Taking a new perspective provided by a generalization of the mathematical formalism encompassing positive operator-valued measures, this book views old and new problems of the foundations of quantum mechanics. It demonstrates the crucial role of the generalized formalism in fundamental issues and practical applications.

Taking a new perspective provided by a generalization of the mathematical formalism encompassing positive operator-valued measures, this book views old and new problems of the foundations of quantum mechanics. It demonstrates the crucial role of the generalized formalism in fundamental issues and practical applications.

After introducing the empiricist point of view in philosophy of science, and the concepts and methods of the semantic approach to scientific theories, Professor van Fraassen discusses quantum theory in three stages. He first examines the question of whether and how empirical phenomena require a non-classical theory, and what sort of theory they require. He then discusses the mathematical foundations of quantum theory with special reference to developments in the modelling of interaction, composite systems, and measurement. Finally, the author broaches the main questions of interpretation. After offering a critique of earlier interpretations, he develops a new one - the modal interpretation - which attempts to stay close to the original Copenhagen ideas without implying a radical incompleteness in quantum theory. He gives special attention to the character of composite, many-body systems and especially to the peculiar character of assemblies of identical particles in quantum statistics.

The author argues that quantum theory admits a plurality of interpretations, each aiding further understanding of the theory, but also advocating specifically the Copenhagen Variant of the Modal Interpretation. That variant is applied to topics like the Einstein-Podolsky-Rosen paradox and the problem of 'identical' particles.

Quantum mechanics is an extraordinarily successful scientific theory. But more than 100 years after it was first introduced, the interpretation of the theory remains controversial. This Element introduces some of the most puzzling questions at the foundations of quantum mechanics and provides an up-to-date and forward-looking survey of the most prominent ways in which physicists and philosophers of physics have attempted to resolve them. Topics covered include nonlocality, contextuality, the reality of the wavefunction and the measurement problem. The discussion is supplemented with descriptions of some of the most important mathematical results from recent work in quantum foundations, including Bell's theorem, the Kochen-Specker theorem and the PBR theorem.

Authored by an acclaimed teacher of quantum physics and philosophy, this textbook pays special attention to the aspects that many courses sweep under the carpet. Traditional courses in quantum mechanics teach students how to use the quantum formalism to make calculations. But even the best students - indeed, especially the best students - emerge rather confused about what, exactly, the theory says is going on, physically, in microscopic systems. This supplementary textbook is designed to help such students understand that they are not alone in their confusions (luminaries such as Albert Einstein, Erwin Schroedinger, and John Stewart Bell having shared them), to sharpen their understanding of the most important difficulties associated with interpreting quantum theory in a realistic manner, and to introduce them to the most promising attempts to formulate the theory in a way that is physically clear and coherent. The text is accessible to students with at least one semester of prior exposure to quantum (or "modern") physics and includes over a hundred engaging end-of-chapter "Projects" that make the book suitable for either a traditional classroom or for self-study.