The measurement problem of quantum mechanics

The measurement problem of quantum mechanics is the problem of reconciling the change of state of a system described by the dynamical group of the theory. The author deals with the difficulties in the way of the hidden-variable interpretation and considers both the Copenhagen and van Neumann interpretations. He argues that there is an aspect of the measurement problem, referred to as the statistical problem of measurement, which is properly resolved by interpreting the projection postulate as the probability conditionalization rule appropriate to a non-Boolean possibility structure of events, or noncommutative algebra of random variables. He discusses the semantic problem of measurement and abstracts two opposing directions for a solution to this problem. (Auth.)