Overview
The Cosmic Microwave Background (CMB) is the faint afterglow of the Big Bang, a nearly uniform bath of microwave radiation permeating the entire universe. Discovered accidentally in 1964 by Arno Penzias and Robert Wilson, it provides a snapshot of the universe when it was only about 380,000 years old, a crucial epoch known as recombination. Tiny temperature fluctuations within the CMB, meticulously mapped by missions like COBE, WMAP, and Planck, are the seeds from which all large-scale structures—galaxies, clusters, and superclusters—eventually grew. Studying these anisotropies allows cosmologists to precisely measure fundamental parameters of the universe, such as its age, composition, and geometry, while also probing the physics of the very early cosmos and testing theories of inflation.