From Boing Boing:

The US Air Force is looking into making bombs out of anti-matter. I want a key ring with a speck of it! >One millionth of a gram of positrons contain as much energy as 37.8 kilograms (83 pounds) of TNT, according to Edwards’ March speech. A simple calculation, then, shows that about 50-millionths of a gram could generate a blast equal to the explosion (roughly 4,000 pounds of TNT, according to the FBI) at the Alfred P. Murrah Federal Building in Oklahoma City in 1995.

Sort of interesting, but I suspect that the main point of the Air Force’s research leans more towards antimatter-catalyzed fission then pure “Star Trek”-grade antimatter weapons. An impressively small number of anti-protons can be used to drastically lower the critical mass needed to get a nuclear explosion. This may or may not be useful as a weapon (does anyone actually want grenade-sized nukes?), but it’s fantastically useful as a spacecraft propulsion mechanism. The “orion drive” as it tends to be called in science fiction basically consists of a heavy spacecraft, a thick blast plate, and a bunch of small nukes. Each nuke is thrown out behind the ship and explodes. The blast plate absorbs the blast, and the ship goes flying forward. Repeat a few thousand times, and you’re moving along at a really impressive speed.

Obviously, this works better in science fiction then reality. Niven and Pournelle used it to great effect in Footfall, where they nuked my hometown.

There are tons of engineering and political problems with any sort of nuclear-weapon driven spaceship, but one of the more fascinating ones is that the “classical” version scales up, but doesn’t scale down. You can build immensely huge spaceships with it, but you can’t efficiently build anything much smaller then a flying aircraft carrier, because you can’t build efficient nukes with a small enough yield. That’s where the antimatter comes in–if you can build efficient nukes with really small yields, then this might become practical. It doesn’t solve the political problems, which are probably insolvable, but it brings us closer to being able to efficiently launch large masses into space.