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A 1% measurement would test whether antimatter feels gravity exactly like matter.","posed_since":"","precise":"ALPHA-g measured the vertical acceleration of antihydrogen as $a_g = (0.75 \\pm 0.13 stat+sys \\pm 0.16 simulation) g$ (2023). Determine $a_g/g$ with total uncertainty below 0.01 and test whether it differs from 1.","problem_ref":"d628baec7a47433b74aec7f86b94cddf84f8b50cbd6e05487f18f9dd0e086cf6","references":"","settled_by":"A laser-cooled antihydrogen release or interferometric measurement (ALPHA-g, GBAR or AEgIS) reaching $1\\%$ uncertainty on $a_g$.","status_note":"No measurement of $a_g$ more precise than the 2023 ALPHA-g result has been published as of 2026; antihydrogen laser cooling (2021) is the stated prerequisite for the next step.","title":"Does antihydrogen fall with g to within 1 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