Cosmic Microwave Background Radiation

Cosmic Microwave Background Radiation (CMB) is relic Electromagnetic Radiation from the early universe.

It was released when the universe cooled enough for atoms to form and photons could travel freely (roughly 380,000 years after The Big Bang).

Because of expansion of the universe, that ancient light has been stretched into the microwave range.

Why it matters

The CMB is one of the strongest observational pillars behind modern cosmology.

See also

• The Big Bang
• expansion of the universe
• Electromagnetic Radiation