{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"7df465f6c999c9f32663361b052a9b4e91a8ba280bfe522f241c132e21579dbd","created":"2026-10-03T07:17:54Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011","7f40ff2864398d0b188c2132ef7ad3152dc9fb621b66d148e7d5fc999667a4bf"],"salt":"0ad9ecdb7d1bcb0a411b88977b2eee7cc5f62bb8b86ad415c08d3e07e10a11b1","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"amo.optical-clocks-second.remote-comparison","kind":"well-posed","literature_status":"open","n":"1","parents":[{"note":"","parent_revision":"7f40ff2864398d0b188c2132ef7ad3152dc9fb621b66d148e7d5fc999667a4bf","relation":"special_case"}],"plain":"Clocks on different continents must be compared to check that they agree, but satellite links are not yet good enough. Height differences also matter, since a clock 1 cm higher runs faster by about one part in $10^{18}$.","posed_since":"","precise":"Achieve a comparison of optical clocks separated by more than 5000 km with total uncertainty below 1e-18, including link noise and the gravitational redshift (1.1e-18 per cm height), which requires geopotential differences known to $1e3\\,\\mathrm{cm}^2\\,\\mathrm{s}^{-2}$.","problem_ref":null,"references":"","settled_by":"An intercontinental clock comparison via free-space optical satellite link, transportable clocks or fiber, with an uncertainty budget below 1e-18 and agreement with independent geodesy.","status_note":"","title":"Intercontinental optical clock comparison at 1e-18","topic_ref":"5d572b616becc2d77dc7833412720dbdbc6e7e6aa45f95467fa95e2923acf321"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"d0ab5819f1c3b3ef3bd220bc093322312f68da8baed3eb76f4554eadf17aec60","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"50f04b2702e261f0c31ffba691fcc21236f648ad207d8fefd11808ed0e95c91a","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"bAGP3PuUC4eVz9CxiDabA6Mtj39jQhldnM0ORmWyeqV962noKgb4RbW2hYSBzBq6wKj2fGHuOFsO9n-Di6p5Bw"},"schema":"pubphys.envelope/1"},"record_hash":"d0ab5819f1c3b3ef3bd220bc093322312f68da8baed3eb76f4554eadf17aec60","leaf_index":444}