THEORY OF THE DECOHERENCE EFFECT

A theory of the decoherence effect can be obtained by applying the pro jection method in the theory of irreversible processes. The procedure is shown specifically on a model, already general enough for covering all the previously known ones. Decoherence is found to be governed by a master equation, which is particulary simple when the existence of c onvenient collective observables yields a preferred basis for diagonal ization. A criterion is given for the existence of such ''microstable' ' observables. In the case of mechanical macroscopic bodies, this basi s exits and is given by the position coordinates in ordinary three-dim ensional space for the various parts of the bodies.