# Is the classical Doopler Effect, for light shift, 1−v/c , exact? What is it an approximation of?

Marcelo Mullins 2022-07-23 Answered
Is the classical Doopler Effect, for light shift, $1-v/c$, exact? What is it an approximation of?
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Seromaniaru
He is comparing $\sqrt{\frac{1-v}{1+v}}$ to the classical Doppler shift $\left(1-v\right)$ (where $v$ is the velocity divided by $с$, since use units where $c=1$). The formula you give $\frac{1-v}{1+v}$ doesn't have a classical interpretation, and Einstein reduces to Doppler's at slow speeds.