“If you see an antimatter version of yourself running towards you, think twice before embracing.” –J. Richard Gott III
Everywhere we look in the Universe, we find that planets, stars, galaxies, and even the gas between them are all made of matter and not antimatter. Yet as far as we know, the laws of nature are symmetric between matter and antimatter: you can’t create or destroy one without the other.
This question — why the Universe is full of matter and not antimatter — is one of the greatest unsolved problems in theoretical physics. Yet it’s also, conceivably, the one most likely to fall in the coming year! There are four compelling scenarios that might solve this question, that of baryogenesis, that theoretical physics has uncovered, and there’s a good chance that the LHC’s run II will be sensitive to two of them.