How Classical Particles Emerge From the Quantum World

Abstract

The symmetrization postulates of quantum mechanics (symmetry for bosons, antisymmetry for fermions) are usually taken to entail that \emph{quantum particles} of the same kind (e.g., electrons) are all in exactly the same state and therefore indistinguishable in the strongest possible sense. These symmetrization postulates possess a general validity that survives the classical limit, and the conclusion seems therefore unavoidable that even classical particles of the same kind must all be in the same state--in clear conflict with what we know about classical particles. In this article we analyze the origin of this paradox. We shall argue that in the classical limit classical particles \emph{emerge}, as new entities that do not correspond to the "particle indices" defined in quantum mechanics. Put differently, we show that the quantum mechanical symmetrization postulates do not pertain to \emph{particles}, as we know them from classical physics, but rather to indices that have a merely formal significance. This conclusion raises the question of whether the discussions about the status of identical quantum particles have not been misguided from the very start.

References in corpus (2)

• Discerning Elementary Particles
• Identical Quantum Particles and Weak Discernibility

Cited by in corpus (8)

• Discerning "indistinguishable" quantum systems
• Quantum Reality, Perspectivalism and Covariance
• Qualitative individuation in permutation-invariant quantum mechanics
• The Logic of Identity: Distinguishability and Indistinguishability in Classical and Quantum Physics
• Revisiting the Applicability of Metaphysical Identity in Quantum Mechanics
• Physical entanglement in permutation-invariant quantum mechanics
• Is There a Unique Physical Entropy? Micro versus Macro
• Contextuality and nonlocality of indistinguishable particles