Quantum profiles and paradoxes

Abstract

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 Schr\"odinger 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 Schr\"odinger equation -- which lead to non-conservation of energy -- are actually ''effective'' Schr\"odinger 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).