Antimatter matters

摘要

Why is the known Universe made of matter and not antimatter, if, as we believe, both were created in equal quantities in the Big Bang? An asymmetry in the behaviour of matter and antimatter at the particle level may be part of the answer. Experiments studying the decays of particles called B mesons are casting new light on this asymmetry. Although some results are puzzling, most agree with the predictions of a model, devised by Makoto Kobayashi and Toshihide Maskawa, of an effect known as CP violation. The balance between matter and antimatter has been an issue since 1928, when Paul Dirac pointed out that the existence of antimatter was an unavoidable consequence of combining the theories of relativity and quantum mechanics. But where was the antimatter? Initially, there was speculation that the proton might be the antiparticle of the electron, despite its different mass and manifestly different properties. Once the true anti-electron―the positron―was detected in cosmic rays by Carl Anderson in 1932, serious business could begin.