PHYSICISTS are keen on symmetry. The universe does not always humour them. Take the Big Bang: if nature were ideally balanced, equal amounts of matter and antimatter would have emerged from it. If that were true, though, the universe would be a sad and empty place as almost all the primordial particles and antiparticles would have cancelled each other out leaving behind nothing but a puff of lifeless, post-annihilation photons. That this did not happen, as is clearly the case, is explained by the fact that things are not, actually, quite symmetrical. Instead, a phenomenon called charge-conjugation/parity violation (or CP violation, for short) let matter gain the upper hand.