{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"6841e34c2b087b78b9ba7ddadd6cb2fb7d97fe2c7910b3faf86781469160a853","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":["ai:gpt-5.5"],"kind":"seed"},"parents":["ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b","d628baec7a47433b74aec7f86b94cddf84f8b50cbd6e05487f18f9dd0e086cf6"],"salt":"869beb6faf053dbef408ba310b9f55af84cc9b077fd0400663ba9e73d7d5704d","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":["ai:gpt-5.5"],"external_id":"amo.quantum-equivalence-principle.antihydrogen-fall","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"In 2023 the first direct experiment showed that antihydrogen falls down, not up, but only to about 20% precision. 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 percent?","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"ce771d8afc2b8de3c8b15cb9b02217f45e2591348e1bd0fe7116c1ad10a154f4","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"7363cd3e77df120fa17492f6eb1a3ce14c24d38e2ba024f1a8e6246b4d43775a","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"YoQJ8kn704FmIE-4dFS-Pu2Dkhpck7A64NFkbP1HzZ_q9VH114oEq-BbHGRGQFNQFLUy9ZdxVFjROcr3NNKuDg"},"schema":"pubphys.envelope/1"},"record_hash":"ce771d8afc2b8de3c8b15cb9b02217f45e2591348e1bd0fe7116c1ad10a154f4","leaf_index":2276}