First collisions at the LHC with unprecedented Energy! (Ask a particle physisicist)

[Alex K]

From the photons and matter in the universe, one can estimate that initially, matter and antimatter were there in almost exactly equal proportions, with a tiny difference like in the 10th digit, giving an advantage to what we call matter. This tiny surplus is what we are made of today, while all the rest annihilated to photons, which subsequently were redshifted.

People are thinking about particle physics mechanisms how one could produce the observed tiny surplus of matter from an equilibrium after the Big Bang, and already 50 years ago, a russian guy named Sakharov, who was also involved in the soviet nuke but later became a kind of pacifist, he identified what conditions have to be met in order for such a surplus to arise - the fundamental laws of physics must have a slight asymmetry between matter and antimatter (such that they aren't exact mirror images of each other), there must be a violation of so-called baryon number (because otherwise, for each proton that is created, you'd have an antiproton), and the universe must be out of thermal equilibrium because in thermal equilibrium, any differences get erased. Those are the Sakharov conditions. The question is now, what is the exact particle physics mechanism in nature which accomplishes this. There are several proposals on the table, and it would be nice if one could study this mechanism at colliders to determine which one of them is maybe correct, or none. It is however not clear whether that is possible. Some of these proposals rely on new particles that would be observable at the LHC at some point.

That makes sense.

I read somewhere that the leading theory for why there is no antimatter (probably dumbed way down) was that at the moment of the Big Bang, there was slightly more matter than antimatter, and the two annihilated each other, leaving only the excess matter left over.

Why is it a mystery that there's none of something that doesn't exist?