[time-nuts] Cesium vs H Maser clocks

[Mike S]

At 01:30 AM 11/29/2008, Tom Van Baak wrote...
>Note also that clocks at NIST run about 1.8e-13 fast due to the high
>elevation of Boulder, CO (general relativity), which is yet another
>factor that has to be corrected for compared to the official sea-level
>definition of the second.

Do they really adjust to sea level on earth? That isn't part of the 
definition. Within that convention, as the mean sea level rises (~20 cm 
in the last 100 years), does the length of the second change 
(relatively)?

Relativity tells us that time can be different in different reference 
frames, and that no frame of reference is unique. The NIST Cs clocks 
may differ from others, but they run perfectly (after adjustment for 
radiation effects), by definition. I understand that some practical 
uses of time (e.g. GPS) require that clocks in different reference 
frames be synchronized, but then a paradox is created, since even 
though different, both are correct.

"The second is the duration of 9 192 631 770 periods of the radiation
corresponding to the transition between the two hyperfine levels of the 

ground state of the caesium 133 atom." "This definition refers to a 
caesium atom at rest at a temperature of 0 K." - 
http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf

What does "at rest" mean, other than that the definition applies to 
only the local frame of reference (i.e. observers to whom the atom 
appears at rest)? There is no absolute rest, which is what special 
relativity addressed.

Finally, at "0 K," "at rest," (is there a difference?) how is 
_anything_ happening with that atom? Doesn't time actually stop? You 
can't reach 0 K anymore than you can accelerate a mass to C.