The Cosmic Microwave Background (CMB) was accidentally discovered in 1964 by Arno Penzias and Robert Wilson.

While working at Bell Labs, Penzias and Wilson were testing a new horn antenna designed for satellite communication. They detected a persistent, annoying static, a faint hiss that seemed to come from every direction in the sky, independent of Earth's rotation or galactic position. Initially attributing it to equipment malfunction or even pigeon droppings, they meticulously removed all potential terrestrial interference. Unbeknownst to them, a team at Princeton University, led by Robert Dicke, had theoretically predicted the existence of such radiation as a leftover relic from the Big Bang. When the two teams connected, the accidental discovery was confirmed, providing the first robust observational evidence for the Big Bang theory. Penzias and Wilson were awarded the Nobel Prize in Physics in 1978 for their discovery. This serendipitous finding marked a turning point in cosmology, shifting the debate definitively towards the Big Bang model over the competing Steady State theory. The CMB's uniform nature and blackbody spectrum, later confirmed with extreme precision by COBE, WMAP, and Planck missions, perfectly matched theoretical predictions for an expanding, cooling universe that originated from a hot, dense state.