Intercontinental optical clock comparison at $10^{-18}$
In plain words
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 $10^{18}$.
Precise statement
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 $10^{3}\,\mathrm{cm}^2\,\mathrm{s}^{-2}$.
What would settle it
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.
Parent problems
- Special case of Can optical clocks meet the redefinition criteria by 2029? · open · from revision 1 The parent was revised since revision 1: it now states another question.
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