Critical review of theory of measurement in quantum mechanics

A critical review of the theory of measurement in quantum mechanics is presented first, which is focused on the recent controversy between the von Neumann-Wigner theory and the ergodic amplification theory. Making the point clear through discussions on the controversy, we then describe a new version of the Machida-Namiki-Araki theory, as a solution of the problem, in which the macroscopic nature of measuring apparatus is explicitly formulated in a continuous direct sum of many Hilbert spaces and the unitarity of S-matrix of elementary interaction processes between object and apparatus systems is maintained. Within the framework of their theory, it is explicitly shown that the reduction of wave packet takes place even in the negative result measurement. (author)