Born reciprocity

Born reciprocity is a principle in physics related to the behavior of systems under transformations involving the interchange of certain variables, particularly in the context of optics and electromagnetism. Named after the physicist Max Born, the concept often arises in discussions about wave propagation, diffraction, and the relationship between electric and magnetic fields. In its simplest form, Born reciprocity states that certain physical laws and relationships are invariant under the exchange of "source" and "field" variables.