Can antimatter fall upwards?

The video explores two experiments designed to test how gravity affects antimatter. The first experiment, Alpha G, involves trapping antihydrogen atoms in a vertical vacuum chamber to observe gravitational effects. The second experiment, G Bar, tests antihydrogen atoms generated from antiprotons by subjecting them to a 20 cm fall. Scientists predict that antimatter should behave like regular matter under gravity, but there's a small chance it could behave differently.

How will the effect of gravity on antihydrogen atoms be tested in the experiments?

What is the significance of the one in a million chance mentioned in the text?