How much does antimatter weigh?

Antimatter is mysterious, dangerous, and rare. In fiction, it's at the core of Isaac Asimov's positronic brains, the engines on the Enterprise, and the bomb in Dan Brown's Angels and Demons. But in the real world, antimatter is fairly mundane stuff. If the entire universe turned into antimatter, we'd barely notice. Or… » 5/08/13 1:00pm 5/08/13 1:00pm