If classical physics does not apply to light, then how is red shift possible?

Question

If the motion of an object that is the origin of light is irrelevent, how does the motion of galaxies result in a red shift as the are moving away from us?

Answer 1

The red shift is a result of decreasing frequency of the light, not its speed. It is just like a train passing you. As it comes toward you the sound gets higher and higher because their is less space between the pulses. When it passes you, the sound gets lower and lower as the space between pulses gets longer and longer. The speed of the train is still the same, its just that the frequency changes.