The clack of two billiard balls signifies the transference of their momentum and the mathematics of resulting vectors is fairly straight forward. At the quantum level, I understand that the transfer of momentum is carried out by photon interactions. This would mean a lot of photons interacting and somehow, in sum, conserving of the classical momentum vectors. If there are no red flags in the above, I would appreciate guidance to a reference that explains the process in more detail, particularly the conservation of momentum. I would guess that each photon interaction must somehow convey vector information.