Dear All, I have read many posts on this forums about the interaction of photons with the atoms of transparent materials. The point that I was searching for in particular was "why is the speed of light in transparent material less than c". The explanations given by many about the absorption and re-emission of photons by the atoms are quite elaborate. However, there is no mention of scientific references for that theory. Can anyone, please, provide me with some references where this theory is explained. Thank you in advance for your help. Milad H.