Three Generations of Quarks are Needed To Avoid Anti-Matter

As we have already discussed, the reason we have particles without anti-particles is because of CP violation. CP-violation caused slightly more particles to be produced in the big bang then anti-particles. Then all the anti-particles annihilated with a particle leaving only the excess of particles we observe today.

However, it takes 3 generations of quarks to have CP violation. CP violation is encoded in the CKM Matrix, a 3 by 3 matrix. (N=3 for 3 generations of quarks). You need a overall phase in the CKM matrix to have cp-violation. If there were less then 3 generations of quarks, say 2, then the new 2 by 2 CKM matrix would have no overall phase and hence no CP-violation.

It was not too long ago when scientists had not suspected there were three generations of quarks. If there weren’t, we would have no CP-violation and no matter. It would have all been annihilated with the equal abundance of anti-matter.

By the way, in case you don’t know, the CKM matrix people won the Nobel Prize in physics last year.

CP Violation May Explain Why No Antimatter

CP symmetry says that every interaction in particle physics must obey charge conjugation and parity. (If you don’t understand the above statement don’t worry, you just need to know such a symmetry exists.)

Though CP symmetry was thought to be an exact symmetry, it turns out it is violated by  weak interactions.  If CP was an exact symmetry, there should be just as much antimatter produced by the big bang as matter.  However, as we look around us we should be easily convinced this isn’t the case. 🙂

However, since CP is violated, there should have been slightly more matter produced than antimatter.  Soon after the big bang every antimatter particle then annihilated itself with a matter particle leaving only the excess of matter which is seen today.  This is probably why there is no antimatter.