104 research outputs found
Which FLRW comoving 3-manifold is preferred observationally and theoretically?
The lack of structure greater than 10 Gpc/h in Wilkinson Microwave Anisotropy
Probe (WMAP) observations of the cosmic microwave background (CMB) favours
compact Friedmann-Lemaitre-Robertson-Walker (FLRW) models of the Universe. The
present best candidates based on observations are the Poincare dodecahedral
space S^3/I^* and the 3-torus T^3. The residual gravity effect favours the
Poincare space, while a measure space argument where the density parameter is a
derived parameter favours flat spaces almost surely.Comment: 3 pages, Twelfth Marcel Grossmann Meeting on General Relativity, ed.
Thibault Damour, Robert T Jantzen, Remo Ruffini, Singapore: World Scientifi
A residual acceleration effect due to an inhomogeneity
The perturbed Friedmann-Lemaitre-Robertson-Walker models allow many different
possibilities for the 3-manifold of the comoving spatial section of the
Universe. It used to be thought that global properties of the spatial section,
including the topology of the space, have no feedback effect on dynamics.
However, an elementary, weak-limit calculation shows that in the presence of a
density perturbation, a gravitational feedback effect that is algebraically
similar to dark energy does exist. Moreover, the effect differs between
different 3-spaces. Among the well-proportioned spaces, the effect disappears
down to third order in several cases, and down to fifth order for the Poincare
dodecahedral space S^3/I^*. The Poincare space, that which also is preferred in
many observational analyses, is better-balanced than the other spaces.Comment: 6 pages, 1 figure, v1 submitted to Proceedings of the Invisible
Universe International Conference, held in Paris, France, June 29-July 3,
2009 - after it is published, it will be found at
http://proceedings.aip.org/proceedings
Observational Approaches to the Topology of the Universe
Many different and complementary strategies for translating the basic
principle of multiple topological imaging into observational analysis are now
available, both for three-dimensional and two-dimensional catalogues.Comment: very compact, (2 page) write-up of invited review for Marcel
Grossmann IX Meeting in Roma, 1st page classifies and cites different
observational strategies, 2nd page reference list includes many key 1999/2000
reference
Topological acceleration in relativistic cosmology
Heuristic approaches in cosmology bypass more difficult calculations that
would more strictly agree with the standard Einstein equation. These give us
the well-known Friedmann-Lemaitre-Robertson-Walker (FLRW) models, and, more
recently, the feedback effect of the global topology of spatial sections on the
acceleration of test particles. Forcing the FLRW heuristic model on
observations leads to dark energy, which, pending fully relativistic
calculations, is best interpreted as an artefact. Could topological
acceleration also be an artefact of using a heuristic approach? A multiply
connected exact solution of the Einstein equation shows that topological
acceleration is present in at least one fully relativistic case---it is not an
artefact of Newtonian-like thinking.Comment: 4 pages, 1 figure, Multiverse and Fundamental Cosmology Conference,
10-14 September, 2012, Szczecin, Polan
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