Dynamical interpretation for the quantum-measurement projection postulate

An apparatus model with discrete momentum space suitable for the exact solution of the problem is considered. The special Hamiltonian of its interaction with the object system under consideration is chosen. In this simple case it is easy to illustrate how difficulties in constructing the dynamical interpretation of selective collapse can be overcome without any limiting procedure. For this purpose one can apply either averaging with respect to a nonquantum parameter or reduce the algebra of joint-system operators (i.e., pass from an algebra A of operators to a subalgebra A(0)). The latter procedure implies averaging with respect to apparatus quantum variables not belonging to A(0).