The Big Bang's final and most difficult prediction: confirmed

"The idea of the Big Bang has captivated the imagination of humanity since it was first proposed nearly a full 100 years ago. Since the Universe is expanding today (as observations have indicated since the 1920s), then we can extrapolate back, earlier and earlier, to when it was smaller, younger, denser, and hotter. You could go back as far as you can imagine: before humans, before the stars, before there were even neutral atoms."

"As time went forward, the Universe would cool, expand, and gravitate all together. First atomic nuclei would form from protons and neutrons, then neutral atoms would form, and then gravitation would lead to stars, galaxies, and the grand structures of the cosmic web. These leftover relics - the light elements formed in the Big Bang, the relic photons from the primordial plasma,"

"But remaining from an even earlier epoch, a fifth cornerstone should exist as well. There would be an early signal left over from when the Universe was just one second old: a bath of neutrinos and antineutrinos. Known as the cosmic neutrino background (CNB), it was theorized generations ago but was dismissed throughout the 20th century as being fundamentally undetectable."

"That's no longer the case. Two very clever teams of scientists, using cutting-edge data from both cosmic microwave background data and from large-scale structure data, each found a way to detect it. The data is in, and the results are incontrovertible: the cosmic neutrino background is real, and its observed properties agree with the predictions of the Big Bang. Here's the story of how the Big Bang's fifth and final great prediction was confirmed."

The Universe's expansion permits extrapolation to earlier times when it was smaller, hotter, and denser. At the earliest moments, all particle and antiparticle species, including presently inaccessible fundamental particles, would have been produced. As it cooled and expanded, protons and neutrons combined into nuclei, neutral atoms formed, and gravity assembled stars, galaxies, and the cosmic web. The primordial light elements, relic photons, large-scale structure, and cosmic expansion constitute four classical evidences of the Big Bang. A fifth relic—an early bath of neutrinos and antineutrinos from when the Universe was about one second old—has now been detected through combined cosmic microwave background and large-scale structure analyses, with observed properties matching Big Bang predictions.

Read at Big Think