ABSTRACT
This chapter examines the reasons why measurement theory is a particularly controversial part of modern theoretical physics. The problem of measurement in quantum mechanics is considered as nonexistent or trivial by an impressive body of theoretical physicists and as presenting almost insurmountable difficulties by a somewhat lesser but steadily growing number of their colleagues. The law of evolution in time constitutes the essential part of the conventional measurement theory. In this theory, the existence of a Hamiltonian describing the instrument-system interaction is postulated, not derived. In other words, this assumption is considered as a legitimate idealization of the experimental facts. A wave packet reduction can be considered as a phenomenological procedure that, in many instances, can be applied in order to calculate the results of successive observations and the correlations between them without introducing into the formulas the complicated wave functions of the various instruments.
