Particle physicists believe they have uncovered the reason why our Universe favours matter, instead of being made up of equal parts matter and antimatter. Their experiment was done with the Stanford Linear Accelerator Center (SLAC) in the USA, which collides electrons and antimatter positrons together to produce a spray of exotic particles. Although complete opposites, the various particles and anti-particles should have similar decay times, but the experimenters found that the anti-particles seem to decay much quicker.