[time-nuts] Re: moving optical clocks to test Einstein's general relativity

[Azelio Boriani]

Is a gravimeter with 1 uGal stability able to support the performance
of optical clocks? Maybe we must first relate the performance of
gravimeters with the performance of optical clocks.
Gravity measurements below 10e−9 g...  <https://arxiv.org/pdf/1809.04908.pdf>
The PTB has made a transportable optical clock that fits in a truck:
<https://www.ptb.de/cms/fileadmin/internet/presse_aktuelles/Presseinfos/2017/D1694_015_komprimierter.jpg>
Geodesy and metrology with a transportable optical clock
<https://arxiv.org/ftp/arxiv/papers/1705/1705.04089.pdf>

On Mon, Nov 13, 2023 at 4:36 AM Attila Kinali via time-nuts
<time-nuts at lists.febo.com> wrote:
>
> On Thu, 9 Nov 2023 13:39:10 -0800
> Tom Van Baak via time-nuts <time-nuts at lists.febo.com> wrote:
>
> > The magnitude of gravitational effects on earth are about 1e-13/km, or
> > 1e-16/m, or 1e-19/mm. Solid earth tides are somewhere around 20 to 50 cm
> > so with optical clocks getting into -18 and -19 levels of precision this
> > starts to be a real effect. I'm pretty sure the experimenters simply use
> > a tide-free geoid model like EGM2008 to make it go away. Note if the
> > clocks are in a similar geographical area earth tides are common mode
> > and so you won't see them. For maximum effect you would want them 90
> > degrees latitude apart (10 000 km at the equator).
>
> To add to this:
> Current optical clock comparisons in Europe are done at the 1e-18 level.
> I.e. where a height difference of 1cm is already significant. At these
> comparisons not only solid earth tides show up, but also the gravitational
> pull of sun and moon, as well as any change in the groundwater level of
> more than 10-20cm. As optical clocks are inching towards 1e-19 stability
> and higher uptimes where comparisons at this level become possible, it is
> very likely that those contributing to TAI will, at some point, install
> gravimeters next to the clocks to constantly account for the shift in
> frequencies. Currently, our comparison capabilities are just not good enough
> to justify this, but it will come. Probably in the near future even.
>
>                         Attila Kinali
> --
> Science is made up of so many things that appear obvious
> after they are explained. -- Pardot Kynes
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