[time-nuts] Nature: Hyper-precise atomic clocks face off to redefine time

Richard (Rick) Karlquist richard at karlquist.com
Sat Jun 6 00:19:05 UTC 2015

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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