Symposium on the Foundations of Modern Physics 1993 : Quantum Measurement, Irreversibility and the Physics of Information : Cologne, Germany, 1-5 June 1993
This volume offers discussions on foundational problems of quantum mechanics and other fundamental physical theories, taking into account new experimental developments. The surveying of the progress with respect to fundamental questions of the quantum theory of measurement forms the guiding line of thought of this Symposium, the main themes of discussion being: the inter-relation of quantum measurement and irreversability; the physics of information (concerned with questions of information processing and quantum noise); quantum interference and mesoscopic quantum effects (searching for the micro-macro borderline); and the quantum-classical relationship (the need for classical pointer and their realization).
This volume offers discussions on foundational problems of quantum mechanics and other fundamental physical theories, taking into account new experimental developments. The surveying of the progress with respect to fundamental questions of the quantum theory of measurement forms the guiding line of thought of this Symposium, the main themes of discussion being: the inter-relation of quantum measurement and irreversability; the physics of information (concerned with questions of information processing and quantum noise); quantum interference and mesoscopic quantum effects (searching for the micro-macro borderline); and the quantum-classical relationship (the need for classical pointer and their realization).
Although it is 70 years old, there are still areas of quantum theory which are open to interpretation. This book deals with such interpretational problems, and in particular with the issue of the measurement process. The main theme is whether quantum mechanics can be viewed as a (semantically) complete theory, namely as a theory capable of describing not only the physical object under observation but also the measuring instruments used to detect the properties of that physical object. The problematic aspects arise from the fact that the measuring instruments themselves behave as classical physical systems. Thus, we are faced with the open problem of the transition from the quantum to the classical, or more explicitly, the problem of why the composition of many quantum micro-objects gives rise to classical macro-objects. This book goes carefully, exhaustively, and deeply into the interpretational problems of quantum mechanics induced by the measurement process. The solution of many relevant issues, as well as the problems that remain unsolved, emerge clearly. The discussion itself is self-contained and the technical parts are reader-friendly. This book is of value to graduate students and researchers who have an interest in the physical, mathematical, and philosophical foundations of quantum mechanics.
Modern studies of basic quantum concepts and phenomena, E.B. Karlsson and E. Brandas quantum entanglement - criteria and collective tests, A. Peres a gallery of quantum states -tomography of nonclassical light, J. Mlynek et al experimental and theoretical progress in interaction-free measurements, P.G. Kwia entanglement, mesoscopic superpositions and decoherence studies with atoms and photons in a cavity, S. Haroche quantum coherence with a single Cooper pair, V. Bouchiat et al mesoscopic physics and the fundamentals of quantum mechanics, Y. Imry decoherence, chaos, quantum-classical correspondence and the algorithmic arrow of time, W.H. Zurek quantum entanglement - a fundamental concept finding its applications, A. Zeilinger quantum communication in a quantum network, J.I. Cirac et al. (Part contents).
Ever since the beginning of quantum mechanics, the measurement problem has been a subject of sometimes discontinued but nevertheless recurrent concern. As students, most physicists have raised questions about it, but the spectacular and renewed successes of quantum theory were a strong incentive for them to work out applications without further worrying about foundations. In each generation, however, some dissatisfaction reemerges, which leads to slow progress, and we may expect that the measurement problem will some day be cleared up rather than forgotten. The situation recalls statistical mechanics, the foundations of which still give rise to scientific discussions, in spite of more than one century’s achievements. Actually, the paradoxes of irreversibility and of Maxwell’s demon share some common features with quantum measurements, to wit, they involve probabilities in a crucial fashion and their explanation requires elucidating the role of the observer.
This paper discusses questions concerning the foundations of quantum mechanics (entanglement, wave collapse, irreversibility) with reference to the issues raised during a Minisymposium held in Helsinki, 1.6-3.6 in 1992, where A Shimony, A Peres and B d'Espagnat were invited to lecture. The measurement problem is related to the phenomenon of irreversibility which is known not to follow from any fundamental theory; e.g., the law of exponential decay does not follow from the Schrödinger equation in senso stricto. The approximations that lead to irreversibility are related to some form of ''forgetting'', or coarse graining. Some approaches to the question, why these approximations can be justified, are reviewed. The paper also discusses dynamical reduction schemes and it is suggested, that the corresponding non-linear modifications of the Schrödinger equation -- which lead to non-conservation of energy -- are actually ''effective'' Schrödinger equations for open systems (in analogy with the ''effective'' Lagrangians in QFT). Thus these modifications should be derived from a fundamental theory of interactions. The paper ends with some brief comments on the mind-body question in the quantum mechanical context. A postscript has been added (2006).
Introduction In this chapter I attempt to review a few somewhat loosely connected themes, which figure in recent work by physicists on decoherence and irreversibility in quantum mechanics. The looseness is forced upon us by the subject – any proper discussion inevitably drags in questions about thermodynamic reversibility and the various arrows of time, about the foundations of quantum mechanics and quantum measurement, about the nature of quantum coherence, and about the relationship between quantum and classical mechanics. There are inevitably many gaps in our understanding of these questions, both for the physicist and for the philosopher. Some philosophers may feel that the subject is too immature to be interesting to them – that it is not yet ripe for philosophical analysis. Indeed I have recently heard the opinion expressed that quantum mechanics in its entirety was still not amenable to such analysis – that if the physicists could not yet understand it, there was no point in philosophers trying! I hope this feeling is not too widespread amongst philosophers of science – I suspect that it may arise in part because the philosophical community (along with a good part of the scientific community) is unaware of some important advances that have been made in the last decade in understanding the physics of quantum processes at the macroscopic level, as well as the relation between classical and quantum mechanics. Much of the chapter is therefore unashamedly tutorial in nature; however, given the wide range of topics covered, I imagine that even physicists will find at least some of the material to be novel.