In a big pit at CERN, the European Institute for Nuclear Research in Geneva, a particle accelerator churns out antimatter that has the potential to treat cancer. A California company, PBar Labs, is sponsoring experiments to determine if antimatter can zap tumors in hamster cells. If this therapy works, plans are to treat human cancers. Unlike conventional radiotherapy, antimatter can be precisely calibrated to destroy only cancer cells. And as antimatter doesn't travel far in air, patients wouldn't need much shielding. The accelerator's proton source is a heavy target like tungsten. In the accelerator, these protons collide. Each million-proton collision generates one proton-antiproton pair. Physicists separate the antiprotons from the rest of the soup and slow them down in an antiproton decelerator shaped like a 100m-diameter doughnut swathed in foil and duct tape. The antimatter particles annihilate when they encounter matter, thus they can only be stored suspended in a vacuum. Antiprotons can be precisely targeted so that only in the last millimeter of their path (i.e., in the tumor) they slow down, interact with an atom and are annihilated. "The body is basically empty space," says Michael Doser, a physicist on the project who looks as if he were sent straight over from Hollywood casting. "All matter is illusion. To an antiproton, the body is just an array of atoms. Atoms consist of a tiny nucleus surrounded by a huge cloud of electrons. Antiprotons interact only with the nucleus. If you randomly kick a football through a field that only contains one other football, it is unlikely to hit anything, Doser explains.