On the Relationships between Classical and Quantum Mechanics

Abstract

Almost a century since the birth of quantum mechanics, in presence of an impressive and still developing accumulation of empirical evidence of quantum behaviour from the atomic scale down to the subnuclear scale and up to the astronomical one, much attention is still focused on the foundations of quantum theory. In particular there are still open problems about the relationship between classical and quantum features. For instance, why putting together quantum objects (like atoms) to get a compound system one progressively looses the quantum behaviour? Why we never encounter macroscopic objects in those nonlocalised states (think, e.g., of the states staying on both arms of an interferometry device) in which its atoms, when isolated, would be able to live? The difficulty to find convincing answers is behind the puzzling aspects of the quantum theory of measurement, and behind the so-called paradoxes of quantum theory. Interesting conjectures can be found in the literature: for instance the GRW model based on the assumption of a dynamical process of spontaneous localization, or the idea that for open systems the interaction with the environment might be responsible for the transition from quantum to classical.