Over the past two weeks, scientific results first from Cern and then from an experiment using a nuclear reactor in China have hit the headlines, at least in the world of particle physics. At Cern, in Geneva, antimatter atoms have been studied for the first time by a few dozen scientists working on the Alpha experiment. In China, the Daya Bay reactor, in Guangdong province, near Hong Kong, has been used to confirm that neutrinos might soon be taking centre stage in our understanding of how the universe came to be. Both results touch on one of the biggest unsolved problems in fundamental physics: why is there any matter left in the universe?
It is just as well that there is some matter left behind, because by matter we mean particles such as electrons and protons, the things that build atoms, people, planets and stars. But the situation is a precarious one; for every particle of matter in the universe, there are around a billion particles of light. In other words, the universe is made almost entirely out of light.
The vastly outnumbered matter particles appear to be a tiny residue left over after a spectacular fireworks display that occurred within the first second after the big bang. That fleeting moment saw the production of exactly equal amounts of matter and antimatter, all mixed together in a hot plasma. As the universe expanded and cooled, the anti-electrons started to fuse with the electrons and the antiprotons fused with the protons, converting them into particles of light. In this way, the matter and anti-matter drained away, leaving behind a universe filled with light… except for that tiny residue.
So! does it matter???? something must have have prevented the matter and antimatter from perfect cancellation – and without it we would not be here to wonder about this remarkable universe.