Later Criticism of the Copenhagen Interpretation

Badis Ydri

H. Capellmann

Vladislav E. Terekhovich

The centenary of quantum mechanics brings into focus the question of the accuracy of established terminology for describing the radical transformations that occurred. Critical analysis reveals that the term “quantum revolution” fosters a simplified perception of a single, pivotal turn in physics during the 1920s and 1930s and provides a superficial account of the actual changes over the past 100 years. This article critically re-examines the established term “quantum revolution” from the perspective of its conceptual limitations in describing the real changes of the last century. Arguments are presented for its partial replacement with the more flexible concept of “revolutionary transformations in quantum theory and its interpretations”, which emphasises the processual and multifaceted nature of these changes. The methodological foundation of this research is the distinction between two types of interpretations of quantum theory: “pragmatic” interpretations, which focus on connecting the formalism with experiment, and “explanatory” interpretations, which aim to form conceptions of quantum reality. The application of the concept of a quantum revolution is justified for the pragmatic interpretation, which was formed in 1925–1927 and later became established as the orthodox view, but not for interpretations of the explanatory type. Three initial strategies for preserving classical language in the description of quantum phenomena are identified: classical realism, quantum dualism, and instrumentalism. The analysis addresses persistent historiographical myths surrounding the Copenhagen interpretation – namely, that it is inherent in the postulates of quantum theory, and that it is inherently instrumentalist and subjectivist. A distinction is shown between the orthodox (pragmatic) and the Copenhagen (explanatory) interpretations. Particular attention is paid to the realistic turn in explanatory interpretations (1952–1958), largely associated with the later works of Heisenberg. It is concluded that the development of quantum theory is characterised not by a single revolution, but by a series of transformations of varying revolutionary intensity, many of which occurred in parallel and are still far from complete.

M. V. Lokajíček, V. Kundrát, J Procházka

The assumptions added by Bohr and concerning the Hilbert space (formed by all solutions of Schroedinger equation) changed fundamentally the original physical interpretation of these solutions proposed earlier by Schroedinger. This new alternative was refused by Einstein on the basis of the EPR Gedankenexperiment, but accepted fully for microscopic reality by scientific community. Both the quantum alternatives were discussed, however, again later. Bell tried to find a possibility how to decide between them; he generalized Einstein's Gedankenexperiment assuming that also spins of two detected particles would be measured. He derived then some inequality for a special combination of four coincidence probabilities, and it was commonly assumed that his inequality held for the original Schroedinger interpretation but not in Bohr's Copenhagen quantum mechanics; without any actual proof having been given. Corresponding experiments were proposed and finished in 1982. The violation of Bell's inequality was then interpreted as decisive victory of Bohr's theory. However, it will be shown that Bell's inequality has been interpreted mistakenly. It has been based always on some assumption that does not hold in any probabilistic theory (i.e., in the given spin experiment) but only in deterministic classical theory. There is not any argument for preferring the Copenhagen quantum mechanics and against Einstein's critical standpoint. Some other consequences will be mentioned, too.

Arthur I. Miller

Norwood Russell Hanson

The theoretical and experimental context within which the “Copenhagen Interpretation” of quantum theory was generated is underemphasized by recent critics of the Bohr-Heisenberg philosophy. When an interpretation of a theory has been as successful as this one has been, there is little practical warrant for the “alternative interpretations” which have, since Bohm, been receiving prominence. Indeed, these are not even genuine alternatives; although rich in provocative prose, they provide not a scrap of algebra with which to organize the practical physicist's thinking. Several objections to the Bohr interpretation are critically examined, as is also a particular use of the correspondence principle which has seemed to cast doubt on the Copenhagen ideas.