As far as I know, the evidence of expansion has everything to do with light. It's the Doppler effect. There is an apparent red shift (expansion of wavelengths) if you are moving away from the source, and a blue shift (compression of wavelengths) if you are moving towards the source. We see everything around us as red shifted, so it looks like we are raisins in a loaf of expanding bread. All raisins are moving away from each other, or the space in between raisins is expanding.