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THE QUESTION LIBRARY THE UNIVERSE
Why do physicists still call the matter-antimatter imbalance unsolved?
Why the matter surplus remains unexplained, what Sakharov's conditions require, and how sphalerons and proposed neutrino mechanisms might connect.
THE SHORT ANSWER
Known physics supplies important ingredients, but no confirmed mechanism accounts for the observed matter surplus. A successful explanation must generate the right amount, preserve it as the universe cools, and agree with other measurements. Sakharov's conditions describe the conventional recipe. Sphaleron processes and proposed neutrino mechanisms show how pieces could connect; a plausible calculation is not proof of the universe's history.
- A measured asymmetry is not a complete cosmic history.
- Sakharov's conventional conditions need a quantitative mechanism.
- Leptogenesis proposes new neutrino ingredients rather than confirming their discovery.
WHAT WE DON’T KNOW YET
Which mechanism generated the cosmic surplus, and which proposed additional states actually exist, remain unknown.
WHAT WOULD CHANGE THIS ANSWER
Independent evidence for a proposed mechanism's new ingredients, a consistent abundance calculation and successful further observational tests.
Known physics supplies important ingredients, but no confirmed mechanism accounts for the observed matter surplus. A successful explanation must generate the right amount, preserve it as the universe cools, and agree with other measurements. Sakharov's conditions describe the conventional recipe. Sphaleron processes and proposed neutrino mechanisms show how pieces could connect; a plausible calculation is not proof of the universe's history.
THE LONG ANSWER
THE LONG ANSWER · ABOUT 2 MINUTES
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God Plays Dice answers big questions in plain words, with sources and one of six honest labels.
Words worth knowing (3)
- baryogenesis
- The generation of an imbalance between baryons and antibaryons.
- leptogenesis
- A proposed generation of a lepton imbalance that helps produce a baryon imbalance.
- thermal equilibrium
- A condition in which opposing thermal processes balance statistically.
Sources & further reading
(4) · Checked Oct 5, 2026
- Searching for matter–antimatter asymmetry with the Higgs boson ↗CERNOfficial explanation: known measured asymmetry sources do not account for the surplus; no universal exclusion of all extended histories.
- Violation of CP invariance, C asymmetry, and baryon asymmetry of the universe ↗A. D. Sakharov; Soviet Physics Uspekhi1967 original paper reprinted 1991; conditions used without adopting its historical speculative particle model.
- The Sphaleron Rate in the Minimal Standard Model ↗D'Onofrio, Rummukainen and Tranberg; Physical Review Letters2014 original lattice calculation; baryon/lepton changes, conversion role and smooth crossover under model assumptions.
- Baryogenesis without grand unification ↗Fukugita and Yanagida; Physics Letters BOriginal proposed mechanism adds right-handed Majorana neutrinos and transfers a lepton surplus; not an observed cosmological history.
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CONTINUE THE THREAD
Where this question leads.
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