ar X iv : q ua nt - p h / 02 11 02 1 v 2 3 A pr 2 00 3 Quantum Physics and Classical Physics - in the Light of Quantum Logic

In contrast to the Copenhagen interpretation we consider quantum mechanics as universally valid and query whether classical physics is really intuitive and plausible.-We discuss these problems within the quantum logic approach to quantum mechanics where the classical ontology is relaxed by reducing metaphysical hypotheses. On the basis of this weak ontology a formal logic of quantum physics can be established which is given by an orthomodular lattice. By means of theSoì er condition and Piron's result one obtains the classical Hilbert spaces.-However, this approach is not fully convincing. There is no plausible justification of Soì er's law and the quantum ontology is partly too weak and partly too strong. We propose to replace this ontology by an ontology of unsharp properties and conclude that quantum mechanics is more intuitive than classical mechanics and that classical mechanics is not the macroscopic limit of quantum mechanics. 1 The dualism of Copenhagen interpretation Even today, 75 years after the discovery of quantum mechanics many quantum physicists are convinced that the Copenhagen interpretation is still the right way for understanding quantum physics. According to this interpretation we have to distinguish two distinct worlds, the quantum world of microscopic entities and the classical world of our everyday experience which is subject to classical physics. In the quantum world we are confronted with many strange features, complementarity, nonindividuality, nonlocality, and the loss of deter-minism. However, the apparatuses which measure and register the properties of the quantum system as well as the human observer, who reads the observed data are parts of the classical world that is free from the quantum physical absurdities mentioned. For describing and interpreting quantum physics we can use common language and classical logic. We will query this doctrine here for several reasons. Firstly, during the last decades it became obvious that quantum mechanics is not restricted to the microscopic world of nuclei, atoms, and molecules but can be applied also to 1