![]() Comparisons of such clocks located far apart such as on different continents could resolve geodetic measurements to within 1 centimeter, better than the current state of the art of several centimeters. NIST’s ytterbium clocks now exceed the conventional capability to measure the geoid, or the shape of the Earth based on tidal gauge surveys of sea level. Applications include relativistic geodesy, which measures the Earth’s gravitational shape, and detecting signals from the early universe such as gravitational waves and perhaps even as-yet-unexplained dark matter. Super-sensitive clocks can map the gravitational distortion of space-time more precisely than ever. While these so-called redshifts degrade a clock’s timekeeping, this same sensitivity can be turned on its head to exquisitely measure gravity. ![]() That is, time passes more slowly at lower elevations. Hence, as we envision clocks like these being used around the country or world, their relative performance would be, for the first time, limited by Earth's gravitational effects.”Įinstein’s theory of relativity predicts that an atomic clock’s ticking, that is, the frequency of the atoms’ vibrations, is reduced-shifted toward the red end of the electromagnetic spectrum-when observed in stronger gravity. “This is especially true because the demonstrated reproducibility shows that the clocks’ total error drops below our general ability to account for gravity’s effect on time here on Earth. “The agreement of the two clocks at this unprecedented level, which we call reproducibility, is perhaps the single most important result, because it essentially requires and substantiates the other two results.” “Systematic uncertainty, stability, and reproducibility can be considered the ‘royal flush’ of performance for these clocks,” project leader Andrew Ludlow said. ![]()
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