[Todos] Recordatorio IAFE-Coloquio: " IS THE UNIVERSE HOMOGENEOUS? "

[difusion en iafe.uba.ar]

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                    PRÓXIMO COLOQUIO DEL IAFE
                 Instituto de Astronomía y Física del Espacio
                           CONICET-UBA
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                   "IS THE UNIVERSE HOMOGENEOUS?"

                            Roy Maartens
           The University of the Western Cape, Cape Town ,South Africa
                   Miercoles 13 de abril 2011, 14:30hs.
                        Aula del Edificio IAFE

Abstract:
The standard model of cosmology is based on the existence of spatially
homogeneous surfaces as the background arena for structure formation. The
homogeneity assumption underpins both general relativistic and modified
gravity models. This assumption is central to the way in which we
interpret observations of the CMB and the galaxy distribution. It is
therefore crucial to probe the foundations of the homogeneity assumption.
Homogeneity cannot be directly observed in the galaxy distribution, even
with perfect observations, since we observe on the past lightcone and not
on spatial surfaces. But we can test consistency of the homogeneity
assumption. I will describe what we can do without the Copernican
Principle: at most, we can deduce isotropy of the Universe from isotropic
observations of matter on the past lightcone. Isotropy of the CMB tells us
very little without a Copernican assumption. With the Copernican
Principle, it is possible to deduce homogeneity of the Universe from
isotropy of matter observations - but it is not straightforward, contrary
to common belief. The most powerful result is based on the CMB: the
vanishing of the dipole, quadrupole and octupole of the CMB leads to
homogeneity. The observed CMB has small but nonzero multipoles, and I will
discuss what we can deduce from almost-isotropy of the CMB. Finally, I
discuss how we can use observations of galaxies and clusters to test the
Copernican Principle.