The Schrödinger equation is approximate, in two important ways. First, it is based on nonrelativistic (Newtonian) mechanics, rather than on Einstein’s relativistic mechanics. Paul Dirac, in 1928, provided another equation for electron wave functions that obeys the assumptions of special relativity. Second, it does not contain the effects of quantum fluctuations, such as virtual photons, on the electrons. Nevertheless, the Schrödinger equation is accurate enough for most practical applications of quantum theory to chemistry, materials science, and biology, and it is the version of quantum theory that is usually adopted in treating those subjects.