Model provides clearest evidence yet of cosmic neutrino background

Ars Technica : The cosmic microwave background (CMB) was first discovered in the 1950s and gave evidence to the theory that the universe was created from a “big bang.” It is an echo of the early radiation formed from the explosion. Now a new analysis of the CMB hints at another leftover artifact: the cosmic neutrino background. As neutrinos passed through the early universe, they caused sonic shock waves, which changed the density and distribution of the other particles. In turn, that led to the formation of galaxies and hot and cold regions in the CMB. Simulations of the CMB with and without the sonic-boom effect, and with different numbers of neutrino types, found that the model that included the three known types of neutrinos was the best match with the actual CMB data.