Can someone explain to me how this is going to work in light of the fact that each clock is in a different gravitational field? Or is accuracy not the measurement, but rather stability? No, that can't be because any lab that wants to measure stability merely needs to build two or three copies of their favorite clock and insure against synchronization. They in principle shouldn't need to compare against a dissimilar type of clock. Therefore, we are back to the gravity issue.
When we worked on the 5071A, we barely had enough sensitivity to notice a few parts in 10^13 between Santa Clara and Boulder (~5000 feet). Rick Karlquist N6RK On 6/3/2015 12:18 AM, Hal Murray wrote:
Nice picture: A strontium-ion optical clock housed at the National Physical Laboratory in Teddington, UK. Over the past decade, various laboratories have created prototype optical atomic clocks, which use different elements such as strontium and ytterbium that emit and absorb higher-frequency photons in the visible spectrum. This finer slicing of time should, in principle, make them more accurate: it is claimed that the best of these clocks gain or lose no more than one second every 15 billion years (1E18 seconds) -- longer than the current age of the Universe -- making them 100 times more precise than their caesium counterparts. Optical clocks are claimed to be the best timekeepers in existence, but the only way to verify this in practice is to compare different models against each other and see whether they agree. Starting on 4 June, four European laboratories will kick off this testing process -- the National Physical Laboratory (NPL) in Teddington, UK; the department of Time-Space Reference Systems at the Paris Observatory; the German National Metrology Institute (PTB) in Braunschweig, Germany; and Italy's National Institute of Metrology Research in Turin. Between them, the labs host a variety of optical clocks that harness different elements in different experimental set-ups.
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