Ask Ethan: Why does our Universe require CP-violation?

Matter and antimatter are expected to be created or destroyed only in equal-and-opposite amounts, yet the Universe contains almost entirely regular matter with only a negligible trace of antimatter. The visible portion of the Universe is made from Standard Model particles such as quarks, gluons, leptons, and photons, with nearly all of it consisting of protons, neutrons, and electrons. Measured particle physics reactions show that producing or destroying one type of particle requires producing or destroying its corresponding antiparticle in equal amounts. The observed cosmic imbalance therefore requires an explanation tied to CP violation and its consequences for how matter and antimatter behave during creation and annihilation processes.

"Here in our Universe, one great mystery is how, if matter and antimatter can only be created or destroyed in equal-and-opposite amounts, our Universe came to be dominated by normal (regular) matter, with barely a trace of antimatter present. Sure, dark energy (68%) and dark matter (27%) might make up the majority of the Universe, but the rest of it is made up of particles from the Standard Model: quarks, gluons, leptons, and photons. Of that 5%, nearly all of it (4.9%) is regular matter, made of protons, neutrons, and electrons, while the amount of antimatter - like antiprotons, antineutrons, or positrons - is negligible."

"And yet, in every particle physics reaction we've ever measured, matter and antimatter can only ever be created or destroyed in equal amounts: making one proton requires also making one antiproton; destroying one electron requires destroying one positron as well. So what explains the imbalance that we observe everywhere in the Universe: in the Solar System, galaxy, Local Group, and across the entirety of space? That's what Matt Kucera wants to know, specifically asking:"

""Can you help unpack the consequences of that CP violation to explain how it leads to the slight imbalance favoring matter? Does CP violation play a role both in antimatter creation and annihilation?" It's an extremely deep question: one that requires us to go down to the subatomic level to understand the connection between the quantum and the cosmic."

"We don't often think about the cosmic and the quantum being related, and for good reasons. In our everyday experience, quantum mechanics typically only shows up when dealing with extremely simple, small-scale systems: where just a few quantum particles, or quanta, are present within a very small volume of space. Quantum effects often show up when considering the behavior of atoms, protons, electrons, or photons, but not so much when considering larger-scale systems: molecules, cells, rocks, humans, planets, or galaxies."

Read at Big Think