike, I can't tell you about any experiments but I can tell you that energy and momentum are conserved.  That's a fundamental law, even in quantum mechanics.

Light does impart momentum to the mirror by conservation of momentum.  If the mirror moves as a result of that momentum, then the photon has to redshift.  I suspect this redshift can be thought of as the doppler shift, since the reflected photon is coming off a moving mirror.  Obviously the amount the mirror moves from one photon is infinitesimal, so the redshift is as well.

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Offline simplified

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In what way is a reflected photon degraded?
« Reply #23 on: 09/11/2011 14:05:46 »
Mike, I can't tell you about any experiments but I can tell you that energy and momentum are conserved.  That's a fundamental law, even in quantum mechanics.

Light does impart momentum to the mirror by conservation of momentum.  If the mirror moves as a result of that momentum, then the photon has to redshift.  I suspect this redshift can be thought of as the doppler shift, since the reflected photon is coming off a moving mirror.  Obviously the amount the mirror moves from one photon is infinitesimal, so the redshift is as well.
Yes,then imparted momentum < 2p

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Offline yor_on

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In what way is a reflected photon degraded?
« Reply #24 on: 09/11/2011 14:43:25 »
That's a tricky one. In my book it loses 'energy' by losing momentum. To assume otherwise is to define momentum as something else than 'energy'. But momentum will transfer a 'energy' if we define it as the ability to do work, and transform. So, I don't think you can do that, differ them.

"In empty space, the photon moves at c (the speed of light) and its energy and momentum are related by E = pc, where p is the magnitude of the momentum vector p. This derives from the following relativistic relation, with m = 0

    E2 = p2c2 + m2c4."

Also take a look at How Does the Total Energy of a Particle Depend on Momentum. 
=

Which then, if we apply it on the concept of a time less, mass less, photon implies that photons then can 'change energy' intrinsically :) (when 'reflected' from a mirror) I don't think so.

When we instead look at it as a wave?

"Minkowski's formulation, on the other hand, seems more natural from the point of view of quantum mechanics. As light slows down inside a medium its wavelength also decreases, but quantum mechanics tell us that shorter wavelengths are associated with higher energies, and therefore higher momenta. In fact, Minkowski's approach suggests that the momentum of a single photon of light increases by a factor n as it passes through a medium. This result can also be supported by strong theoretical arguments, among them one that considers what happens when an atom moving at some speed through a medium absorbs a photon and experiences an electronic transition."

And as a wave it should also interact, as it will pass glass in and back out, and so get a 'higher momentum' :) Eh, in a ordinary mirror that is.

But assume just a (perfectly) reflecting surface, no glass involved. Then, if it is true that wave can't lose 'energy' due to reflection we can let it reflect between two mirrors into infinity, so, will it lose momentum then? If we now assume that momentum is different from the concept of 'energy'?

Einstein used E=mc2, there mass is assumed to be 'E = energy'. Which in physics is the same 'm'  you multiply the velocity by, to find a momentum (p). Light use "m" because of its energy, not (invariant) rest mass.
« Last Edit: 09/11/2011 15:41:46 by yor_on »
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Offline simplified

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In what way is a reflected photon degraded?
« Reply #25 on: 09/11/2011 14:58:41 »
That's a tricky one. In my book it loses 'energy' by losing momentum. To assume otherwise is to define momentum as something else than 'energy'. But momentum will transfer a 'energy' if we define it as the ability to do work, and transform. So, I don't think you can do that, differ them.

I can't, but ability to impart momentum is not ability to impart energy. [:P]

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Offline JP

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In what way is a reflected photon degraded?
« Reply #26 on: 09/11/2011 15:29:45 »
Energy and momentum are not the same thing by any definition.  Momentum is given by three numbers and energy by one number for starters.

Now, under some conditions, you can use conservation of energy/momentum/mass to figure out one from the other, but that doesn't mean they're the same thing.

