Home / Topics / Particle Physics & Cosmology
Matter–antimatter asymmetry
Advanced
Why the universe contains more matter.
The universe contains almost no antimatter, with baryon-to-photon ratio ~10⁻⁹. Sakharov's conditions: baryon number violation, C and CP violation, and non-equilibrium.
For every billion antiquark-quark pairs one extra quark survived.
No complete explanation known.
In more detail
The universe contains far more matter than antimatter, and the reasons are still unknown. Explaining this asymmetry requires CP violation and other conditions discovered by Sakharov.
Real-world uses
- Physicists search for new sources of CP violation to explain the asymmetry.
- Cosmology constrains models of the early universe.
- Cosmologists explain why we live in a universe made of matter rather than antimatter using processes that include CP violation.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
Why does the asymmetry matter?
Without it, matter and antimatter would have annihilated, leaving little matter behind.
What are Sakharov's conditions?
Baryon number violation, C and CP violation, and departure from thermal equilibrium.
Why is the asymmetry a puzzle?
The Big Bang should have produced equal amounts of matter and antimatter, which would have annihilated, leaving almost nothing.
Related topics in Particle Physics & Cosmology
Particle detectors · Neutrino oscillations · CP violation · Grand unified theories · Supersymmetry · String theory