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

Attila Kinali attila at kinali.ch
Sat Jun 6 13:32:05 EDT 2015

Hoi Rick,

On Fri, 05 Jun 2015 17:19:05 -0700
"Richard (Rick) Karlquist" <richard at karlquist.com> wrote:

> 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.

They are not there yet. Although the clocks achieve stabilities
down to 1e-17, the current comparison methods do not yet allow them
to measure down to that scale where gravity matters (although, it's
just barely, a bit better and they need to compensate for it).
That is the main reason why they are building fiber lines between the
different labs in europe.

The other thing is, they know approximately what the gravitational fields
at the different labs are. My guess is that this already has a low
enough uncertainty to make other uncertainties higher.

I also guess, that this is mostly a test run for the real system which is
being build, to figure out whether they have any systematics that are not
yet accounted for.

There was a talk on different comparison methods and how accurate they
are at last years EFTF. If you want I can dig out the paper.

			Attila Kinali

It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson

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