[time-nuts] Solving the UTC drift problem

Robert Lutwak Lutwak at Alum.mit.edu
Thu Jul 14 06:44:31 EDT 2005

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.


Robert Lutwak, Senior Scientist
Symmetricom - Technology Realization Center
34 Tozer Rd.
Beverly, MA 01915
(978) 232-1461   Voice           RLutwak at Symmetricom.com   (Business)
(978) 927-4099   FAX             Lutwak at Alum.MIT.edu  (Personal)
(339) 927-7896   Mobile

----- Original Message ----- 
From: "David Forbes" <dforbes at dakotacom.net>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at 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 <a05210601befba18cc387@[]>, 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/
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