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Individuality, Distinguishability, and Entanglement

After 3 years at the University of Bonn the project is now located at the University of Siegen.

Similar quantum objects, such as photons or electrons, are indistinguishable, merely permuting the particles doesn't change the state, and their individuality is questionable. Here lies the main difference to the ontology of classical objects that are individuals in a rather rich sense. Quantum particles violate Leibniz Principle of the Identity of Indiscernibles (received view) or differ only weakly (weak discernibility). Strucural realists have drawn the radical consequence that (fundamentally) there are only structures and no objects anymore. In any case, a revisionary ontology (e.g. process or trope ontologies) is required.The working hypothesis is that all this can only be said since permutation invariance is not properly distinguished from entanglement. Based on a recently purported physicists' distinction between purely permutation invariant states and physically meaningful entangled states, it will be investigated whether Leibniz' principle can still be established for quantum particles. Different types of states will require different defense strategies of Leibniz' principle, in particular a special one for (bosonic) symmetric product states. The main purpose is to show that quantum objects in fact are indiviuated by distinguishing properties. The second aim is to provide a new ontological distinction between fermions and bosons, i.e. to determine the ontological significance of Pauli exclusion. This throws new philosophical light on empirical facts such as Fermi pressure and Bose condensation.

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