[time-nuts] Re: gravity fields affect time keeping?

[Peter Monta]

Hi Marek,

> Anybody studied the influence of the Sun's gravity on clocks in GNSS satellites? The field might change slightly by 40,000 km distance when the sat is closer to the Sun than later on the opossite side of Earth. Is this measurable on the clocks?

It seems this effect is below the noise floor of the current clocks. See this paper:

https://link.springer.com/content/pdf/10.12942/lrr-2003-1.pdf

Here's the relevant text:

> Effect of other solar system bodies. One set of effects that has been “rediscovered” many times are the redshifts due to other solar system bodies. The Principle of Equivalence implies that sufficiently near the earth, there can be no linear terms in the effective gravitational potential due to other solar system bodies, because the earth and its satellites are in free fall in the fields of all these other bodies. The net effect locally can only come from tidal potentials, the third terms in the Taylor expansions of such potentials about the origin of the local freely falling frame of reference. Such tidal potentials from the sun, at a distance 𝑟 from earth, are of order 𝐺 𝑀_sun 𝑟^2/ð‘
^3 where ð‘
 is the earth-sun distance [8]. The gravitational frequency shift of GPS satellite clocks from such potentials is a few parts in 10^16 and is currently neglected in the GPS.

​
Maybe future GNSS with optical clocks (or advanced Cs clocks) could get to this level.

Cheers,
Peter