Photon Decoupling — the CMB

380,000 years · Radiation Era

Temperature (K): 2970
When: 380,000 years
Redshift: z ≈ 1100
Era: Radiation Era
Seconds After Big Bang: 11991633400001

What Happened

With the free electrons gone the universe turns transparent and the photons fly free. They are still arriving, stretched by a factor of 1100 into microwaves at 2.725 K: the oldest light there is, and the most perfect black body ever measured.

Researchers

George Gamow Robert Wilson Ralph Alpher Arno Penzias Julien Lesgourgues James Peebles George Smoot

Equations

Cosmological Redshift Planck's Law Wien's Displacement Law Kirchhoff's Law of Thermal Radiation

Theories

Steady State Theory Big Bang Cosmology

Referenced by

equation

Cosmological Redshift Kirchhoff's Law of Thermal Radiation Planck's Law Wien's Displacement Law

researcher

Arno Penzias George Gamow George Smoot James Peebles Julien Lesgourgues Ralph Alpher Robert Wilson

theory

Big Bang Cosmology Steady State Theory

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From the Cosmic Timeline database in Notion, last edited 2026-08-16. This page is the row, rendered by the build; nothing on it is written by hand.