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.
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Notes
- 1.
I thank Laurent Freidel for pointing out this example.
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Rovelli, C. (2020). Gauge Is More Than Mathematical Redundancy. In: De Bianchi, S., Kiefer, C. (eds) One Hundred Years of Gauge Theory. Fundamental Theories of Physics, vol 199. Springer, Cham. https://doi.org/10.1007/978-3-030-51197-5_4
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