
#1
Nov1705, 04:09 PM

P: 4

Hey, sorry if this is a stupid question but I'm getting really confused...
If I am standing on the Earth and watch a spaceship moving past at say 0.8*c from left to right, I will observe the spaceship to contract in its direction of motion. If a person on the spaceship shines a torch also from left to right, what happens to the wavelength of the light as seen from my reference frame? Does it also contract? 



#2
Nov1705, 04:50 PM

Sci Advisor
P: 8,470

To compare the wavelength you see with the wavelength seen by the shipobserver, just divide [tex](c \pm v)/(f \sqrt{1  v^2/c^2})[/tex] (the wavelength seen by you) by c/f (the wavelength seen by the shipobserver), which gives [tex](1 \pm v/c) / \sqrt{1  v^2/c^2}[/tex] for the factor that the wavelength changes in your frame. This is not the same as the Lorentz contraction factor [tex]\sqrt{1  v^2/c^2}[/tex]. 


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