On 2/11/10 11:45 AM, Richard B. Gilbert wrote:
unruh wrote:
Since the flight probably lasted say 10 hr, which is 100000 sec, th
eclocks would have been out by about 1usec. Assuming that the clocks
could then have been synchronized, that would mean that US and
Switzerland time have been out by about 1usec. (Why they would fly
from
Palo Alto when the time standard is in Washington DC I have no idea).
Probably because the clocks came out of the HP Palo Alto office?
But if they are comparing time standards, it does not matter where the
clocks were manufactured, but where they are synchronized with the time
standard, and that is surely in Washington, not Palo Alto. You do not
try to synchronize a clock in Washington via phone lines or
microwave links with Palo Alto surely.
ISTR that NIST has facilities in both Colorado and Hawaii. The
Washington DC area has the U.S. Naval Observatory.
People might want to look at articles at
http://www.leapsecond.com/history/
(A fun site! )
The 1965 "Cesium Beam ..." article:
In June 1964, two commercial cesium standards which
had been taken to Switzerland for an instrument
exhibition were compared with the long cesium
standard at LSRH in Neuchatel (BAGLEY and CUTLER,
1964). Four days later the commercial instruments
were measured in terms of the NBS standard in
Boulder, Colorado, after being kept in continuous
operation during the intervening time. The results of
these measurements again showed the Swiss and U. S.
standards to be in agreement to better than 1 X 10-11.
The assumption of perfect stability of the commercial
standards between comparisons did not appear to
timit the measurements in view of the excellent longterm
stability demonstrated by these instruments
during one week's continuous operation in Switzerland.
and at the end of the article:
... Clocks
based on these time scales have been synchronized over
intercontinental- distances by clock-carrying experiments,
use of radio transmissions, and use of artificial earth satellites.
Accuracies of the order of 1 microsecond have been achieved.
The site also lists a 1978 article and notes "This is the earliest
reference I've found to the relativistic corrections needed for GPS."
Ah.. you can read all about the experiment in
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1964-07.pdf
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