I had a thought the other day regarding this "mystery". First, assume MWI is true (for the sake of the argument). If MWI is true, then all universes that have some probability of existing given the initial conditions of the big bang do exist. Now imagine that the symmetry between matter and anti-matter exists as well. That is, the expected amount of matter in the universe is equal to the expected amount of anti-matter. Now assume there is some process that allows for the creation of only matter or anti-matter, with a 50/50 chance of either. Although a vast majority of the universes will have equal amounts of matter and anti-matter, some small percentage will be dominated by either matter or anti-matter. In a universe with equal parts matter/anti-matter, life can't exist since they would annihilate and there would be no matter or anti-matter. Since we can only exist in a universe where one is dominated by the other, that is the class of universe we live in. If this were true, asking "why is there so much matter and no anti-matter?" would be meaningless since the only way to ask why is if its true. I made two assumptions here. 1) MWI is true. However, this can be replaced with the anthropic principle. Whether or not those other universes exist, the only way for us to exist is if the universe is dominated by 1 type of matter. 2) there exists some process that creates either only matter or only anti-matter. This one Im less sure about but I thought of a process that has no immediate problems that I can see. gamma -> 4 anti-neutrinos + 1 electron + 1 proton. Im not sure if this is valid, but it does preserve the lepton, strange, energy, momentum, charge, and spin conservation laws (if it doesn't preserve energy and momentum that adding more photons at the beginning would). Although this does produce anti-matter, it produces it in the form of neutrinos and allows an electron and a proton to be created without their anti-matter counter-parts. Im pretty sure my argument is consistent with the assumptions, and I'm pretty confident in the first assumption (MWI or anthropic principle). Is the second assumption correct (for some process, not necessarily the example I gave)? And if it is doesn't this provide a reasonable explanation for why the universe is primarily matter??