There is an old joke about telling the police officer who stops you for running a red light that you were moving so fast that the light looked green. Take red to have a wavelength of 650 nm and green 500 nm. How fast WOULD you have to be moving (c = speed of light)? Is this relativistic?

Question

Quizplus · Accepted Answer

To observe the red light as green due to the Doppler effect, the required speed is relativistic. The shift from 650 nm to 500 nm due to relativistic Doppler effect implies a significant fraction of the speed of light, around 64% of c, confirming the relativistic nature of the scenario.

There Is an Old Joke About Telling the Police Officer