The Quest for Cosmic Inflation

2014 is the 50th anniversary of the discovery of the Cosmic Microwave Background (CMB). Discovered accidentally in 1964 by two scientists from Bell Laboratories in New Jersey, Arno Penzias and Robert Wilson, who initially thought that the interference was caused by pigeon droppings on their antenna, CMB is a faint glow that permeates the entire universe, dating back to just 380,000 years after the Big Bang. Earlier, the baby universe was too hot and dense for light to travel far without interfering with matter 1 but when it cooled to the point that neutral atoms could form, light could travel through space unimpeded, giving rise to the CMB. Eventually, it was realized Penzias and Wilson had found an imprint from the primordial universe, a discovery that won them the 1978 Nobel Prize in Physics.

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.