[time-nuts] Pendulums & Atomic Clocks & Gravity

[Brooke Clarke]

Hi:

Just starting to adjust the bob on a pendulum clock, see:
http://www.prc68.com/I/SWCC.shtml
and doing some calculations regarding the pendulum.  Which soon leads to the 
value of "g".  This can be found for U.S. locations using an on line calculator 
at: http://www.ngs.noaa.gov/cgi-bin/grav_pdx.prl (need Lat, Lon, elev)

Then a pendulum calculator at:
http://www.ajdesigner.com/phppendulum/simple_pendulum_equation_period.php
allows solving any of 8 pendulum related equations.

Tom has pointed out that the stability limit on pendulum clocks is in the area 
of 1E-7 because of the complex effect of the Sun and Moon on the value of "g".
http://www.leapsecond.com/hsn2006/ch1.htm

Gravity also effects atomic clocks, see: http://www.leapsecond.com/great2005/
and this puts a limit on what can be done with any atomic clock that's on 
Earth.  "g" will always have minor fluctuations (noise) due to all sorts of 
things like the Sun, Moon, planets, asteroids, earthquakes, etc.  It's still a 
direct "g" effect called red shift like (U2 − U1)/c2, where the Us are 
gravitational potentials, only smaller by c squared.

I expect that in not too many years the official master clocks will no longer 
be on Earth, but instead in satellites.  There "g" is precisely known to be 
zero.  Since GPS satellites are excellent for time transfer that's where they 
will be.  The ensemble will be the full constellation.

In "Time Too Good to Be True" Kleppner
http://www.physicstoday.org/vol-59/iss-3/p10.html
says "...a primary standard in space would not overcome the problem of 
comparing time or frequency at different locations on Earth."

I don't understand why that would be the case with a standard in a GPS 
satellite.  Granted E-18 can not now be done using the current GPS system, but 
when atomic clocks get into the E-16 or better area and are in satellites, I 
think the quality of time transfer will keep up.

Just an idea & Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com