ANTIMATTER

Just one second after the birth of the Universe, space was flooded with particles and over the next 300 million years stars and galaxies began to evolve into the kind of cosmic landscape that we recognise today. But there's one big problem. We shouldn't really be here. People, planets, stars, galaxies should all be impossible dreams. In theory, nothing should exist.

According to physics, the Big Bang should have produced matter and its nemesis, antimatter, in equal quantities. Antimatter is the 'mirror image' of matter, being the same size, but having opposite properties such as electrical charge. Because of their differences, when these two adversaries meet they completely annihilate each other, resulting in a brilliant flash of light. So, by rights, early on in the history of the Universe all the matter and antimatter should have exterminated each other, leaving nothing apart from an afterglow from these cosmic fireworks.

We've never seen a substantial amount of antimatter anywhere in the Universe. It's possible that there may be antistars or antigalaxies out there that are entirely made up of antimatter, but that are stable because they have never come into contact with matter. In fact, if we ever find aliens and decide to meet up, we'll have to check first that they aren't made from antimatter, otherwise it could spell doom for both of us.

So it seems obvious that there is more matter in the Universe than antimatter. There is matter all around us, but we haven't spotted much antimatter anywhere. But how did this imbalance happen if both particles were created in equal amounts? No one is sure for certain. But particle physicists think that this excess matter was left because antiparticles might not be the exact opposite of particles. This was first discovered in the early 1960s by James Cronin and Val Fitch, who won the Nobel Prize for their work on a certain type of particle called the kaon.

Physicists now think that kaons might live longer than antikaons, but they're still not sure if this accounts for the triumph of matter over antimatter in the Universe. In order to probe these mysteries, physicists produce antimatter by smashing particles together in huge laboratories called 'particle accelerators'. They can then recreate the environment of the early Universe in order to investigate this preference for matter over antimatter. By recreating these ancient battles, physicists hope to fathom out why we managed to survive.