Interaction between classical and quantum systems

An unconventional approach to the measurement problem in quantum mechanics is considered. The apparatus is treated as a classical system, belonging to the macro-world. In order to have a measurement the apparatus must interact with the quantum system. The classical apparatus is embedded into a large quantum mechanical structure, making use of a superselection principle. The apparatus and system are coupled with such that the apparatus remains classical (principle of integrity), and unambiguous information of the values of a quantum observable are transferred to the variables of the apparatus. Thus interactions causing pointers to move can be added. The restrictions placed by the principle of integrity on the form of the interaction between classical and quantum systems are examined and illustration is given by means of a simple example in which one sees the principle of integrity at work.