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Vol. 53, No. 6
December 1999
pp. 945-949
Topology of the Universe: Background and recent observational approaches
BOUDEWIJN F ROUKEMA
Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411 007, India
Email: boud@iucaa.ernet.in
Abstract. Is the Universe (a spatial section thereof) finite or infinite? Knowing the global geometry of a Friedmann-Lemaître (FL) universe requires knowing both its curvature and its topology. A flat or hyperbolic (`open') FL universe is not necessarily infinite in volume.
Multiply connected flat and hyperbolic models are, in general, as consistent with present observations on scales of 1-20 h-1Gpc as are the corresponding simply connected flat and hyperbolic models. The methods of detecting multiply connected models (MCM's) are presently in their pioneering phase of development and the optimal observationally realistic strategy is probably yet to be calculated. Constraints against MCM's on ~ 1-4 h-1Gpc scales have been claimed, but relate more to inconsistent assumptions on perturbation statistics rather than just to topology. Candidate 3-manifolds based on hypothesised multiply imaged objects are being offered for observational refutation.
The theoretical and observational sides of this rapidly developing subject have yet to make any serious contact, but the prospects of a significant detection in the coming decade may well propel the two together.
Keywords Observational cosmology; cosmic topology; topology; galaxy clusters; quasars; cosmic microwave background.
Pacs 98.80.Es; 04.20.Gz; 02.40.-k; 98.54.-h |