When my friend asked me about CP violation, I told them about some elementary particles physics. But it seemed they do not have background about this. So is there any daily practical activity that can explain CP violation? Thanks.
Our very existence is based on CP violation, but it's not fully understood yet. The point is that if nature would obey CP symmetry, then according to our present understanding of cosmology most likely the universe should have net-baryon number 0, i.e., an equal amount of matter and antimatter. Now this would imply that there's no baryonic matter at all, because every baryon ever produced in the hot and dense early stages of the universe would have annihilated mutually. Without baryonic matter, no nuclei necessary to build life as we know it would have been formed, and thus we'd not exist.
In the Standard Model of elementary particle physics, which is the most successful model about all known and so far observed particles, the CP symmetry (i.e., symmetry under C=exchange each particle by its antiparticle; P=space reflection) is violated. This was experimentally seen in 1964 for the first time on the system of neutral kaons:
and was a milestone in the understanding of the zoo of hitherto known particles. However, the CP violation in the standard model is very weak (after all it's only the weak interaction that breaks CP symmetry) to explain the amount of baryonic matter in the universe. So for a full understanding, why we exist, we have to work harder in particle physics and cosmology.
vanhees71 provided example of C-violation. But it's not CP-violation yet. It would still be possible to have a universe with more matter than antimatter, but P-symmetric.
An example of P-violation in daily life is the preference of dextro-sugars and levo-aminoacids in living organisms. It is not known if the biological P-violation stems from the physical P-violation. It might, but it is not proven. For example, the stereoisomers might have slightly different radioactivity or decay time and this difference built up over billions of years, so eventually the usual-handed molecules were chosen by evolution for building blocks of live.
Again, it is theoretically possible to have the C-symmetry and P-symmetry broken individually, but the CP-symmetry still intact. This would be the case if we had matter and equal amount of opposite-handed antimatter. This is not the case.
Thanks to the CPT-symmetry, breaking the CP-symmetry automatically breaks the T-symmetry. Should the CPT-symmetry be gone, we could have CP-symmetry broken but T-symmetry intact. But the CPT-symmetry holds within experimental error so the T-symmetry is broken too.
The problem with T-symmetry breaking is that it is very slight. So we don't see much of its influence in daily life. However we can imagine what would happen if the T-symmetry was broken strongly. First we have to know what the T-symmetry is. It is basically the symmetry between particle creation and annihilation. When you collide some particles and get some reaction results, then you could collide the results as well and get the original particles, and - speaking very informally - both processes should have the same probability. The T-symmetry is broken, and that means it is not the case. God tosses biased coin when certain processes happen. This may explain the dominance of matter over antimatter. Thanks to T-violation, matter creation and antimatter annihilation was preferred over matter annihilation and antimatter creation.
Quote from the article: "CP-symmetry violation is similarly required because otherwise equal numbers of left-handed baryons and right-handed anti-baryons would be produced, as well as equal numbers of left-handed anti-baryons and right-handed baryons."
Violation of the C-symmetry is enough to have more baryons than anti-baryons. The P-violation is needed for the observed right-left imbalance, however theoretically it would be possible to have a P-symmetric world with more matter than antimatter. I don't mean our world. I mean: some hypothetical universe where P is conserved, just to show what P-violation means.
By the way, I just found a perfect example of C-violation in macroscopic world. It's the difference in properties of ions. Anions and cations of the same element have different mass, different size and different probability of being created or destroyed. And this macroscopic violation follows rather directly from the microscopic C-violation. The reason is that we have only one (negative) charge carrier. In a universe with C-symmetry we must have two carriers: positive and negative and (if chemical elements somehow existed) we would have both positive and negative large ions and positive and negative small ions. In our world with broken C-symmetry we have only large negative ions and small positive ions. And it is the direct consequence of the fundamental C-symmetry violation.