Antimatter falls down
Antihydrogen, released in a magnetic trap, accelerates downward under Earth’s gravity, as ordinary hydrogen does.
Established2 min read
ALPHA-g at CERN held antihydrogen — a positron orbiting an antiproton — in a vertical trap, then let it go. Annihilations on the walls were more frequent toward the bottom. The acceleration is compatible with g, and incompatible with falling up.
General relativity expected this. The experiment was still worth doing, because a repulsive gravitational mass for antimatter would have rewritten the field. It is attractive. Antimatter is not a loophole in weight.
Caveats
- The uncertainty is still tens of percent of g. ‘Down, not up’ is the solid result. A precision equality with hydrogen is the next measurement.
Sources
- 1Anderson E. K. et al. (ALPHA). Observation of the Effect of Gravity on the Motion of Antimatter. Nature 621, 2023.