Dopler Shift and Photon Number

  • Thread starter cmos
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  • #1
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Main Question or Discussion Point

Here's something that I recently thought about:

If we assume a Doppler shifted EM wave retains the amplitude of the unshifted wave, then we must be creating/annihilating photons. This seems consistent with the conservation of energy; the removal of several photons removes energy from the system but this energy is conserved by the increase in energy of the remaining photons, as would be the case of a blue shift.

Does this seam reasonable?

I realize that number conservation of photons is never a requirement, but it originally bothered me that photons can just come in and out of existence in the manner described above. My explanation for this is that during a Doppler shift, a single photon is either joining with several others or splitting into several others in a manner that conserves energy.

Does this seem reasonable?
 

Answers and Replies

  • #2
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Probably a good idea to look into coherent states and bogoliubov transformations.
 
  • #3
clem
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The Doppler shift does not change the number of photons.
The frequency, energy and momentum of each photon changes.
 
  • #4
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The Doppler shift does not change the number of photons.
The frequency, energy and momentum of each photon changes.
If the number of photons does not change, then a change in wavelength will induce a change in amplitude. For the amplitude to remain the same, the number of photons must change - hence my original post.

lbrits, I will be looking into it.....
 
  • #6
clem
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If the number of photons does not change, then a change in wavelength will induce a change in amplitude. For the amplitude to remain the same, the number of photons must change - hence my original post.
lbrits, I will be looking into it.....
Why do you assume the amplitude won't change? The E and B fields change in a Lorentz transformation.
Consider light so weak that there is only one photon.
Could a small change in frequency add or subtract a photon?
 

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