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Originally Posted by papageno
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Originally Posted by lyndonashmore
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Originally Posted by papageno
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Originally Posted by lyndonashmore
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Originally Posted by papageno
At length-scales much larger than the average distance between particles, one sees a density of charges, not single charge carriers.
The density is nearly unifrom, because of the relatively high speed and random motion of the electrons.
An electromagnetic wave with a wavelength comparable to these length-scales, does not interact with one electron at a time, but with a high number of electrons at the same time.
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And what do these electrons do when the wave interacts with them?
I mean how do they move? |
At those length-scales, talking about motions of single electrons is not very helpful, which is why you always find the charge density in your sources. |
But it is helpful to me. |
Because you do not actually perform proper calculations. |
I will accept a 'hands in packets' none hand waving qualititive answer from you here Papageno.
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Originally Posted by lyndonashmore
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If you treat the electromagnetic wave as a macroscopic oscillating electric field, the single electron is accelerated.
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As it is accelerated what does it do, What path does this acceleration cause the electron to follow?
A wave is a predictable thing, so we must be able to determine the effects of the acceleration on the electron. |
If you treat the electron as a classical particle, the acceleration is in the direction of the force.
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In e-m waves the force varies periodically so are you now saying that this electron performs SHM in a classical sense?
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Originally Posted by lyndonashmore
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Originally Posted by papageno
If you treat it as a collection of photons, you have lots of electron scattering lots of photons.
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So how do we get a density wave - a predictable thing with a calculable frequency if the electrons are all scattering the photons randomly? |
As the name says, you use the charge density for the calculations.
If there is an external electric field, the motions are nearly random.
Add up enough nearly random motions and, if they are correlated, you can end up with a not-so-random density oscillation.
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What is 'nearly random' is it something superimposed on top of their random motion to make their motion nearly random?
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Originally Posted by lyndonashmore
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Originally Posted by papageno
(An electron oscillates in a high-power laser light, because it is scattering a lot of photons: for each photon it recoils, and adding up all the recoils, you end up with an oscillation. This is Feynman's picture in his QED book, as far as I understand.)
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A laser beam travelling from left to right can only cause the electron to recoil from left to right.
How does 'adding up all these recoils' cause it to 'oscillate back and forth'? |
There is no reason for the recoil to be limited along the direction of propagation.
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True but can the photons 'suck' the electrons backwards?
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Originally Posted by lyndonashmore
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Originally Posted by papageno
But in your "theory" you try to explain the red-shift as a sum of single-electron/single-photon scattering, which is not the same as macroscopic electormagnetic waves and plasma oscillations.
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Macroscopic effects are the net result of microscopic effects. |
If you studied solid state physics, you would know things can be more complicated (see many-body effects).
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I thought we had already agrred on this - I did.
Cheers
Lyndon