Julian Barbour: Shape Dynamics - Principles and Possibilities

Recording from the Online Workshop “Shape Dynamics - Achievements and Perspectives in Relational Physics“. Sept. 30 - Oct. 1, 2021. Julian Barbour Shape Dynamics: Principles and Possibilities Abstract: Shape dynamics aims to recast and unify the foundations of physics and cosmology. It is a relational formulation of dynamically closed classical universes and a conjectured basis for their quantum description. The fundamental entities are shapes defined by points and angles. Only ratios of quantities of the same kind, pure numbers, appear. The principles and possibilities that flow from them are illustrated in a Newtonian model of point particles in Euclidean space; the generalisation to Riemannian geometries and multiple forces is sketched. The set of all shapes is shape space. It is compact and a natural metric on it defines a probability measure. The primary invariant of the theory’s fundamental symmetry group is called the complexity. It is a continuous function on shape space, bounde