14 March 2008
The 5-year WMAP papers tighten the bounds on the curvature of the universe, favoring an approximately flat space and excluding the Poincaré dodecahedral space as a viable explanation for the weak large-scale CMB fluctuations.
In terms of the total mass-energy density Ωtotal, the dodecahedal model would explain the weak large-scale CMB fluctuations when 1.015 < Ωtotal < 1.025. A flat universe corresponds to Ωtotal = 1. The latest observations find 0.9929 < Ωtotal < 1.0181 at the 95% confidence level.
7 March 2007
Back in 2003 the first-year data from the Wilkinson Microwave Anisotropy Probe (WMAP) found the cosmic temperature fluctuations on the largest scales (subtending angles of 60° or more across the sky) to be much weaker than one would expect in an infinite universe, but to match well what one would expect in a finite universe. Since then the mystery has only deepened.
The first-year WMAP data found the fluctuations to be unusually weak at the 1-in-600 level, meaning there’s roughly a 1-in-600 chance that they could be so weak in an infinite flat universe. The more recent three-year WMAP data find the fluctuations to be even weaker still. If one masks out the part of the sky contaminated by the Milky Way galaxy, one finds the fluctuations on the rest of the sky to be weak at roughly the 1-in-3000 level.
On the other hand, all efforts to find direct evidence for a finite universe have so far failed, so it’s not at all clear whether the weak fluctuations are due to a finite universe or some other cause.