Theories · theory Big Bang Cosmology Accepted · 1927 StatusAcceptedYear1927 SummaryThe universe was hot and dense and has been expanding ever since. Lemaître derived it from Einstein's equations; the microwave background, the light-element abundances, and the redshifts all agree. TimelineReheatingNeutrino DecouplingElectron–Positron AnnihilationBig Bang NucleosynthesisMatter–Radiation EqualityRecombinationPhoton Decoupling — the CMBThe Dark AgesThe First GalaxiesReionizationDark Energy Takes OverPresent DayThe Local Group Is AloneHeat Death EquationsHubble's LawFirst Friedmann EquationSecond Friedmann EquationCosmological RedshiftCritical DensitySaha Ionization EquationCosmological Equation of StateLinear Perturbation GrowthCosmological Fluid EquationFLRW Metric ProponentGeorge GamowGeorges LemaîtreJames Peebles Referenced by equationCosmological Equation of StateCosmological Fluid EquationCosmological RedshiftCritical DensityFLRW MetricFirst Friedmann EquationHubble's LawLinear Perturbation GrowthSaha Ionization EquationSecond Friedmann Equation eventBig Bang NucleosynthesisDark Energy Takes OverElectron–Positron AnnihilationHeat DeathMatter–Radiation EqualityNeutrino DecouplingPhoton Decoupling — the CMBPresent DayRecombinationReheatingReionizationThe Dark AgesThe First GalaxiesThe Local Group Is Alone researcherGeorge GamowGeorges LemaîtreJames Peebles Open on the Theories shelf — the interactive card, the filters, and everything alongside it. From the Theories database in Notion, last edited 2026-08-15. This page is the row, rendered by the build; nothing on it is written by hand.