Quantum theory of the interactions of charged particles with the electromagnetic field .
It describes the interactions of light with matter as well as those of charged particles with each other. Its foundations were laid by quantum mechanics and the theory of special relativity . The theory, as refined and developed in the late 1940s, rests on the idea that charged particles interact by emitting and absorbing {{link=photon">photons . It has become a model for other quantum field theories .