"Captain, we're runnin' out of antimatter!"
Would antimatter fall if you dropped it? Are the laws of physics
any different for antimatter? Since we haven't really been able to
study it, no one really knows. "In September 1995, a team of
researchers at CERN (European Particle Physics Research Center in
Geneva) succeeded for the first time in making complete antiatoms of
hydrogen, the simplist element. Only nine atoms of antihydrogen were
manufactured in this first experiment, and they each survived for
only about 40 billionths of a second before colliding with ordinary
matter and annihilating. Researchers hope that they will soon be able
to trap antiatoms for long enough to study them (for example, by
probing them with laser beams) and find out if, as present theories
predict, the laws of physics work in exactly the same way for
antimatter as they do for matter."(from Q is for Quantum by John
Gribbin)
Besides the researchers at CERN, there is also a project called
ATHENA in the US who's goal is also to create and trap antihydrogen
atoms. They then want to watch and see if they too will fall under
the force of gravity.
The best-documented "antigravity" effect comes not from laboratory experiments, but from studies of exploding stars and distant galaxies. If the "cosmological constant" people speak of now does exist, and the universe is speeding up, not slowing down, then it would mean there is a latent energy hidden in the fabric of space the counteracts the tug of gravity. Some even speculate that the same energy that gives rise to the "cosmological constant" is also responsible for inertia, which would link the big universal antigravity effect to the potential gravity-fighting techniques on Earth. This could have a lot of possible applications, if it's true, including cool new methods of propulsion. (If you're interested in that, check out the NASA Current Research website.)