“These neutrino observations are so exciting and significant that I think we’re about to see the birth of an entirely new branch of astronomy: neutrino astronomy.” -John Bahcall
From the Hubble expansion of the Universe to isotropy and homogeneity to the light elements to the leftover radiation glow to the formation of large-scale structure in the Universe, the Big Bang is by far the most successful scientific description of the Universe of all-time.
Even with the add-ons of dark matter, dark energy and inflation, the Big Bang still thrives, accounting for all of those phenomena and leading to observable predictions that have since been verified. But there’s one thing it’s predicted that we haven’t been able to test: a cosmic background of low-energy, relic neutrinos. We know they need to be there if the Big Bang is correct, but we don’t know how to successfully detect them.