Distinguishable-and Indistinguishable-particle Descriptions of Systems of Identical Particles

The problem of distinguishability of identical particles is considered from both experimental and theoretical points ofview. It is argued that distinguishability has to be defined relative to a definite set of experiments and that the criterion by which the particies are distinguished should be specified. Faiiure to do so may cause mismatching between theory and experiment. On the theoretical level a distinction is made between indexedand unindexed-particle theories, indices being unobserved intrinsic properties of the particles. A fieid theory of indexed particies is constructed and shown to be equivalent to the second quantization formalism, which is an unindexed-particle theory.