Cosmic microwave background
The cosmic microwave background (CMB) is the near-uniform relic radiation from the hot early universe, now observed as a 2.7 K blackbody glow permeating all directions. Tiny temperature and polarization anisotropies in the CMB encode precise information about the universe’s contents, geometry, and early physics, measured most notably by the COBE, WMAP, and Planck space missions.
