Max Planck Institute for Dynamics and Self-Organization -- Department for Nonlinear Dynamics and Network Dynamics Group
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MPI Kolloquium

Wednesday, 13.07.2011 16 c.t.

Gravity as Machian shape dynamics

by Dr. Julian Barbour
from Visiting Professor in Physics at the University of Oxford

Contact person: Armin Biess


Ludwig Prandtl Hörsaal, Am Faßberg 11 AI-Gebäude


Shape Dynamics, described in arXiv: 1105.0183, is an alternative theory of gravity inspired by Mach's penetrating critique of Newton's concepts of absolute space and time. Mach's ideas were the primary stimulus to Einstein's creation of general relativity, but he attempted to implement them indirectly. Shape Dynamics is a direct implementation and requires that time, position, and size should all be relative. Relativity of size, realized through three-dimensional conformal invariance, is a symmetry requirement that Einstein did not invoke, but leads rather remarkably to a classical theory that agrees with Einstein's general relativity in the so-called constant-mean(extrinsic)-curvature (CMC) foliation and provides a first-principles dynamical derivation of York's invaluable method for solving the initial-value problem of general relativity. There are indications that, through its different symmetry principle and introduction of a distinguished notion of simultaneity, Shape Dynamics may be better suited to quantization than general relativity. I shall concentrate on the conceptual aspects, which relate to the centuries-old debate about the nature of time, space and motion, and keep the technical details to the essential minimum.

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