2 Angular power spectrum
The evidence that space might have an unusual shape is obvious when we plot the level of temperature fluctuations in the cosmic microwave background as a function of angle, θ (top). The WMAP data are shown in green (purple depicts earlier data) and the modes of the spectrum are defined as L = 180°/θ. The largest angular scales (or lowest modes) are very sensitive to the global shape or topology of space. In this region (bottom), data from WMAP do not agree with theoretical predictions for an infinite Euclidean space (red curve), whereas predictions based on a Poincaré dodecahedral space (blue curve) do agree. This suggests that we live in a multiply connected spherical space.