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Offline yor_on

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In what way is a reflected photon degraded?
« Reply #27 on: 09/11/2011 15:39:51 »
Well, I'm saying that momentum becomes 'energy' in its transformation/interaction. Am I wrong?
=

Then again, thinking of a 'light wave' and trying to see its momentum becomes really tricky as one prefer to define a momentum to something specific, like a 'photon/particle'. So how do quantum mechanics find the momentum for a standing wave? Its 'energy' alone. And how about a wave existing 'everywhere'? Where is the momentum?

It's a weird subject :)
« Last Edit: 09/11/2011 15:51:42 by yor_on »
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Offline JP

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In what way is a reflected photon degraded?
« Reply #28 on: 09/11/2011 15:50:01 »
What do you mean by its transformation?  Isn't that assuming it's becoming something that isn't momentum?  It should always stay momentum, and momentum in = momentum out.

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Offline yor_on

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In what way is a reflected photon degraded?
« Reply #29 on: 09/11/2011 15:53:47 »
Well, if you want to define it as something not being 'energy', then it has to transform into 'energy' when interacting. As long as I'm thinking right here that is. But I agree, that wasn't the best formulation, interaction is clearer.
=

What I mean is that 'momentum' is an expression of energy, and I find it very hard to see it any other way. But then we have interactions, in where the energy expressed will belong to to both particles interacting. When light blue shift/red shift it is a consequence of interactions, that is two 'frames of reference' 'communicating', as in that light being annihilated on your retina, not an expression of a 'photon' changing energy intrinsically.
« Last Edit: 09/11/2011 16:09:14 by yor_on »
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Offline yor_on

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In what way is a reflected photon degraded?
« Reply #30 on: 09/11/2011 15:59:59 »
Would you expect the momentum to stay the same (for the wave)? Isn't the conservation law implied for the whole 'system', not the reflected wave. That is, the momentum, counting in both mirror and wave, is unchanged?

Or is it something else you mean?
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Offline simplified

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In what way is a reflected photon degraded?
« Reply #31 on: 09/11/2011 16:30:49 »
Would you expect the momentum to stay the same (for the wave)? Isn't the conservation law implied for the whole 'system', not the reflected wave. That is, the momentum, counting in both mirror and wave, is unchanged?

Or is it something else you mean?
was p + 0
      then -p + 2p
« Last Edit: 09/11/2011 16:40:04 by simplified »

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Offline JP

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In what way is a reflected photon degraded?
« Reply #32 on: 09/11/2011 16:31:47 »
Momentum of the whole system stays the same in the interaction.
Energy of the whole system stays the same in the interaction.

That's why you can't transform one to the other.  If momentum somehow transformed into energy, you'd violate conservation of both energy (you'd gain some) and momentum (you'd lose some).  What can happen is that different parts of the system gain or lose energy/momentum, but the total in the system has to stay constant for both energy and momentum, independently.

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Offline yor_on

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In what way is a reflected photon degraded?
« Reply #33 on: 09/11/2011 16:49:22 »
Yes, that's how I understands it. Transform here is my way of saying what you define as, gain or lose 'energy'. But it's the interaction creating it, not some magical, each one by themselves, 'happening' :)

Didn't know you couldn't use the word transform for this btw. Would it be wrong to say that radiation transforms into energy too?
=

Perhaps convert would be more acceptable :)
« Last Edit: 09/11/2011 16:52:53 by yor_on »
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Offline JP

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In what way is a reflected photon degraded?
« Reply #34 on: 09/11/2011 18:20:51 »
Well, like everything else in science, precision is king.  If you're precise about what you mean by transform, it's fine to use it in a scientific context. 

But yes, in interactions particles can transfer energy or momentum.  It's possible for this energy and momentum to create new particles as well.

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Offline JP

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In what way is a reflected photon degraded?
« Reply #35 on: 09/11/2011 23:53:52 »
Also, it's worth checking out these three pages on wikipedia.  They go into details about how elastic scattering of light from an electron (i.e. it doesn't lose energy) is just a limit of the more general scattering where the energy loss is so small that it can be neglected:
http://en.wikipedia.org/wiki/Thomson_scattering
http://en.wikipedia.org/wiki/Compton_scattering
http://en.wikipedia.org/wiki/Klein-Nishina_formula

The last link actually provides the quantum model that extends from the elastic limit to the inelastic limit.

