 Further along these lines, Zeh (2003b) argues that decoherence can explain the appearance of particle detections within quantum field theory (see the entry on  quantum field theory).  Therefore, only fields need to be included in the fundamental concepts, and ‘particles’ are a derived concept, unlike what might be suggested by the customary introduction of fields through a process of ‘second quantisation’. Another application to quantum field theory is the suggestion that the justification for the (strict) superselection rule for charge in quantum field theory can also be phrased in terms of decoherence. As pointed out by Giulini, Kiefer and Zeh (1995; see also Giulini et al. 1996, Section 6.4), an electric charge is surrounded by a Coulomb field (which electrostatically is infinitely extended; the argument can also be carried out using the retarded field, though). States of different electric charge of a particle are thus coupled to different, presumably orthogonal, states of its electric field. One can consider the far-field as an effectively uncontrollable environment that decoheres the particle (and the near-field), so that superpositions of different charges are indeed always  suppressed.[40]