It is hard to imagine that this seemingly innocuous discovery would one day become the pillar of modern observational astronomy. This article describes the journey that began fifty years ago with the discovery of CMB by Penzias and Wilson until now, when a group of scientists in the USA, by studying fluctuations in swirls of polarized light in the CMB, unearthed possible evidence that the Big Bang 2, 3 had indeed happened 13.82 billion years ago. In order to follow the progression of ideas in these fifty years, one must start at the very beginning, the Big Bang.
1 Neutral hydrogen formed about 380,000 years after the Big Bang. Prior to this time, the constant interaction between matter (electrons) and light (photons) made the universe opaque.
2 Specifically, the researchers of the Background Imaging of Cosmic Extragalactic Polarization 2 (BICEP2) experiment found evidence of inflation that caused the early universe to expand exponentially for a very short period of time. Inflation cosmology, or simply inflation, is the subject of Section 6.
3 BICEP2’s results were recently challenged by other groups. See here for details.