The Big Bang
Definition
The hot, dense early state from which the observable Universe has been expanding for about 13.8 billion years.
Scientific overview
The Big Bang is not an explosion in space but an expansion of space itself from an extremely hot, dense beginning. The framework explains the expansion of the Universe, the abundances of the light elements, and the cosmic microwave background — three independent lines of evidence that together make it the foundation of modern cosmology.
Historical development
Georges Lemaître proposed an expanding Universe from a 'primeval atom' in 1927–1931; the discovery of the cosmic microwave background in 1965 confirmed the hot early state and settled the debate with the rival Steady State model.
Evidence
- The observed expansion of the Universe
- The cosmic microwave background
- The primordial abundances of hydrogen, helium, and lithium
Open questions
- What set the initial conditions?
- What preceded the hot Big Bang, if anything?
Rests on
Predicts
Related discoveries & objects
Related scientists
Knowledge connections
- PredictsThe Cosmic Microwave Background
- PredictsBig Bang Nucleosynthesis
- Part of modelThe Lambda-CDM Model
- Depends onThe Big Bang
- Depends onGeneral Relativity
- Related toThe Cosmic Microwave Background
- Related toThe Expansion of the Universe
- Studied byGeorges Lemaître
- Required byBig Bang Nucleosynthesis
- Required byRecombination
- Related toEntropy & the Arrow of Time
- Related toThe Lambda-CDM Model
- Related toCyclic & Bouncing Cosmologies
- Required byPrimordial Black Hole
- Followed byCosmic Inflation
Sources & references
The primary and reference sources this topic draws on.
- NASANational Aeronautics and Space Administration
Mission data, planetary science, space telescopes, and public-domain imagery.
Most NASA-produced imagery is in the public domain; individual items are checked for usage terms before publication.
- Planck CollaborationESA Planck mission / Planck Collaboration
Cosmic microwave background maps and the cosmological parameters of the ΛCDM model.