Gauge Is More Than Mathematical Redundancy

Abstract

Physical systems may couple to other systems through variables that are not gauge invariant. When we split a gauge system into two subsystems, the gauge-invariant variables of the two subsystems have less information than the gauge invariant variables of the original system; the missing information regards degrees of freedom that express relations between the subsystems. All this shows that gauge invariance is a formalization of the relational nature of physical degrees of freedom. The recent developments on boundary variables and boundary charges are clarified by this observation.

arXiv comment3 pages. To appear in the proceedings of the conference "One Hundred Years of Gauge Theory, Bad Honnef 2018", S. De Bianchi and C. Kiefer eds

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• Gravitational $SL(2,\mathbb{R})$ Algebra on the Light Cone
• On the Meaning of Local Symmetries: Epistemic-Ontological Dialectics
• Soft edges: the many links between soft and edge modes
• Impact of generalized holonomy corrections on the cosmological primordial power spectra
• Corners of gravity: the case of gravity as a constrained BF theory
• Barnich-Troessaert Bracket as a Dirac Bracket on the Covariant Phase Space