There is plenty of evidence that neutrinos have mass, so what could it reveal about the cosmic neutrino background (CNB) – the neutrino analogue of the cosmic microwave background (CMB)? With massless neutrinos, studies of the CNB would peer farther back in time (to about a second after the Big Bang) than researchers "see" with microwave photons (380,000 years after the Big Bang). Massive neutrinos go slower than the speed of light and, over timescales comparable to the age of the universe, that makes a big difference.

Scott Dodelson of Fermilab and Mika Vesterinen of the University of Manchester have shown that the CNB originates from a distance of 1–10 billion light-years – less than the 40 billion light-years for the origin of the CMB, taking into account the expansion of the universe. This implies that the neutrinos of the CNB come from regions where there is now interesting astronomical data and could, if measurable, provide valuable information about what seeded the formation of distant galaxies and clusters of galaxies.