An effect predicted to occur in quantum electrodynamics in which electron–positron pairs are ‘sucked out’ of a vacuum by an electric field. This effect, predicted in 1951 by the US physicist Julian Schwinger, has never been observed since it is extremely small but it is thought that it could be observed with a sufficiently large electric field. A possibility is that it could occur in heavy ion reactions. The Schwinger effect can be thought of as analogous to field emission in metals.