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Message: <blockquote data-quote="freyar" data-source="post: 6686647" data-attributes="member: 40227">Umbran does a pretty good job breaking down the logical possibilities.  I'd like to elaborate, though, especially because that wikipedia article is a bit disappointing compared to most of the physics wikipedia articles.The most important point to remember is that we really don't know the answer to this question.  It's also quite likely we won't for a long time, since there's very little way to test any of the possibilities --- there are some potentially related effects we can test experimentally, but those are really only good at ruling out options as opposed to pointing toward the correctness of one.This is what people think happens for the most part (I'll explain why below), though how this happens is completely up in the air.  What we do know is that there are several criteria that have to be met (called the Sakharov conditions) and that they are not satisfied (enough) by the Standard Model of particle physics.  In fact, the Standard Model can almost cause a predominance of matter over antimatter, but it would require a certain behavior of the Higgs boson field in the early universe --- and in the Standard Model, the Higgs doesn't behave that way.  To get it to work, you have to add other ingredients to change the behavior of the Higgs.Of course, there are other possibilities.  There could be an entirely new, undiscovered group of particles that are responsible for the excess of our matter. The roots of the excess could happen during inflation.  Or another possibility is that dark matter is also somehow unbalanced between matter and antimatter, and that imbalance gets generated at the same time as the imbalance of normal matter.  There are many different theories.I should also mention that the excess amount of matter is very tiny.  In the early universe, the amount of matter and antimatter was essentially equal.  For roughly every 10 billion matter/antimatter pairs of particles, there was one extra matter particle.  Then all the 10 billion or so pairs annihilated each other away, leaving behind the one matter particle.There's a way this is correct and a way it's not correct, so I want to be very careful here.If we're talking about the decay rates of "everyday" particles and their antiparticles (like protons/antiprotons, neutrons/antineutrons, and electrons/positrons), this is a logical possibility that just doesn't work out.  Based on cosmic ray measurements, the lifetime of the antiproton is at least a million years, which wouldn't leave enough of an imbalance between protons/antiprotons.  Furthermore, there's a mathematical theorem in particle physics that says the total decay rates of particles and their antiparticles must be the same, and any decay of a proton/antiproton generates the same amount of matter/antimatter.  It doesn't work (incidentally, a violation of this theorem would be a super-big deal, meaning we'd have to redo basically all of subatomic physics).On the other hand, it is possible that some very heavy undiscovered particle and antiparticle decay differently into matter and antimatter.  That can happen and can create the imbalance we need.  Of course, we've not discovered such a particle yet.This is an interesting idea, though I confess I've not seen any work related to it.  I also can't immediately think of a way to implement it, either, since, if it's just a "local" fluctuation, it would have to be created during inflation.  Anyway, suffice it to say that I'm not sure if there's a way to get this to work off the top of my head.</blockquote>

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