[time-nuts] What's the time Mr Wolf...

[Tom Van Baak]

> The tidal effects are much smaller than those from position.  I don't
> think that these effects are visible at the 10-14 or 10-15 level, but
> since I don't know what level they are visible at, I can't be sure.
> I'm sure that someone on this list, maybe as part of their PhD thesis,
> has measured this and can report it :-)
> 
> Warner

Gravitational effects on frequency near the earth are on
the order of 1e-16 per meter of elevation. This level is too
small to measure directly, but if you separate clocks by
say, 1 km, the frequency shift is now 1e-13, which is very
measurable. Since no national timing labs are actually at
mean sea level they all take altitude into account in their
primary standards.

Tidal effects (so-called earth tides) are a couple of ten cm
over 6 hours and thus down in the 1e-17 range. No one has
seen these effects on atomic clocks yet. First, it's just too
small to be measured, even with the best optical clocks, but
second, the nearby reference clock that you use would also
experience the same pull (!) and thus a relative comparison
would reveal nothing.

/tvb