[time-nuts] Primary Time Standards

[Hal Murray]

> One would assume that mean sea level / 1 G would be the standard reference
> point for the "official" Cs transition. I've never seen anybody pull out a
> gravity meter to set up their Cs though. I suspect that NIST has at least
> done the math.

You can do much better than just doing the math.

In 1971, Hafele and Keating put atomic clocks on airplanes and flew around 
the Earth in both directions to check relativity.
  http://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment

GPS satellites have to correct for gravity/elevation as well as 
motion/relativity.  It's enormous on the scale of accuracy expected: 38 
microseconds per day.
  http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

I think the first experimental satellite had the correction turned off for a 
couple of weeks.  It's one of the classic tests of relativity.

---------

This version was more fun:

Project GREAT: General Relativity Einstein/Essen Anniversary Test
Clocks, Kids, and General Relativity on Mt Rainier
  http://www.leapsecond.com/great2005/


-- 
These are my opinions, not necessarily my employer's.  I hate spam.