Big Bang Nucleosynthesis

10 s – 20 minutes · Radiation Era

Temperature (K): 1000000000
When: 10 s – 20 minutes
Redshift: —
Era: Radiation Era
Seconds After Big Bang: 180

What Happened

Protons and neutrons fuse into deuterium, helium-4 and a trace of lithium-7, then stop as the universe cools below the fusion threshold. It freezes in about 24% helium by mass — a prediction that matches observation to two decimal places, and one of the three pillars.

Researchers

George Gamow Ralph Alpher James Peebles

Equations

Radioactive Decay Law Boltzmann Distribution First Friedmann Equation Saha Ionization Equation

Theories

Big Bang Nucleosynthesis Big Bang Cosmology

Referenced by

equation

Boltzmann Distribution First Friedmann Equation Radioactive Decay Law Saha Ionization Equation

researcher

George Gamow James Peebles Ralph Alpher

theory

Big Bang Cosmology Big Bang Nucleosynthesis

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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.