| The main theme of this dissertation is the emergence of the "classical" world of our experience from quantum mechanics. The underlying key ingredient to be discussed is decoherence, i.e., the dislocalization of local phase relations through entanglement with environmental degrees of freedom. The analysis of a decoherence-based quantum-to-classical transition is approached from four different points of view.; First, key features of the decoherence program are clarified, and implications of decoherence for the quantum measurement problem and for the existing interpretations of quantum mechanics are extensively discussed.; Second, a critical analysis of the "self-induced decoherence" approach is presented. This approach has claimed to provide an alternative viewpoint on decoherence and to bypass some of the conceptual difficulties often associated with environmental decoherence. It is shown that this approach not only falls short of describing a physically relevant decoherence mechanism, but also fails in a large class of model systems.; Third, a derivation of the quantum-probability concept and the Born rule from symmetries in quantum entanglement is analyzed. In particular, important key assumptions not mentioned in the original exposition of the derivation are identified.; Fourth, recent experiments are discussed that have demonstrated the existence of superpositions of macroscopically distinct states. The crucial role of decoherence in these experiments is analyzed, and the implications for minimal non-collapse quantum mechanics and physical collapse models are investigated.; Based on these studies, it is concluded that pure quantum features, most notably, quantum entanglement and the resulting decoherence effects, are well capable of explaining the emergence of classicality in unitary quantum mechanics. |
