A process predicted to occur in quantum electrodynamics (QED) that does not occur in classical electrodynamics. Light scattering by light does not occur in classical physics because Maxwell's equations are linear, whereas electrodynamics becomes nonlinear when quantum effects are taken into account. The process has never been conclusively observed but powerful lasers may enable it to be observed in the future. Light scattering by light was first predicted in the 1930s, when calculations of the process were performed by the German physicist Werner Heisenberg and others. Complete calculations of light scattering by light were not performed until the renormalization of QED was developed in the late 1940s.