[time-nuts] Re: UTC

Chuck Harris cfharris at erols.com
Wed Jul 27 10:09:21 EDT 2005

```Poul-Henning Kamp wrote:
> In message <42E6C1F7.3040002 at erols.com>, Chuck Harris writes:
>
>>Poul-Henning Kamp wrote:
>>
>>>In message <4A4B4876-7D7F-4D81-AE31-26A757E7AA81 at noao.edu>, Rob Seaman writes:
>
>
>
>>Now, for 3 t-shirts Poul, reread Rob's last paragraph, but this
>
>
> I'm still trying to get the same basic point across, and answering
> his last paragraph would just have repeated the message yet again:
>
> To 99.999% of the Earths population, the Earth is geophysics, not
> timekeeping.
>
> For almost the entire population, time is defined as SI seconds,
> 60 of which is a minute, 24 of which is an hour, 365 of which is a
> year.

That is correct, but you must also remember that 99 and 44/100ths of
the population would do just fine with a timepiece that had no second
hand.  Seconds are just a frill to civil timekeeping.

If you have been watching the population in general, you may have noticed
that there is a decline in the number of people that have any interest in how
things work.  When I was a kid, there wasn't a toy, or appliance that was
safe from my curiosity.  I suspect that you were the same.  Now, with the
exception of sadistic impulses that remove the heads from dolls, kids don't
take their toys apart.  They just want them to work, and when they stop, they
throw them away.

The point being, the needs of the population-at-large is not a valid reason for
making a decision as to whether we need leap seconds, or don't.  The population-
at-large just doesn't care, *at all*.

That puts the decision down to the very few that do care.  Those that care have
already boiled the time situation down to two systems which are each synchronized
to the atomic second, TAI, and UTC.  UTC was designed to be a replacement
for GMT.  For that to be true, it needs to remain synchronized to solar time
at the zero meridian.  That, regardless of how we feel about the implementation,
requires a leap second from time-to-time.

If UTC ceases to remain synchronized to solar time at the zero meridian, then
how does it differ from TAI?  It becomes redundant, and may as well cease to
exist.
>
> There is a well defined formula that streches indefinitely into the
> future, which inserting an extra day almost every fourth year, for
> reasons most people do not claim to fully understand.

They don't need to understand it, they just need someone to tell them
that that is the way it is, and they are happy.  Don't forget, they don't
care about the details of how things work.
>
> I fully agree with Rob that there are prefectly valid physical and
> astronomical reasons for the leapsecond, but I keep trying to tell
> him that like so many other metrological details, the everchanging
> mass of the kilogram prototype comes to mind, it will have to be
> a dirty little secret in the scientfic world:  We cannot economically
> justify imposing leap seconds on the rest of the world with six
> months notice.

Certainly we can.  As I said earlier, 99 and 44/100ths percent of the
population has no need for seconds whatsoever.  The remaining 56/100ths
can slip a leap second in when one is required.  And they can do so
when they get around to it, or not at all, and there will be little or no
consequence.  For those that cannot handle the ambiguity presented
by the leap second, there is TAI.
>
> Leap days are economically feasible because most people have a big
> disconnect between the concepts of timekeeping and calendar but
> mostly because the rule is predictive and can be embedded safely
> in computers which are going to run autonomously for years.
>
> Leap seconds are too small for programmers to have heard about or
> care about, they are unpredictable for more than six months at a
> time and untestable in practice.
>
> Robs position, as I understand it is "fine, fine, fine! just don't
> call it UTC!" and that is not economically feasible either IMO.

I don't believe that is his position.   I believe his position is more
similar to mine, and that is we have defined UTC to be based on
solar time at the prime meridian, the definition has worked adequately
well for those applications that UTC is intended to handle, and there is
no good reason why we need to change the definition at this time.

If an application cannot handle the leap second's ambiguity, then it
really needs to use TAI.

I mean, honestly, if you need 1 second accuracy in your timing, you
need to use a clock that is precise to 1/10th seconds at the very
what happens if he uses a standard that is accurate to the same order
of magnitude as the device he is calibrating.
>
> Leapseconds is not a scientific or astronomical issue, they are
> an economical issue.

No, I don't think so.  The economy doesn't know what a second is.

-Chuck Harris

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