I'm very curious as to what actually causes light to bend when it encounters a medium with a different refractive index. Of course the speed of light changes, and this speed change is accompanied by a corresponding wavelength change so that the frequency remains the same and there is no discontinuity at the interface between media... but why does the light also change direction? And the fact that the direction change is specific and always occurs is interesting. Do we have any understanding as to why light will always bend toward the normal when entering a higher RI medium? And why is it only when light impinges upon a different medium at an angle? For instance, light striking a surface orthogonally does not change direction. Thank you very much!