Phase transitions as a manifestation of spontaneous unitarity violation

Abstract

Spontaneous symmetry breaking is well understood under equilibrium conditions as a consequence of the singularity of the thermodynamic limit. How a single global orientation of the order parameter dynamically emerges from an initially symmetric state during a phase transition, however, is not captured by this paradigm. Here, we present a series of symmetry arguments suggesting that singling out a global choice for the ordered state is in fact forbidden under unitary time evolution, even in the presence of an environment and infinitesimal symmetry breaking perturbrations. We thus argue that the observation of phase transitions in our everyday world presents a manifestation of the unitarity of quantum dynamics itself being spontaneously broken. We argue that this agrees with the observation that Schrödinger's time dependent equation is rendered unstable for macroscopic objects owing to the same singular thermodynamic limit that affects equilibrium configurations.

To appear in a special issue celebrating the 80th birthday of Sir Michael Berry

References in corpus (1)

• Coherence lifetimes of excitations in an atomic condensate due to the thin spectrum

Cited by in corpus (4)

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• Colored noise driven unitarity violation causing dynamical quantum state reduction
• Continuous spontaneous localization as the white-noise limit of spontaneous unitarity violation
• New insights on the quantum-classical division in light of Collapse Models