Speaker
Description
One of the most basic notions in physics is the partitioning of a system into subsystems, and the study of correlations among its parts. Operationally, subsystems are distinguished by physically accessible observables which are often implicitly specified relative to some external frame, such as the laboratory, or a background notion of locality. In absence of external relata (as in Page-Wootters dynamics, gauge theories, and gravity), physical observables must be relationally specified relative to some internal dynamical degrees of freedom. Moving from simple finite-dimensional systems to local subregions in gauge theories, where the dynamical frames are provided by boundary edge modes, in this talk, I discuss how different internal frames identify distinct external-frame-independent/gauge-invariant algebras of subsystem’s observables. As a result, physical properties of subsystems are contingent on the choice of the internal frame. Special attention is reserved to subsystem entropies; in particular, I explain how such a relational definition of subsystems provides an alternative proposal for defining a gauge-invariant notion of entanglement entropy.