[time-nuts] Re: UTC - A Cautionary Tale

Rob Seaman seaman at noao.edu
Fri Jul 15 17:57:14 EDT 2005

Poul-Henning Kamp replies:

>> Shouldn't we explore the requirements and use cases before making  
>> a change to the standard?

> Absolutely, but shouldn't we look at more than astronomy while  
> doing so?

Are you under the impression that the folks pushing this proposal are  
looking anywhere beyond their own perceived self-interest?  Look at  
http://www.ucolick.org/~sla/leapsecs for examples of legal issues.  A  
reporter from the WSJ has been calling around for a planned front  
page story about leap seconds.  I don't know how it will be  
positioned, but they are surely interested in this from a commercial  
point of view.  Historians may care deeply about whether some event  
occurred on one day (as defined by the Earth) as opposed to another  
day (as defined by mid-level international bureaucrats).  Religious  
issues anybody?

> I will agree with you that the current process for decision is  
> somewhat flawed seen from a democratic point of view

It is flawed from the point of view of reaching a viable and  
logically self-consistent solution to the problem.  The Earth spins.   
We should take note of that fact in all sorts of decision making.

> The matter of the fact is that we have four groups of people here:

No, we actually have dozens or hundreds or thousands of groups.  No  
attempt has been made to reach most of them.

> Only Group 1) wants leapseconds because they are used to having them.

Astronomers want access to time-of-day (UT) as well as interval time  
(TAI) - UTC uniquely provides information about both.  I would  
strongly prefer that civil time continue to track time-of-day.  If  
the folks who claim to have authority over this decision (good luck  
with that at the end of the day) want to divorce civil time from the  
spinning Earth, well that is one thing.  But to continue to call the  
resulting time scale "UTC" is an deeply troubling abomination.  Not  
only would this scheme sacrifice time-of-day, it also fails to  
capture atomic time since it will just leave 34 seconds dangling for  
all eternity.

A far more coherent proposal would be to simply switch civil time  
from time-of-day to atomic time.  This would recover the 33 (soon 34)  
second "gap" and that gap would be a useful tool to impress the -  
well - civilians that a significant change is being made to their  
civil clocks.

Astronomers could then continue doing what they've done for hundreds  
of years and set their own clocks.

Personally, I think this is silly - but at least it is self- 
consistent.  The proposal on the table is not only silly - it is  
inconsistent and naive.

> Just carrying out the "Y2K-like inventory" will cost more money  
> than the astronomers would ever dream of getting their hands on.

You do, perhaps, understand that astronomers had some pretty  
stringent Y2K remediation of their own.  I was attempting to make the  
point of the true underlying scale of this issue.  Supporters of this  
proposal are simply *assuming* that a diverging DUT1 will cause no  
life-threatening issues.  We were lucky with Y2K because we invested  
in creating our own good luck.  Nobody has invested ten cents in a  
good luck safety net toward the retirement of leap seconds.

> The problem is that UTC is printed in too many documents.  The cost  
> of having para-legals track it all down and passing ammendments to  
> change it all to TAI or whatever we decide to call it would cost a  
> fortune you cannot even dream about.

The fact is that UTC is used interchangeably with GMT throughout many  
of those documents.  The concept of "leap seconds" is interchangeable  
with the concept of "Greenwich mean time".  UTC is not just an empty  
bureaucratic name for "civil time".  The equivalence of GMT and UTC  
is not something that can simply be wished away.

> And you think the rest of the world think your clocks is a good  
> enough argument that we have to pay the bill for down time, extra  
> man-power and all that stuff ?

It isn't astronomers who need protection here.  Anybody participating  
in the discussion from any community is technologically astute enough  
to sort out the issues.  All we will need is money to restore  
services like telescope control to the level they were at before such  
a change.  A colossal waste of time and money, but we'll muddle  
through no matter how stupid a decision is made.

The public - including folks like applications programmers who aren't  
educated in such issues - rely on many systems of time implicitly.   
They rely on both interval time and time-of-day; they also happen to  
often confuse the two.  I don't know (yet) what will break.  There  
has simply been no work whatsoever invested in resolving this  
question.  Most communities (including an ATC technician I talked to  
a couple of years ago) have been left completely out of the loop.

As many things are likely to break because of failing to issue leap  
seconds as are likely to break because of continuing to issue them.   
The difference is that the former will break in ways that are harder  
to diagnose and fix because they will represent deep seated failures  
of the conceptual model of time.

The kinds of things that break when a leap second occur, on the other  
hand, represent failures of engineers, programmers and managers to  
properly implement a self-consistent conceptual model that has been  
in place as an international standard for three decades.

For many purposes the concept of time can be as sloppy as you want.   
Are these the purposes for which this list exists?

Rob Seaman

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