Most of the world's atomic clocks are employed as frequency standards. In
addition to the telecom applications, they are used in positioning and
navigation, precision measurement, and, yes, a few for timekeeping. Those
who care for time to be synchronized with the sunrise are relatively small
in number, mostly astronmers who don't want to recalculate sunrise every
year or two.
Since the official definition of the speed of light, in 1983, and the
subsequent redefinition of the meter in terms of the speed of light and
time, all precision length measurements (think international commerce) are
also determined by the cesium frequency. The last "artifact" standard is
mass, which will likely be redefined soon in terms of the density of pure
silicon crystal, thus tying it also to length and thereby frequency.
Perhaps most importantly, as TVB points out, there are hundreds (or perhaps
thousands) of other precision measurements, of atomic and physical
properties, measured in terms of precise frequency. Any change in the SI
second would be catastrophic to the world of precision measurement,
calibration, and international commerce.
There is no UTC drift problem. The only "problem" is the gradual slowing of
the earth's rotation due to tidal forces (which, by the way, is expected to
change sign in about 75 years), leading to this historic need to add leap
seconds occasionally for those who insist on watering their tomato plants at
sunrise (as determined by their home cesium clocks). Except for these nuts,
leap seconds are a pain-in-the-butt for anyone else doing timekeeping,
timetagging, or frequency measurement.
-RL
------------------------------------------------------------
Robert Lutwak, Senior Scientist
Symmetricom - Technology Realization Center
34 Tozer Rd.
Beverly, MA 01915
(978) 232-1461 Voice [EMAIL PROTECTED] (Business)
(978) 927-4099 FAX [EMAIL PROTECTED] (Personal)
(339) 927-7896 Mobile
----- Original Message -----
From: "David Forbes" <[EMAIL PROTECTED]>
To: "Discussion of precise time and frequency measurement"
<time-nuts@febo.com>
Sent: Thursday, July 14, 2005 3:15 AM
Subject: Re: [time-nuts] Solving the UTC drift problem
At 8:25 AM +0200 7/14/05, Poul-Henning Kamp wrote:
In message <[EMAIL PROTECTED]>, David Forbes writes:
A modest proposal:
Instead of adding randomly-placed leap seconds to UTC or allowing UTC
to drift from UT1 etc, the timing community should just change the
second's definition from time to time as needed. That is, dither the
Cs transition frequency between 9,192,631,770 Hz or ,780 Hz annually
to make time speed up or slow down to match the earth's rotation.
That has already been tried (1958...1972) It was not a success.
I can see that it was not a success at the time, but the equipment of the
time was rather primitive compared to today's digitally programmed
electronics. It used to be difficult to synthesize a microwave signal with
10 Hz resolution; now it's done in less than a square mm of silicon.
However, the argument presented in the Metrologia article that physicists
would not have a fixed SI unit called the second is a valid concern.
The beauty of this method is that there are only a few hundred Cs
clocks in the world,
This number is probably one or two orders of magitude to low, but
a lot of them are telecom timers so they can be ignored.
Tee hee. Yes, they don't what a second is, as long as each clock is
consistent with the clock at the other end of the fiber.
Symmetricom would love this idea, as they would get to sell a lot of
upgrade kits at monopoly prices.
--
--David Forbes, Tucson, AZ
http://www.cathodecorner.com/
_______________________________________________
time-nuts mailing list
time-nuts@febo.com
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
_______________________________________________
time-nuts mailing list
time-nuts@febo.com
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
