>>11488386Why not? You can "explain" it using quantum mechanics, but it's not really going to tell you anything new or interesting that the classical picture didn't already give you. In fact, the reason is almost trivially so: the state of the light undergoing refraction is classical itself (either a coherent state or a thermal state), so of course the process admits a classical description. Even the process of the electrons' dipole moments in the medium being oscillated to create the additional, interfering waves can be described by classical Lorentz oscillators.
Of course, the pedant will ask why the material is made up of billions of little Lorentz oscillators, and where did this "electric charge" thing come from anyway, which trivially requires QM to "explain". But similarly you would also say, where did electromagnetic waves come from, if not as a macroscopic manifestation of excitations in the quantum mechanical EM modes? So in that sense you might "always" need QM to explain literally any phenomenon. But that's a rather unhelpful philosophy to take. If the classical theory is sufficient to explain observed experimental data, then we use it until we reach the boundary of its domain of applicability.
