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Comment by Panoramix | Hacker News Reader

Sorry but that last sentence of yours doesn't make sense to me. From the discovery that it is created frequently on Earth, it does not follow that it won't exhibit any interesting properties nor that it is common in the universe (except by a generous definition of "common"). Anyhow, the main mystery remains: the Universe should be 50% matter and 50% antimatter, so where has all the antimatter gone?

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> the Universe should be 50% matter and 50% antimatter

Out of curiosity, where does this come from?

The big-bang did not create particles or atoms, merely energy. In the very initial stages of the big-bang all of the mass of the entire Universe was locked up in bosons (photons, W & Z bosons, etc.), with virtual quarks and other exotic particles existing only ephemerally. At this stage the Universe is essentially an enormously hot photon gas. As the Universe cooled lower energy particles (such as electrons and protons) became more stable, and more and more energy started to become locked up in them. Interactions involving high energy photons can create particle / anti-particle pairs, in theory these should be exactly balanced. However, in practice it appears as though there is much more matter than anti-matter in the Universe. Likely this is due to some slight imbalance in particle/anti-particle pair creation, but we do not sufficiently understand this (though there have been a few hints).

I think that's a good question. It is natural to require that the total charge in the universe was zero at the start of its life (same goes for all quantum numbers). Otherwise, there was something before there was anything! Seriously, either this matter-antimatter asymmetry was an initial condition (in which case we can't hope to understand it) or it appeared at some point during the course of things.

The problem of finding the exact mechanism that gave us the matter-filled universe we observe today, with all the antimatter gone is an open question. There are a bunch of hypotheses, and experiments coming son to a large hadron collider near you will help physicists gather pieces of the puzzle.

Thanks (both you and InclinedPlane), I guess that makes sense.

I thought there were some theories that early-universe physics were very different from what they are now, though I'm not sure how that would help.

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