2 research outputs found
Determining the shape of the Universe using discrete sources
Suppose we have identified three clusters of galaxies as being topological
copies of the same object. How does this information constrain the possible
models for the shape of our Universe? It is shown here that, if the Universe
has flat spatial sections, these multiple images can be accommodated within any
of the six classes of compact orientable 3-dimensional flat space forms.
Moreover, the discovery of two more triples of multiple images in the
neighbourhood of the first one, would allow the determination of the topology
of the Universe, and in most cases the determination of its size.Comment: 11 pages, no figure
Constraints on the Detectability of Cosmic Topology from Observational Uncertainties
Recent observational results suggest that our universe is nearly flat and
well modelled within a CDM framework. The observed values of
and inevitably involve uncertainties. Motivated
by this, we make a systematic study of the necessary and sufficient conditions
for undetectability as well as detectability (in principle) of cosmic topology
(using pattern repetition) in presence of such uncertainties. We do this by
developing two complementary methods to determine detectability for nearly flat
universes. Using the first method we derive analytical conditions for
undetectability for infinite redshift, the accuracy of which is then confirmed
by the second method. Estimates based on WMAP data together with other
measurements of the density parameters are used to illustrate both methods,
which are shown to provide very similar results for high redshifts.Comment: 16 pages, 1 figure, LaTeX2