Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

Is the classical doopler effect for light shift equal to $1-v/c$ exact or an approximation of a classical formula? I know that it is an approximation of the relativistic formula, but what was the corresponding classical formula? I ask this because in Einstein's On the Electrodynamics of moving bodies he derives $\sqrt\frac{1-v/c}{1+v/c}$ and notes that it is different from the classical case. I'm not exactly sure what formula he is comparing it to.

share|improve this question
    
Classical mechanics is the approximation of relativistic mechanics when the speed involved is small compared to that of light. –  C.R. May 28 '12 at 2:41
    
Doppler, not doopler... –  WIMP May 28 '12 at 7:14
add comment

1 Answer 1

up vote 1 down vote accepted

He is comparing $\sqrt{1-v\over 1+v}$ to the classical Doppler shift $(1-v)$ (where v is the velocity divided by c, since I use units where c=1). The formula you give $1-v\over 1+v$ doesn't have a classical interpretation, and Einstein reduces to Doppler's at slow speeds.

share|improve this answer
    
Thanks. I thought there was another, more exact, classical formula. –  MadScientist May 31 '12 at 4:07
    
@BarryBarrett: What would it be? You can do a weird transformation of space and time in 1+1d space with right-moving light which keeps distances unstretched and keeps the speed of right-moving light constant, but this is just a mathematical trick, it has no physical significance. –  Ron Maimon Jun 1 '12 at 6:12
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.