The cosmic microwave background (CMB) is the oldest light in the universe, a faint glow left over from the Big Bang. This article explores its origin, the cosmic epochs it reveals, and how it shapes our understanding of the universe’s evolution.
The last scattering surface is the sphere of light emitted about 380,000 years after the Big Bang, when the universe cooled enough for electrons and protons to form neutral hydrogen. This cosmic relic, observed as the cosmic microwave background, provides a snapshot of the infant universe and anchors our understanding of cosmic evolution from the Planck epoch to the present day.
