[time-nuts] Cesium Clocks and Relativity (Project GREAT)

Tom Van Baak tvb at leapsecond.com
Sat Dec 9 10:15:59 EST 2006


First a little humor:

    http://www.leapsecond.com/pages/atomic-tom/

There is an atomic clock experiment I've wanted to do
for years.

I assume many of you know that, according to Einstein's
special theory of relativity, clocks moving fast run slower.
Similarly, according to his general theory of relativity, even
stationary clocks in a stronger gravitation field run slower.

It follows then that clocks at rest on a mountain run faster
than clocks at rest near sea level. It's a tiny amount, to be
sure: the effect is about 1e-16 / meter; which is why none
of us really notice it with our cesium clocks at home.

Since the 1970's when cesium clocks got stable enough,
and portable enough, this relativistic effect on clocks has
been demonstrated many times. You may have read about
the USNO east/west round-the-world flying clock experiment
by Hafele & Keating, or the airplane altitude experiments
by Alley, or the NASA rocket experiment by Vessot.

You could call these guys professional time-nuts and their
experiments are now classic. Of course, today we have
things like GPS which indirectly demonstrate SR and GR
continuously. And BIPM routinely compensates for altitude
in the national laboratory's primary standards into the UTC
calculation.

Anyway, ever since hearing about clocks and relativity I
wondered if it was possible for an amateur to pull off one
of these flying or traveling clock relativity experiments.

Could one of us actually see the effects of GR on our
atomic clocks? Or is the effect too small? Are the surplus
cesium clocks we get on eBay accurate enough? What
would it take to measure it? To me, seeing, measuring,
and proving relativity was always a kind of holy grail of
an amateur precise time hobby.

So that's what Project GREAT is all about. Please feel
free to offer comments or ask questions. While I finish
writing the paper, you'll find the abstract of the talk and
a few photos here:

    http://www.LeapSecond.com/great2005/

The rest of the content will appear shortly.

/tvb




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