{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"04effcddf7c5f992bc5aa4d1bbe98aceb15527f0528cf824ee6b3673e9d2e002","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b","d0ab5819f1c3b3ef3bd220bc093322312f68da8baed3eb76f4554eadf17aec60"],"salt":"2db710faa3727b9d7fb0956fdabb6523bb41a497e7bc579b0144bb33f33e6f3f","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":"2","parents":[],"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 $10^{-18}$, including link noise and the gravitational redshift ($1.1 \\times 10^{-18}$ per cm height), which requires geopotential differences known to $10^{3}\\,\\mathrm{cm}^2\\,\\mathrm{s}^{-2}$.","problem_ref":"d0ab5819f1c3b3ef3bd220bc093322312f68da8baed3eb76f4554eadf17aec60","references":"","settled_by":"An intercontinental clock comparison via free-space optical satellite link, transportable clocks or fiber, with an uncertainty budget below $10^{-18}$ and agreement with independent geodesy.","status_note":"","title":"Intercontinental optical clock comparison at $10^{-18}$","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"4887df24357384be473e505214b1d48640180162e189c5cdd9117a802cc15cdf","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"91cfe643b11702a0c05df77c533a861b44f5106b564b6b736dfa3ab73f9198b2","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"MHc30eUQ3LkidbQx7hQSNXdDHuj9NOnXnWnY3Pfz_5sfJkiPqOCGq4CgR9MsQWEb3qiijCaM7kp_RtYo7Q75Bg"},"schema":"pubphys.envelope/1"},"record_hash":"4887df24357384be473e505214b1d48640180162e189c5cdd9117a802cc15cdf","leaf_index":2270}