Cosmic Microwave Background (CMB)
The electromagnetic thermal radiation leftover from the recombination epoch of the early universe (~380,000 years after the Big Bang).
Governing formula
T_CMB = 2.72548 ± 0.00057 K, λ_peak ≈ 1.06 mm
SI unit
Kelvin (2.725 K Blackbody)
In depth
Discovered by Penzias and Wilson in 1964 (Nobel Prize 1978). Represents the oldest light in the universe. Temperature fluctuations (ΔT/T ~ 10⁻⁵) mapped by COBE, WMAP, and Planck space telescopes reveal primordial seeds of cosmic structure.
Examples in the real world
Planck satellite temperature anisotropy maps confirming a flat universe composed of 68% dark energy, 27% dark matter, and 5% baryonic matter.