Antihydrogen Falls Down: The ALPHA-g Measurement and the Equivalence Principle for Antimatter in the Frame

In 2023 the ALPHA-g experiment released antihydrogen from a magnetic trap and watched which way it fell: the antimatter accelerated downward at 0.34 to 1.16 of ordinary gravity (two-standard-deviation interval), with a central value of 0.75 g and a combined uncertainty of 0.21 g (Anderson et al. 2023). The result excludes antimatter being repelled by gravity and agrees with the equivalence principle within 1.2 standard deviations. The frame predicts exact equality, since its torsion couples to energy-momentum regardless of the matter-antimatter distinction; the present measurement already bounds any anomalous antimatter coupling to an anomalous fraction of 0.41, and the experiment's planned percent-level precision will test the prediction at a level where frame variants with charge-asymmetric couplings would be separated. Computed from published results, not measured.