# [time-nuts] Solving the UTC drift problem

Dr. David Kirkby drkirkby at medphys.ucl.ac.uk
Thu Jul 14 11:47:40 EDT 2005

```David Forbes wrote:
> 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.
>
> After all, that 9,192,631,770.0 Hz frequency is an arbitrary number. It
> just happened to be close to the MST-derived second in 1967, rounded to
> the nearest 10 Hz.

I just checked the date and see it is not the first of April, so I'll assume this is not a joke -
although perhaps it is. (The first time I read about Silicon Germanium was in an April issue of some
magazine, and I was convinced it was a joke, but it was not. So perhaps I got it wrong here too)

You propose taking something that is stable (the duration of 9,192,631,770 periods of the radiation
corresponding to the transition between the two hyperfine levels of the ground state of the caesium
133 atom) and replacing it with something less stable.

Redefining the second in terms of something more stable (hydrogen maser) would be progress, but that
is not progress.

> Am I missing something?

Have you thought about the consequences?

The metre is currently defined as the distance travelled by light in a vacuum in 1/299,792,458 of a
second. Do you propose that the definition remains the same as it is today (so the length changes
periodically), or do you propose to change the definition of a metre periodically, so the length
remains fixed? If you want to keep the length of a 1m bar fixed, you would periodically need to
redefine the metre. Today the metre might be defined as the distance travelled by light in a vacuum in
1/299,792,500 and tommorow in 1/299,792,400 of a second, and its anyones guess what it is defined as
the following day.

Or why not just abandon the metre, and use the "SI yard", and define that as the distance between the
nose and the end of the current English monarchs finger? As his or her's (currently her) body shape
changes, then let the "SI yard" change. Is that any less sensible than changing the definition of a
second in the manner you propose?

--
Dr. David Kirkby PhD CEng MIEE,
Senior Research Fellow,
Department of Medical Physics,
Mallet Place Engineering Building,
Gower St,
University College London,
London WC1E 6BT.

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