We wouldn't expect to find large pockets of antimatter in our universe, but cosmologists are testing for their presence in cosmic rays. "Because we're surrounded by regular matter, we make the assumption that the universe as a whole is dominated by matter. But we can't be absolutely sure about that, and this is where antihelium-4 enters the picture. ... It's these improbable pockets of antimatter that we're about to start looking for. The space shuttle Endeavour's final mission will include bringing the Alpha Magnetic Spectrometer to the International Space Station, where it will begin looking for antimatter particles in cosmic rays. If we live in a matter-dominated cosmos, Alpha shouldn't detect any anti-helium at all."