12.9 The Asymmetry of Matter and Anti-Matter in the Universe
Many observations show that there is the asymmetry between matter and anti-matter. This is the most remarkable feature of our universe. A number of hypothesis are existed which show that the universe consists almost entirely of matter rather than anti-matter. e.g., the universe is assumed to be composed of of ordinary matter (electrons, protons and neutrons), of hydrogen atoms and of helium atoms, there are no any contribution of anti-hydrogen or anti-helium atoms in the composition of the universe.
The experimental results explain that the matter and anti-matter asymmetry is indeed due to the violation of conservation of baryon number. i.e., there is imbalance number of baryons and its anti-baryons. Now if the particle-antiparticle symmetry is also violated, then there will be a mechanism for making more quarks than anti-quarks, more leptons than anti-leptons and eventually more matter than anti-matter. Hence, it is concluded that the problem asymmetry of matter and anti-matter is still mystery.