Astronomy and Astrophysics – Astrophysics
Scientific paper
1999-04-16
Nature 401 (1999) 252
Astronomy and Astrophysics
Astrophysics
8 pages, 1 figure. Slightly revised version. Letter to Nature
Scientific paper
10.1038/45748
Recent observations of high-redshift supernovae seem to suggest that the global geometry of the Universe may be affected by a `cosmological constant', which acts to accelerate the expansion rate with time. But these data by themselves still permit an open universe of low mass density and no cosmological constant. Here we derive an independent constraint on the lower bound to the mass density, based on deviations of galaxy velocities from a smooth universal expansion. This constraint rules out a low-density open universe with a vanishing cosmological constant, and together the two favour a nearly flat universe in which the contributions from mass density and the cosmological constant are comparable. This type of universe, however, seems to require a degree of fine tuning of the initial conditions that is in apparent conflict with `common wisdom'.
Dekel Avishai
Zehavi Idit
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