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Offline MikeS

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In what way is a reflected photon degraded?
« Reply #36 on: 11/11/2011 08:57:41 »
Thinking about it, presumably a photon can not be reflected.  To be reflected there would have to be a point at which it was stopped.  If not reflected then it must be absorbed and another photon re-emitted.

There seems to be two trains of thought on this.
One, the photon is re-emitted at the same frequency, in which case it cannot have imparted any momentum to the mirror.
Two, the photon imparts momentum to the mirror and another photons is re-emitted at a lower frequency.
Either way the 'reflected' photon does not impart any momentum to the mirror as there is no reflection.  The photons impart momentum on absorption and again on re-emission.  The more reflective the surface, the higher the frequency of the re-emitted photon.

If the above is correct then solar sails do not work by reflecting light but by absorbing and re-radiating it.
What's wrong with this argument?

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Offline yor_on

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In what way is a reflected photon degraded?
« Reply #37 on: 11/11/2011 09:14:12 »
What hurts me head here is the assumption that a interaction can leave what interacts untouched. In this case 'photons' bouncing of a mirror. So maybe you can differ a photons momentum from 'energy', although I don't see how. No, on second thought, I don't think you can. To use the idea of them 'bouncing' and keeping their energy, and then say it is proved by the way photons don't redshift ignore the fact that they are constantly sent out from a source, get annihilated at a sink, and re-emitted depending on their 'energy' relative what they annihilate against. What is even more irritating is 'proving' it using wave functions. It's rather naive to define a duality from one point of view solely, as long as there is no experimental proof of one side of it being secondary and dependent on the first. I won't do that.

I still think of it as a duality, not a wave packet.
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Offline yor_on

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In what way is a reflected photon degraded?
« Reply #38 on: 11/11/2011 09:24:42 »
And a photon doesn't have a frequency, only a momentum and a energy. It is waves that have a frequency, and a wavelength. Ah, that also mean that a individual 'photon' can't red shift, only 'waves' do that. And even if considering them over a extended period of time passing some 'point', the photons passing when measured have not red shifted. There must be some underlying definition for how they express the duality, in different situations, but I don't think considering them as 'renormalized wavepackets' with arbitrarily made 'cutoffs' answer that one. There is something else governing the way they express themselves. There is something inherently wrong with any approach that need to lift out the 'wrong' numbers, to get to the right ones, we see experimentally.
« Last Edit: 11/11/2011 09:34:18 by yor_on »
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Offline JP

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In what way is a reflected photon degraded?
« Reply #39 on: 11/11/2011 14:27:26 »
Yor_on, photons do have a frequency.  They don't oscillate like classical waves, but they have a property called wavelength.  This is necessary, because when you add them up in the right way, this property is what creates a classical wave with a given wavelength.  That frequency, f, is also what gives them energy of hf. 

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Offline JP

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In what way is a reflected photon degraded?
« Reply #40 on: 11/11/2011 14:29:27 »
Mike, your reasoning is correct.  Reflection, absorption/re-emission and scattering from a mirror are all different words for the same phenomenon.  You can't reflect without giving up energy, but the usual assumption is that the energy loss is so small that it doesn't matter.

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Offline yor_on

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In what way is a reflected photon degraded?
« Reply #41 on: 11/11/2011 20:29:32 »
I don't know if I agree, I think of it as a duality? Maybe you are thinking of trapping photons in microwave cavities? How about Compton scattering, describing the opposite?

" The Compton effect is introduced in Gasiorowicz (in section 1.3, pages 7-9 in the 3rd edition, or pages 11-13 in the 2nd edition). The text describes the experimental discovery of the effect discovered by Arthur H. Compton - radiation of a given wavelength (in X-rays) sent through a foil was scattered in a manner inconsistent with classical radiation theory.

If one is dealing with elastic scattering,the system can be understood quantitatively as Thomson scattering. However, the Compton effect can be understood as photons scattering inelastically off individual electrons."

Here you start with x-rays, and end with 'photons'. Photoelectrons, Compton and Inverse Compton Scattering
« Last Edit: 11/11/2011 20:34:53 by yor_on »
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Offline JP

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In what way is a reflected photon degraded?
« Reply #42 on: 11/11/2011 21:03:25 »
You don't agree with what?

