ABSTRACT

According to Niels Bohr quantum theory must be interpreted, not as a description of nature itself, but merely as a tool for making predictions about observations appearing under conditions described by classical physics:

Strictly speaking, the mathematical formalism of quantum theory … merely offers rules of calculation for the deduction of expectations about observations obtained under well-defined conditions specified by classical physical concepts. 1

There can be no question of any unambiguous interpretation of the symbols of quantum mechanics other than that embodied by the well-known rules which allow to predict the results to be obtained by a given experimental arrangement described in a totally classical way. 2

This necessity of discriminating in each experimental arrangement between those parts of the physical system considered which are treated as measuring instruments and those which constitute the object under investigation may indeed be said to form a principal distinction between classical and quantum description of physical phenomena. 2

Indispensable use of classical concepts … even though classical physical theories do not suffice. 2

This indispensable use of the invalidated classical concepts is a troublesome point. So is the intrusion into the theory of the scientist himself; the scientist must make a somewhat arbitrary division of a single unified physical system into two separate parts, and describe them according to mutually incompatible physical theories.