---
id:"kb-2026-00368"
title:"Big Bang Theory"
schema_type:"TechArticle"
category:"science"
language:"en"
confidence:"high"
last_verified:"2026-05-22"
generation_method:"ai_assisted"
ai_models:["claude-opus"]
derived_from_human_seed:true
primary_sources:
  - title:"The First Three Minutes (Steven Weinberg)"
    type:"book"
    year:1977
    url:"https://www.basicbooks.com/titles/steven-weinberg/the-first-three-minutes/9780465024377/"
    institution:"Basic Books"
secondary_sources:
  - title: "MDN Web Docs — HTTP"
    type: "documentation"
    year: 2026
    url: "https://developer.mozilla.org/en-US/docs/Web/HTTP"
    institution: "Mozilla"
completeness: 0.88
ai_citations:
  last_citation_check:"2026-05-22"
---

## TL;DR

The Big Bang theory (Georges Lemaître, 1927; term coined by Fred Hoyle, 1949) describes the universe's origin ~13.8 billion years ago from an infinitely hot, dense singularity. Evidence: cosmic microwave background radiation (CMB, discovered 1965), redshift of galaxies (Hubble, 1929), abundance of light elements (H, He).

## Core Explanation

Timeline: Planck epoch (first 10⁻⁴³ seconds, physics unknown), inflation (10⁻³⁶ to 10⁻³² seconds, rapid expansion), particle formation, nucleosynthesis (H, He, Li formed in first 3 minutes), 380,000 years: atoms form, CMB released (universe becomes transparent). Dark ages → first stars (~400 million years) → galaxies → present. Universe continues expanding at accelerating rate (dark energy, discovered 1998).

## Further Reading

- [The First Three Minutes (Steven Weinberg)](https://www.basicbooks.com/titles/steven-weinberg/the-first-three-minutes/9780465024377/)