February 10, 2019
A simple method for measuring the speed of a moving car is based on the Doppler effect. Since the car moves in the stationary system of the radar, the problem is identical whether it is considered classical or relativistic. No "time dilatation" can occur because the radar wave is only reflected by the moving vehicle and the number of waves reaching the vehicle must be equal to the number of waves bouncing off the vehicle. The waves cannot disappear on the way and no new waves can be created by bouncing off the mirror (the car behaves like a mirror). The same number of waves that are reaching the vehicle must return to the receiver. In the case of police radar, Einstein's second postulate and the classical wave theory are identical and must therefore both lead to the same result.