This is a follow-up of the following thread on refraction: https://www.physicsforums.com/showthread.php?t=576212&highlight=photon In a nutshell, an optical photon that traverses a solid dielectric extends over many atoms. While the photon traverses the dielectric, it continuously transmits some of its energy into a forced oscillation of charges which return the energy by emitting secondary waves (perhaps better to say wavelets) with a slight, progressive phase delay. The result is a delayed photon. However, in post #19 the following question came up: Indeed, it is no conceptual problem for those of us who regard a photon as a kind of wave packet, and the Planck energy as the characteristic energy of emission and detection. However, it may be a problem for those who regard a photon as an indivisible particle, and/or the Planck energy as a true atom of energy, independent of observation. With such an interpretation, how does one explain refraction?