Re: [LEAPSECS] independence day

From: Rob Seaman <seaman_at_noao.edu>
Date: Wed, 5 Jul 2006 01:07:58 -0700

On Jul 4, 2006, at 11:04 PM, Poul-Henning Kamp wrote:

> But yes, likely as not, this is not a black helicopter job, but
> rather sloppy or uninformed text-processing.

One would hope that our helicopter pilots are more skilled in their
maneuvering :-)

Hard to understand how the presence of such verbiage in a funding
bill might be explained by either ignorance or the "oops!" factor,
but I don't think inept political machinations are the major point.
Without belaboring all the discussion over the past seven years, one
might reasonably ask what might best constitute a robust legal
standard for timekeeping - from a systems architecture point of view,
that is.

We've spent a lot of time focusing on precision timekeeping for
technical purposes. I don't think any of us are satisfied with that
discussion, but this has been the primary context - GLONASS, spread
spectrum, navigation, astronomy, etc. But much of U.S. and
international law is concerned with commerce, economics and other
primarily non-technical issues. And unlike folks like us who are
steeped in technical issues, civil timekeepers don't have the luxury
of falling back on some other model of time and rolling their own.

Mean solar time has provided the underlying model of time worldwide
for the past couple of centuries. There are many complications
associated with this - and we've touched on virtually all at one
point or another :-) UTC is one way of conveying an approximation to
mean solar time to a broad audience. I'm not arguing here that UTC
has served this purpose in an ideal sense - but the role it has
filled is as an approximation to an underlying physical reality.

One way to look at the entire leap second debate is as an attempt to
detach legal timekeeping from this physical touchstone (a rather big
touchstone, of course, since it encompasses the entire Earth) and to
connect legal timekeeping to an arbitrary international standard. I
won't make my usual fuss here about retaining the UTC name for a
timescale that would be something quite different from Universal
Time. The point is, however, that nothing - absolutely nothing -
would then protect legal timekeeping in the U.S. or elsewhere from
the whims of future timekeepers at the ITU.

Say we go with leap hours. UTC isn't therefore less malleable than
currently - but rather more so in the only sense that matters for
legal timekeeping. That is, a small entrenched committee would be
able to vote arbitrary changes to international time precisely
because the standard would no longer be tied to any physical
phenomena. One might wonder why changes might be made. I'll only
point out - why not? What in practice would stop these individuals
from leaping the clock forward or backward at will, or from changing
the rate of UTC, or for that matter from making the clocks run
backwards? The IERS has served a sober and professional role of
keeping all our little clocks synchronized to the one big clock. On
the other hand, the very fact of this tedious, tenacious and
tendentious attack on the leap second is to suggest that the ITU has
no such compunction to avoid playing god. The proposal on the table
not only does not specify the procedures and logistics of issuing a
leap hour - it doesn't specify what organization will be responsible
for coordinating the decision, or even how the UTC-UT1 difference
information is to be propagated. It isn't so much a proposal, as a
prohibition against any attempt at carrying on the IERS duties.

Which is to say that the current ITU standard claims to represent the
controlling definition of UTC. I take exception to this, suggesting
rather that the concept of UTC is of broader applicability and that
the ITU has only inherited responsibility for propagating radio time
signals. The very nature of the recent (and one expects tediously
repeated into the future) proposal is to eviscerate the ITU standard
to the extent that the DUT1 information is eliminated from the time
signals. At that point, what precisely is the ITU bringing to the
distribution of time? What of the essence of the original UTC
concept would remain within the ITU bailiwick? What logical or legal
interpretation would continue to assign the responsibility to an
organization that has rejected its entire prior legal basis?

Meanwhile, the Earth keeps spinning and mean solar time continues to
have a coherent expression in the very posture of the planet
herself. What could be more international than relying on the entire
globe as our fundamental time reference? What avoids international
conflict better than a standard nobody can argue with?

If God hadn't created mean solar time, we would have had to invent it.

Rob Seaman
NOAO
Received on Wed Jul 05 2006 - 01:09:12 PDT