[ntp:questions] National time standard differences
unruh at wormhole.physics.ubc.ca
Fri Feb 12 18:08:00 UTC 2010
On 2010-02-12, John Ackermann N8UR <jra at febo.com> wrote:
> David J Taylor wrote:
>>> The flying clock tests were closed loop (I think there's a more
>>> accurate term for the process) where the clock, including both its
>>> initial time error and its frequency offset (rate difference from USNO
>>> or NIST), was well characterized via radio and against a set of
>>> similar clocks prior to take-off. At the end of the trip, the clock
>>> was measured again. The time difference between departure and arrival
>>> was proportionally applied to the measurements taken along the way.
>>> e.g., if the clock was known to be 10ns/day fast during the trip, you
>>> adjust a measurement made on the 3rd day by 30ns. There were lots of
>>> additional statistics applied to improve the measurement results.
>> Thanks, John. Was the measurement down to the nanosecond level?
> Hi David --
> I haven't had a chance to review the article about the 1964 trip, so
> don't recall all the details, but I know that the HP advertisement about
> the experiment had a tag line that after seventeen days or whatever,
> "somewhere along the way we lost a microsecond." So they clearly were
> measuring at sub-microsecond levels.
> That first experiment was done with HP 5060A cesium standards and there
> have been several generations since; the HP 5071A that's been available
> since the early 90's is perhaps three orders of magnitude better than
> the 5060A.
> BTW -- someone cited a paper showing relativistic effects of a
> round-the-world flying clock trip in both directions. That, I believe,
> was done with the 5071A. Another great experiment -- done by an amateur
> time-nut, Tom Van Baak -- took three 5071As on a camping trip up a
> mountain in Washington state and verified Einstein's prediction of a
> change in clock rate with elevation. Take a look at
> http://www.leapsecond.com/great2005/index.htm and be amazed.
That's about 2Km, which is a time difference of 2 parts in 10^-13. Ie,
if he was up there a day, the time difference would be 10ns. I wonder if
they are really that accurate.
The ultimate was the Vessot experiment in which a H maser clock was shot
up to 10000Km and the special relativisitic and general relativistic
time shifts were measured.
Bender claims that the GPS engineers did not believe that GR was real,
and had a software switch which they could use to eliminate the General
Rel corrections in the GPS.
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