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Timeline of the Universe · event

Recombination

380,000 years · Radiation Era

Temperature (K)
3000
When
380,000 years
Redshift
z ≈ 1100
Era
Radiation Era
Seconds After Big Bang
11991633400000

What Happened

Electrons and protons combine into neutral hydrogen. The Saha equation puts this at 3000 K — far below hydrogen's 13.6 eV binding energy — because photons outnumber baryons a billion to one, and the rare energetic ones keep breaking atoms apart long past the naive temperature.

Researchers

Julien LesgourguesJames Peebles

Equations

Boltzmann DistributionSaha Ionization EquationRydberg FormulaBohr Model Energy Levels

Theories

Big Bang CosmologyBohr Model of the Atom

Referenced by

equation
Bohr Model Energy LevelsBoltzmann DistributionRydberg FormulaSaha Ionization Equation
researcher
James PeeblesJulien Lesgourgues
theory
Big Bang CosmologyBohr Model of the Atom

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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.