629. I read recently that scientists at CERN produced some form of antimatter, but that it could not be stored. Why can't it be stored and, if it could, would it be a viable method of propulsion? — BC, Ottawa, Ontario
The antimatter that was formed at CERN was an antihydrogen atom, which consisted of an antiproton and an antielectron (often called a positron). Antiprotons and positrons have been available for a long time, but it has been a challenge to bring them together gently enough for them to stick to one another and form a bound system. An antihydrogen atom is hard to store because, like a normal hydrogen atom, it moves or falls so quickly that it soon collides with its container. For a normal hydrogen atom, that collision is likely to cause a chemical reaction. But for an antihydrogen atom, that collision is likely to cause annihilation. When an antiproton touches a proton, the two can destroy one another and convert their mass into energy. The same is true for a positron and an electron. To store an antihydrogen atom, you must keep it from touching any normal matter. That's not an easy task. Because of its ability to emit its entire mass and that of the normal matter it encounters into energy, antimatter is the most potent "fuel" imaginable. But don't expect it to show up in a rocket ship any time soon.