Comparative Theory of Background Independence

Abstract

The Lie claw digraph has recently been shown to control Background Independence and thus both the Problem of Time and the nature of Physical Law. This is established for Flat and Differential Geometry with varying amounts of extra mathematical structure. This Lie claw digraph has Generator Closure at its centre, Relationalism at its root, and Assignment of Observables and Constructability from Less Structure Assumed (working if Deformation leads to Rigidity) on its other leaves. The centre is enabled by automorphisms and powered by the Lie Algorithm generalization of the Dirac Algorithm (itself holding for the canonical subcase, with constraints for generators). We now explain how such claws are universal over all levels of mathematical structure that could be considered to be Background Independent. This follows from automorphisms both being categorical and supplying the centre with enough machinery to control the 3 peripheral aspects. Such claws in general thus merit a new name: UBIC (Universal Background Independence Claws) including allusion to their ubiquity. For a given level, the Problem of Time facets are ordered into two UBIC: the spacetime primality copy and the space/dynamics/canonical primality copy. These may or may not have a Wheelerian 2-way route connecting them: Constructability of Spacetime from Space and Intermediary Object Independence. The 3 cases of Constructability furthermore take one up and down levels like the ramps in a multi-storey car park. Wheeler matrices and ramp matrices (or more generally digraphs) codify this information. These summarize the main features of each Background Independent Theory that can vary between levels, the Constructabilities and Intermediary Object Independence being selection principles rather than categorical. These selection principles indicate that Background Independence has reached maturity as a field of study.