Cosmic Microwave Background
Definition
The afterglow of the Big Bang — faint microwaves arriving from every direction, the oldest light in the universe.
Symbol: ·
Technical definition
Blackbody radiation at T = 2.725 K, released at recombination (~380,000 years after the Big Bang); its tiny anisotropies (~10⁻⁵) seeded cosmic structure.
Example
About 1% of the static on old analog TVs was the CMB — viewers were literally watching the Big Bang's afterglow between channels.
Common confusion
The CMB is not the Big Bang 'explosion' seen directly — it is light freed when the universe cooled enough for atoms to form, 380,000 years later.