Hello, I wonder how the speed of interaction affects the energy levels in atoms. We know that electrons in atom are attracted to the protons in the nucleus through the electromagnetic force. Photon, the force carrier for the electromagnetic force, moves in empty space with the speed c (the speed of light). My question is: if the speed of interaction would have been different than c, let's say Fc (F>0), how this would affect the atoms and energy levels in atoms? Can someone re-calculate one energy level using Fc instead of c, and then compare the result with the normal energy level (the one with c as the speed of interaction)?