- #106
PAllen
Science Advisor
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It seems the basic absurdity with @Speady 's argument has not been raised. The statement
The italicized part of this argument would apply exactly as stated for blue light versus red light for flash bulbs, stationary with respect to some detector. Does @Speady believe different colors of light travel at different speeds? I hope not, and the resolution is that the wavelength of a pulse is different. Doppler changes the wavelength of a pulse exactly inversely to frequency change. A shorter wavelength divided by a shorter duration, then produces exactly same speed. The key point is simply that red light doppler shifted to blue has all the same properties as blue light directly emitted as blue, including shorter wavelength. Quite frankly, the misunderstanding here is one that would be surprising even for someone with no background beyond a typical high school physics discussion of waves.
Speady said:Is it enough if c is not constant ?! When I approach a light source, the frequency increases, but the duration of the pulse that passes also becomes shorter. Conversely, the frequency decreases when removed, but the duration of the pulse also becomes longer. The same pulse passes me in a shorter and longer time. This is only possible if the speed of light (the pulse) (relative to me) becomes higher and lower.
The italicized part of this argument would apply exactly as stated for blue light versus red light for flash bulbs, stationary with respect to some detector. Does @Speady believe different colors of light travel at different speeds? I hope not, and the resolution is that the wavelength of a pulse is different. Doppler changes the wavelength of a pulse exactly inversely to frequency change. A shorter wavelength divided by a shorter duration, then produces exactly same speed. The key point is simply that red light doppler shifted to blue has all the same properties as blue light directly emitted as blue, including shorter wavelength. Quite frankly, the misunderstanding here is one that would be surprising even for someone with no background beyond a typical high school physics discussion of waves.