{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"b1801f4d594f2461ebdf883f026229cc8d1dc2aa2296ad4fc5473c5c266fdb0d","created":"2026-10-03T07:17:54Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"edf6a5aa064b79f2f0be5e4eb595010407bae5e7b49547bae3db39acd9b2521a","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"amo.quantum-equivalence-principle.antihydrogen-fall","kind":"well-posed","literature_status":"open","n":"1","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 +- 0.13 stat+sys +- 0.16 simulation) g (2023). Determine $a_g/g$ with total uncertainty below 0.01 and test whether it differs from 1.","problem_ref":null,"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":"1ef36fc0692a8bd1d924ba5b2faf894c475adb1314f3440a6281df6c8bcb9e1b"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"d628baec7a47433b74aec7f86b94cddf84f8b50cbd6e05487f18f9dd0e086cf6","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"a1aa51a99e0c4c3b9e7528bb6cebddce6289d3848c1dff952a5a1020a253d97a","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"I9w3fqUX12tQTFLX_68YCqpmd1f-ScLKb5Jt-v-D_gAnNCa8IcMyceEA2ntD_lcqTz1iMTmoETTSqS_PDA9FDw"},"schema":"pubphys.envelope/1"},"record_hash":"d628baec7a47433b74aec7f86b94cddf84f8b50cbd6e05487f18f9dd0e086cf6","leaf_index":447}