Antimatter mystery

THE big bang should have created matter and antimatter in equal amounts, or so our best theories have it. If that were truly the case, though, then the universe would have disappeared in a big puff of self-annihilation almost as soon as it began. The fact that we are here to ponder it tells us something is wrong with this picture (New Scientist, 12 April 2008, p 26). The question is: what?

Experiments in accelerators now tell us that for every 10 billion antiprotons present in the early universe, there were 10-billion-and-one protons. The same tiny imbalance applied to other particles, such as electrons, too. At some point in cosmic history, matter and antimatter met and annihilated. Left behind, those extra particles eventually came together and formed the matter-filled universe we know today. So what created that initial imbalance?

The short answer is that we don't know. One possibility is that antimatter is lurking out there at distant points around the cosmos. That's unlikely, though.

A better idea springs from the weak force, which governs certain nuclear processes, including radioactive beta decay. In 1964, physicists found that the weak force is not quite symmetrical in its dealings with matter and antimatter, resulting in something known as CP violation. This has led particle physicists to suggest that the laws of physics are lopsided. The trouble is that the standard model of particle physics says they aren't lopsided enough. "There is not enough CP violation to do the job," says Frank Close at the University of Oxford.

Other ideas to explain the imbalance of matter and antimatter in the infant universe include a hypothetical particle called the majoron, which is thought to have created neutrinos and antineutrinos, but not in equal amounts. That could eventually have led to an imbalance between matter and antimatter. "If we find majorons at the Large Hadron Collider at CERN," says Close, "then we could hope to study their decays." This would help us discover if they fit the bill.

The 27-kilometre tunnel containing the Large Hadron Collider at CERN (Image: Simon Hadley / Rex Features)