4 research outputs found
Light propagation in statistically homogeneous and isotropic dust universes
We derive the redshift and the angular diameter distance in rotationless dust
universes which are statistically homogeneous and isotropic, but have otherwise
arbitrary geometry. The calculation from first principles shows that the
Dyer-Roeder approximation does not correctly describe the effect of clumping.
Instead, the redshift and the distance are determined by the average expansion
rate, the matter density today and the null geodesic shear. In particular, the
position of the CMB peaks is consistent with significant spatial curvature
provided the expansion history is sufficiently close to the spatially flat
LambdaCDM model.Comment: 33 pages. v2: Published version. Corrected typo
The Standard Cosmological Model
The Standard Model of Particle Physics (SMPP) is an enormously successful
description of high energy physics, driving ever more precise measurements to
find "physics beyond the standard model", as well as providing motivation for
developing more fundamental ideas that might explain the values of its
parameters. Simultaneously, a description of the entire 3-dimensional structure
of the present-day Universe is being built up painstakingly. Most of the
structure is stochastic in nature, being merely the result of the particular
realisation of the "initial conditions" within our observable Universe patch.
However, governing this structure is the Standard Model of Cosmology (SMC),
which appears to require only about a dozen parameters. Cosmologists are now
determining the values of these quantities with increasing precision in order
to search for "physics beyond the standard model", as well as trying to develop
an understanding of the more fundamental ideas which might explain the values
of its parameters. Although it is natural to see analogies between the two
Standard Models, some intrinsic differences also exist, which are discussed
here. Nevertheless, a truly fundamental theory will have to explain both the
SMPP and SMC, and this must include an appreciation of which elements are
deterministic and which are accidental. Considering different levels of
stochasticity within cosmology may make it easier to accept that physical
parameters in general might have a non-deterministic aspect.Comment: 16 pages, 2 figures, invited talk at "Theory Canada 1", June 2005,
Vancouve