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

[Tom Van Baak]

Eric,

Thanks for posting that link. Andrew Ludlow of NIST presented last week 
at the SCPNT conference. The video / slides aren't up yet. Note their 
mountain-valley experiments are direct comparison of optical clocks via 
lasers which makes it possible to measure the effects of relativity on 
clocks in real time. A related NIST experiment was done between two 
Hawaiian islands a few years ago.

Without direct laser, copper, fiber, or RF links I had to drive my 
clocks up a mountain, stay a day or two, and then return for the 
comparison with clocks left down below. That round-trip method works 
because 5071A are portable. Currently optical clocks are stationary or 
"transportable", but not portable. By transportable I mean one can build 
an optical clock as a self-contained instrument rack so that it can be 
moved and set up at different locations. By portable I mean you can move 
it while still running with no loss of lock. That allows one to "carry 
the time" instead of just having a frequency standard.

John,

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).

/tvb


On 11/6/2023 6:57 PM, Eric Scace via time-nuts wrote:
> Updating the TVB mountaintop experiments with optical clocks on the continental divide here in Colorado...
>
> <https://www.colorado.edu/ecee/2023/11/01/researchers-test-einsteins-predictions-general-relativity-atop-rocky-mountains>

On 11/9/2023 7:12 AM, john.haine--- via time-nuts wrote:
> This raises an interesting question - will this be sensitive enough to
> detect tidal changes in gravity?  Indeed, are caesium clocks able to do
> this?  We know of at least two pendulum clocks that could - the Shortt Free
> Pendulum and the Fedchenko.