Photons have a frequency, which is true: E=hf after all.  If you want to know how this relates to the frequency of a classical wave, check out coherent states.  It takes a lot of math to prove it, but you can superimpose photons in such a way to make a classical wave of the same frequency as the photons: http://en.wikipedia.org/wiki/Coherent_states

Also, check my links above if you don't believe me that Compton and Thompson scattering are related.  The general quantum scattering problem is quite complex, but you can simplify it by assuming certain things, which is what is done in these two cases.  Thompspon scattering assumes that the photon loses so little energy that you can treat it as losing none and still get accurate results.
« Last Edit: 11/11/2011 21:07:39 by JP »

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Offline yor_on

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In what way is a reflected photon degraded?
« Reply #43 on: 11/11/2011 22:34:04 »
I don't agree to it being one or the other, to me radiation seems to define itself through the relations/interactions with what surrounds it in the measurement.
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Offline yor_on

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In what way is a reflected photon degraded?
« Reply #44 on: 11/11/2011 22:36:36 »
And no JP, they are related, the link I gave says it too.
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Offline JP

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In what way is a reflected photon degraded?
« Reply #45 on: 11/11/2011 23:58:26 »
So you're agreeing with me?

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Offline swadewade8

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In what way is a reflected photon degraded?
« Reply #46 on: 12/11/2011 04:26:39 »
Quote
A reflected photon imparts pressure to the reflecting surface.
This would imply that work has been done.
The photon has not been absorbed but it has been degraded by the loss of energy in some form.
In what way is the photon degraded by the loss of energy?

From what I have noticed throughout life is that whenever a force is exerted and deflected it does lose energy in some way.  Just as when light is deflected when bent through space as it is gravitationally bent as well considering how far stars are away from us.  A case in point would be the stars that we see at night and 'appear' to be in a fixed position in the sky.  Considering how far they are away, they may be a bit off from where they appear.  The closer the star of course the less it may be off, such as Alpha centauri the closest one to us if I recollect right.  The image is accurate of course, it just may not be exactly where we see it in space.  As far as my point goes, concerning loss of energy, have you ever known anything in life that that has a 'theoretical' constant velocity that didn't lose some type of momentum or energy when acted upon by some external force that is fixed?  One has to apply this formula when taking this aspect into consideration and make the assumption that this is equated in some way.   

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Offline yor_on

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In what way is a reflected photon degraded?
« Reply #47 on: 12/11/2011 13:41:51 »
I don't know how you see it? Most people today define it from waves, with photons becoming some sort of 'focus' for that. I don't think either one is perfect, on the other hand I can't say how it should work. My own, most unscientific opinion, is that both waves and 'photons' are a description of what relations there are defining them.

That doesn't necessarily demand a underlying 'reality' aka, some 'hidden' background, defining what they really, really, are. But I think it demand another way of looking at them, that make their duality a result of the demands, different in different experiments. So I'm happy with thinking of both as 'real', well, as real as we can define it. Which then means that I'm not convinced of anything :)
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Offline JP

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In what way is a reflected photon degraded?
« Reply #48 on: 12/11/2011 14:15:07 »
Ah, I think I understand you now.  Check out that link I posted above (http://en.wikipedia.org/wiki/Coherent_states).  It explains the precise mathematical connection between photons and waves.

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Offline yor_on

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In what way is a reflected photon degraded?
« Reply #49 on: 13/11/2011 14:51:50 »
Yep JP. it's better to discuss it from coherent states, that precludes any of our ideas on 'waves and 'photons'' But then I meet another problem. I do like indeterminacy (HUP), but I'm not sure I find 'virtual particles' as convincing. To me they are starting to become a figment of our deep conviction of thingies 'moving and propagating'. And I'm not sure what that is any more. Physics are truly confusing, reminding me of Pandoras box. You may open it, but on your own peril. There has to be a way of describing it not involving 'virtuality' as in something 'moving'.

And to me it must have to do with 'time'.

I prefer indeterminacy to 'virtual particles' those days
« Last Edit: 13/11/2011 14:54:35 by yor_on »
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