{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"09ac57c27619d4ab405d0cf22645e224b5624535c313ada78f45ed1e3b71b6e3","created":"2026-10-03T07:17:53Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"b590a012a30446daf3c76c8b311731435ba294219db638a829d84aa7cb126420","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"amo.fine-structure-constant.cs-rb-discrepancy","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"Two labs measured $\\alpha$ by timing how fast an atom moves after absorbing a photon, one with cesium and one with rubidium, and their answers differ by more than five times their stated errors. At least one experiment has an error nobody has found.","posed_since":"2020","precise":"Atom-interferometric photon-recoil determinations give $\\alpha^{-1}(\\mathrm{Cs},\\ \\mathrm{Berkeley}\\ 2018) = 137.035999046(27)$ and $\\alpha^{-1}(\\mathrm{Rb},\\ \\mathrm{LKB}\\ 2020) = 137.035999206(11)$, a $5.4\\,\\sigma$ difference. Identify the systematic effect (or new physics distinguishing the two species) responsible, or produce new $h/m_{\\mathrm{Cs}}$ and $h/m_{\\mathrm{Rb}}$ values that agree at the 0.1 ppb level.","problem_ref":null,"references":"","settled_by":"An independent remeasurement of h/m for Cs or Rb (or both) at below 0.1 ppb with a fully re-evaluated error budget that either reproduces one value or exposes a specific missing systematic.","status_note":"As of 2025 the gap is unexplained and no new h/m result at the required level has been published.","title":"Origin of the $5\\,\\sigma$ gap between cesium and rubidium $\\alpha$","topic_ref":"4128c66497f0d271de4f884d65d6c0eabac35c2b12d26184409fe9547beca009"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"c1cfed59f5ae77039707cf3c1e685d99c0dd73063e074ecc56601fb6cb0252cc","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"6d47ae3835cc38ba13d7f8ff2c4ceddb0190a95dac5916aa7a9b604719d66bd9","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"WF414-sxeglj86Z13dA-ONQyr9pAs16XBNMkX8lLv3qjthgON9C7TXi09PyV01BVk2-vd5QzesMCc5JonZ0ACA"},"schema":"pubphys.envelope/1"},"record_hash":"c1cfed59f5ae77039707cf3c1e685d99c0dd73063e074ecc56601fb6cb0252cc","leaf_index":410}