
#1
Mar3104, 09:36 AM

P: 1

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 text books. 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??




#2
Mar3104, 06:54 PM

HW Helper
P: 2,327

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. 



#3
Apr104, 06:39 AM

P: 179

http://www.kevin.harkess.btinternet....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. 


#4
May1504, 10:18 PM

P: n/a

Photon Doppler Shift???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. 


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