[KayEyeDoubleDee]

This may be a silly question. It's been a while, but ...

Does we actually understand why the red shift exists? I remember talking to some physics grad students (I was a lowly math/physics undergraduate at the time) who said that no one really understood why there was a red shift, as opposed to the Doppler effect which clearly exists because there is a medium in which the waves are being produced, and against which the source moves. There is no medium for light, ie. no ether if you believe Michelson/Morley.

[KayEyeDoubleDee]

as opposed to the Doppler effect for sound waves

[Physicist]

But the point is that there is a Doppler effect for light whether there's a medium or not. Measuring redshifts and blueshifts for radio waves and laser beams is something students do in undergraduate labs. It's a stone cold experimental fact that if something is moving away from you, its light is demonstrably and reproducibly redshifted. So we can explain the redshift of distant objects without invoking exotic new physics, simply by making the assumption that they are moving away from us.