  We show that the key problems of quantum measurement theory, namely the
reduction of the wave packet of a microsystem and the specification of its
quantum state by a macroscopic measuring instrument, may be rigorously resolved
within the traditional framework of the quantum mechanics of finite
conservative systems. The argument is centred on the generic model of a
microsystem, S, coupled to a finite macroscopic measuring instrument, I, which
itself is an N-particle quantum system. The pointer positions of I correspond
to the macrostates of this instrument, as represented by orthogonal subspaces
of the Hilbert space of its pure states. These subspaces, or 'phase cells', are
the simultaneous eigenspaces of a set of coarse grained intercommuting
macroscopic observables, M, and, crucially, are of astronomically large
dimensionalities, which incease exponentially with N. We formulate conditions
on the conservative dynamics of the composite (S+I) under which it yields both
a reduction of the wave packet describing the state of S and a one-to-one
correspondence, following a measurement, between the pointer position of I and
the resultant state of S; and we show that these conditions are fulfilled by
the finite version of the Coleman-Hepp model.
