München 2019 – wissenschaftliches Programm

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SYKM: Symposium Kosmologische Modellbildung

SYKM 1: Cosmological Model-Building

SYKM 1.1: Hauptvortrag

Dienstag, 19. März 2019, 16:30–17:10, HS 4

Conceptual problems with cosmological model-building from the point of view of General Relativity — •George Ellis — University of Cape Town

General Relativity is a highly non-linear theory without a fixed background space-time. This means that apparently physical properties can be nothing but coordinate effects. One should therefore as far as possible use invariant quantities in covariant equations, and calculate non-local effects in terms of potentially observable quantities (as for example in the case of black hole properties).

Cosmology separates into Kinematics (relations independent of the gravitational field equations), dynamics (relations dependent on those equations), and model confirmation/ testing. These issues arise firstly as regards the background model, giving the overall dynamics of the universe, and then as regards perturbed models where structure formation can be investigated. In the latter case a variety of important issues arise: the gauge issue for perturbations, and the averaging, backreaction, and fitting problems relating the perturbed and background models. Testing models is strongly restricted both by visual horizons, and by limits on testing the relevant physics. The strongest limits on background model parameters come from observations of astronomical structures and associated Cosmic Background Radiation anisotropies, because the background model provides the context for structure growth.