Topic summary
CP symmetry
Extracted from the Wikipedia article CP violation.
Matter–antimatter imbalance
The Big Bang should have produced equal amounts of matter and antimatter if CP symmetry was preserved; as such, there should have been total cancellation of both—protons should have cancelled with antiprotons, electrons with positrons, neutrons with antineutrons, and so on. This should have resulted in a sea of radiation in the universe with no real matter, only virtual matter that fluctuates and propagates the radiation. Since this is not the case, after the Big Bang, physical laws must have acted differently for matter and antimatter; i.e. violating CP symmetry.