Many of the startling results obtained in the 20th century about the foundations of physics actually appear in papers produced years before the official discovery. One nice example is the existence of antimatter, which was predicted from symmetries in Dirac's mathematical treatment of quantum field theory and later observed experimentally. However, according to at least some experts, one of Einstein's earliest attempts at a unified field theory actually predicted antimatter as a side effect. Einstein discarded the result, perhaps because he abandoned that attempt as he did all other attempts except the one he was working on at the time of his death.