What happens when a single atom emits a single photon? Does the photon itself exist as a spherical wavefront that propagates in all directions? Or is it ejected as a tiny, "vibrating ball"? In other words, is the spherical wavefront of a light source (like a star) just the result of the composite effect of a bunch of linear "rays", or is there something fundamental about spherical EM propagation? From http://en.wikipedia.org/wiki/Electromagnetic_radiation -- What does it mean that "a single photon is sent through two slits"? I would also like to know just what kind of "wave" people are referring to when they talk about EM wave-particle duality. The only kind of spatial wave that I can imagine propagates spherically: either through a torsional action (transverse) or a compression-decompression action (longitudinal). Are there any sources out there where someone has attempted to give an explicit "geometric face" to the propagation of EM energy, at the most fundamental level?