Quantum Haecceity

TL;DR

This paper explores the concept of identity in quantum systems, arguing that a weaker form of 'haecceity' called 'quantum haecceity' is necessary to understand symmetrization, challenging traditional assumptions about quantum indistinguishability.

Contribution

It introduces the concept of 'quantum haecceity' and questions the necessity of symmetrization postulates, linking symmetrization to physical conditions rather than permutation invariance.

Findings

Strong haecceity does not apply at the quantum level

Symmetrization arises from physical conditions, not permutation invariance

Perturbative Hamiltonian is needed for exchange effects

Abstract

There is an extensive philosophical literature on the interrelated issues of identity, individuality, and distinguishability in quantum systems. A key consideration is whether quantum systems are subject to a strong form of individuality termed "haecceity" (from the Latin for "this-ness"). I argue that the traditional, strong form of haecceity does not apply at the quantum level, but that in order to properly account for the need for symmetrization in quantum systems, a weaker kind of haecceity must be involved, which I call "quantum haecceity." In the process, I also question some generally accepted tenets of the current debate, such as the idea that symmetrization of states for identical quanta must be postulated and reflects permutation invariance. Instead, I note that a perturbative Hamiltonian is required for exchange effects, which suggests that the need for symmetrization arises from specific physical conditions.