https://www.physicsforums.com/showpost.php?p=899393&postcount=4 describes why photons are slower in some medium. After reading it, I've few more questions: When a photon hits an electron, if it absorbs the photon and reemits, here's my questions: 1. How does refraction possible? The electrons are moving around randomly. The photon that entered into the electron does not need to be reemitted in the same direction. But how are we able to see things? 2. How does reflection possible? The surface may look flat, but in a macroscopic level. But for a photon, it just hit a round oblect (nucleus or electron). To me, the coefficient of reflection in terms of angle of incidence does not make any sense in a particle level. Mathematically, to have an angle, you need 3 points. 2 points in the reflecting surface, one point for the photon. With these 3 points, you could say the photon hit the surface in an angle. But for a photon, it hit just one electron. It does not care about the other electrons in the surface. In that case, there is no 3 points, it is only 2 points. But then, how does the reflection work?