 The pilot-wave approach to quantum theory was initiated by Einstein, even before the discovery of quantum mechanics itself. Einstein hoped that interference phenomena involving particle-like photons could be explained if the motion of the photons was somehow guided by the electromagnetic field—which would thus play the role of what he called a Führungsfeld or guiding field (see Wigner [1976] 1983: 262 and Bacciagaluppi and Valentini 2009: Ch. 9). While the notion of the electromagnetic field as guiding field turned out to be rather problematical, Max Born explored the possibility that the wave function could play this role, of guiding field or pilot wave, for a system of electrons in his early paper founding quantum scattering theory (Born 1926). Heisenberg was profoundly unsympathetic. 