Illustration: Courtesy of Shankar Agarwal and Hume Feldman, University of Kansas; submitted to Mon. Not. R. Astron. Soc.

Figure 1: Comparison of density distribution in the Universe with (left) and without (right) massive neutrinos. The maps are based on numerical simulations [8]. The colors account for the density of ordinary (baryonic) matter in one slice of the simulation box [9]. The two simulations started from the same initial conditions, with either $Mν=0$ (right) or $Mν=1.9eV$ (left). In the massive neutrino case, matter is spread over a larger number of structures and there is less density contrast. (The unrealistically large neutrino mass of $1.9eV$ was chosen so as to make the comparison clear.)