2002: thousands of cold antihydrogen atoms

Two CERN experiments, ATHENA and ATRAP, took a major step towards understanding antimatter in 2002 by creating thousands of atoms of antimatter in a �cold� state. Cold means that the atoms are slow moving, which should make it possible to study them before they meet ordinary matter and annihilate.

In the experiments the antihydrogen formed when cold positrons and antiprotons were brought together and held in a specially designed �trap�. Once formed, the electrically neutral antihydrogen atoms drifted out of the trap and annihilated. The next challenge will be to devise a means to trap the neutral antihydrogren.

Cold antihydrogen will be a new tool for precision studies in a broad range of science. Most fundamental will be the comparison of the interaction of hydrogen and antihydrogen with electromagnetic and gravitational fields. Any difference between matter and antimatter, however small, would have profound consequences for our fundamental understanding of Nature and the Universe.