Ethan Siegel in Forbes:
The Big Bang, when it was first proposed, seemed like an outlandish story out of a child’s imagination. Sure, the expansion of the Universe, observed by Edwin Hubble, meant that the more distant a galaxy was, the faster it receded from us. As we headed into the future, the great distances between objects would continue to increase. It’s no great extrapolation, then, to imagine that going back in time would lead to a Universe that was not only denser, but thanks to the physics of radiation in an expanding Universe, hotter, too. The discovery of the cosmic microwave background and the cosmic light-element background, both predicted by the Big Bang, led to its confirmation. But last year, a leftover glow unlike any other — of neutrinos — was finally seen. The final, elusive prediction of the Big Bang has finally been confirmed. Here’s how it all unfolded.