Photon Doppler Shift: Exploring the Theory

In summary: Wolfgang Rindler's "Relativity: Special, General, and Cosmological" (2001). I'm pretty sure he says something about the doppler shift.
  • #1
ckirksey
1
0
Photon Doppler Shift?

I am a practicing EE who has used the standard Doppler shift equation for thirty years in radar design; therefore, I am not disputing the correctness of the equation but the "explanation" that is so often given in textbooks. The general explanation always discusses relative velocity between source and receiver. I have always wondered how the "photon" that was emitted or absorbed "knew" the relative velocity in question. The pictorials always describe the wavefronts being bunched closer or further apart as the source/receiver moves. But at the time of emission or absorption how does the photon know its velocity?? And relative to what?? The effect is such that on the relative velocity is important but the explanation of how this info is imparted to the photon leaves a lot to be desired. If anyone on this forum has a good reference to this I would greatly appreciate hearing about it. My own thoughts are that there is a background FOR to which all source/receiver velocities are referenced. It is the difference in the effects that the velocity relative to this FOR has on the photon that is eventually made known at the receiver. The FOR maybe unnecessary from the point of view of SR but the explanantion of how this relative velocity info is imparted to the photon is surly lacking. Also could this be a case for the quantum mechanical argument that it is only observables that are important in a theory since one can really only measure energy of the photon directly??
 
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  • #2
ckirksey said:
I have always wondered how the "photon" that was emitted or absorbed "knew" the relative velocity in question.
...
... at the time of emission or absorption how does the photon know its velocity?? And relative to what??
Light travels at c in both the transmitter's and the receiver's rest frames. It is the transmitter that "knows" to emit at c, and it is the receiver that "knows" to receive at c. Don't blame the poor innocent photon. :wink:




ckirksey said:
If anyone on this forum has a good reference to this I would greatly appreciate hearing about it.
There are hundreds of treatments by hundreds of authors on common theoretical applications of SR. Try Wolfgang Rindler's "Relativity: Special, General, and Cosmological" (2001) I'm pretty sure he says something about the doppler shift.




ckirksey said:
My own thoughts are that there is a background FOR to which all source/receiver velocities are referenced.
Basically, an ether? This is not believed to be the case. And I'm pretty sure that the doppler shift formula that you have is not compatable with that notion. Check it against the first semester physics doppler shift for sound, which does propagate through an absolute FOR.




ckirksey said:
The FOR maybe unnecessary from the point of view of SR ...
Actually, the way you described it, not only is it unecessary, but completely imcompatable with the fundamental premise of SR.




ckirksey said:
Also could this be a case for the quantum mechanical argument that it is only observables that are important in a theory since one can really only measure energy of the photon directly??
I don't think so, but that is just MHO. In the QM context, observable indicates a Hermitian operator, in other words, having a measurement that results in purely real vs. complex/imaginary numbers. I don't think that this is the same kind of "observable" that you are talking about regarding the transmission and reception of E&M radiation.




Try this:

I'm assuming that you're familiar with Maxwell's equations. Well, you can get a wave equation from them that has a propagation constant that shows up. These equations are believed to be valid regardless of how fast you are traveling WRT some arbitrary FOR, with the condition that you are approximately in an inertial frame. Since this is the case, that constant is assumed to be just that, a constant.

So, applying this idea to the transmitter, it uses Maxwell's equations with that constant to transmit the E&M radiation. The receiver is sitting there and all of a sudden starts experiencing E&M waves. These satisfy Maxwell's equations at the receiver, so, they also have that same constant.

That propagation constant is c.
 
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  • #3
ckirksey said:
The general explanation always discusses relative velocity between source and receiver. I have always wondered how the "photon" that was emitted or absorbed "knew" the relative velocity in question. The pictorials always describe the wavefronts being bunched closer or further apart as the source/receiver moves. But at the time of emission or absorption how does the photon know its velocity?? And relative to what?? The effect is such that on the relative velocity is important but the explanation of how this info is imparted to the photon leaves a lot to be desired. If anyone on this forum has a good reference to this I would greatly appreciate hearing about it. My own thoughts are that there is a background FOR to which all source/receiver velocities are referenced.

I believe you're right. For a full set of Doppler equations that explain this in terms of an ether frame of reference, see section 9.3 / equation set 9.6
http://www.kevin.harkess.btinternet.co.uk/wisp_ch_9/wisp_ch_9.html

If the motion of the source relative to the ether is 0, then the equations become those of SR. I would be interested to know if using these equations in your work gives better results or the same results as SR?
If you need help with the time dilation terms, let me know.
 
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  • #4
ckirksey said:
I am a practicing EE who has used the standard Doppler shift equation for thirty years in radar design; therefore, I am not disputing the correctness of the equation but the "explanation" that is so often given in textbooks.


My own thoughts are that there is a background FOR to which all source/receiver velocities are referenced.


You are absolutely correct.

Are you aware that under the Doppler Law, there are TWO causes of redshifts and blueshifts?

1) “Stretched out” or “compressed” waves due to the motion of the emitter.

and,

2) A faster or slower relative speed of the wave, relative to the observer, due to a moving observer.
 

1. What is the Photon Doppler Shift theory?

The Photon Doppler Shift theory is a scientific concept that explains the change in frequency or wavelength of light as it moves towards or away from an observer. This shift in wavelength is caused by the relative motion between the source of light and the observer.

2. How does the Photon Doppler Shift theory work?

The Photon Doppler Shift theory is based on the principle of the Doppler effect, which states that the frequency of a wave will change depending on the relative motion between the source and the observer. In the case of light, this results in a change in the wavelength of the light as it moves towards or away from the observer.

3. What are the applications of the Photon Doppler Shift theory?

The Photon Doppler Shift theory has many practical applications in various fields such as astronomy, telecommunications, and remote sensing. It is used to study the motion of celestial objects, measure the velocity of objects in space, and even in medical imaging techniques like Doppler ultrasound.

4. How is the Photon Doppler Shift theory different from the Doppler effect?

The Photon Doppler Shift theory is a specific application of the general Doppler effect, which describes the change in frequency or wavelength of any type of wave, while the Photon Doppler Shift theory specifically refers to the change in wavelength of light. Additionally, the Photon Doppler Shift theory takes into account the fact that light travels at a constant speed, while the Doppler effect can apply to any type of wave.

5. Can the Photon Doppler Shift theory be observed in everyday life?

Yes, the Photon Doppler Shift theory can be observed in everyday life. An example of this is the redshift and blueshift of light from moving objects, such as the changing pitch of a siren as a police car passes by. It is also used in technologies like GPS, where the change in frequency of light is used to measure the speed and position of moving objects.

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