The special relativity theory owes its origin principally to Maxwell's theory of the electro-magnetic field. This explains why his 1905 paper on relativity was entitled: "On the Electrodynamics of Moving Bodies." "Electrodynamics" is the study of electric and magnetic forces, and in this paper Einstein was concerned with explaining the way that electric and magnetic fields act on moving charges and especially how these various actions are interrelated. He combined this with the empirical fact that there does not exist any physically distinguishable state of motion which may be called "absolute rest." The theory also discarded the absolute character of the conception of the simultaneity of two spatially separated events.