[LEAPSECS] Consensus has value

Rob Seaman seaman at noao.edu
Mon Feb 7 21:09:50 EST 2011

Warner Losh wrote:

> Might be a better way to put it. Civilian time users just need to agree on what time it is amongst the various parties. Everything else is a second order effect.

We seem to be debating again, rather than seeking assertions of consensus :-)

"Parties" are not necessarily human. This appears to be the essence of the Chicken Little "The computers are falling!" argument. In particular, parties may sometimes (my position) include "Mother Earth" (or at least, "Mother Nature's sons"). Also, second order effects are not always negligible.

Which is to say that I don't believe we've reached consensus on this phrasing.

> My statement wasn't so much to say that "we can dictate and the civilian users will follow" but rather "once a time convention becomes established, civilian users tend to not worry too much about the details and accept whatever greater authorities tell them the time is." They call the time hotline and/or lookup time via ntp rather than building their own sundial, surveying it and using it to get second-accurate time.

...speaking of second order effects :-) There are numerous issues relating to the ease or difficulty of (initially) instituting this or that policy. These are orthogonal to the long term wisdom of any particular policy.

> The official time is becoming UTC. It used to be UT1, or rather a more strict mean solar time than UTC strictly speaking is (as it is just an approximation of mean solar time).

We'll leave aside the fact that this transition is occurring as a tactic to redefine civil timekeeping :-)

I have no problem with the notion of "approximation". Simply ceasing leap seconds would cause UTC to drift secularly from Universal Time (strict or otherwise) - it would no longer be such an approximation.

>> Whatever it is, I suspect it is on shaky ground historically.


> I don't see how.

You asserted "it used to be UT1". Rather, the definition of UT1 was some complex part of the UTC saga itself. For instance, UT1 is only known after the fact. Civil time "used to be" (substitute your preferred verb here) Greenwich Mean Time.

> I just point out that timezones and DST suggest that a strict, to the second, synchronization with local sun time is unnecessary.

I'll refrain from my usual response that this confuses secular with periodic effects. Mean time is not averaged apparent time, etc and so forth.

UTC is the basis of the common worldwide civil timekeeping system upon which the timezones are layered. UTC is itself layered on TAI. The ITU is seeking to remove a layer from the middle of the cake - and, in effect, claims this won't even disturb the icing ("fondant" for Charm City fans).

> My point here is that "Universal" time is used because it was widely available, not necessarily because of any other intrinsic property of "Universal" time.

Ubiquity is indeed a key requirement.

> It would be unwise to assume that all the characteristics of UT1 are required in any successor.

...and it would be unwise to assume that redefining the meaning of the word "day" is a trivial change.

Avoiding unwarranted assumptions is the point of building consensus before taking action.

> That's why I said above that tweaks to the system that are somehow promulgated or become defacto standards are adopted when they are easy.

This is an excellent argument for change based on evolving the current standard rather than replacing one standard (UTC) with another (TAI) that addresses a different set of requirements. It isn't that change is being considered - the astronomers here have supported the possibility of various (prudent) changes). It is that a dramatic change to the entire dual architecture of (civil) timekeeping is being unilaterally pursued.

> You can see it in UTC even: everybody does the easy parts, many botch leap seconds and hope that ntpd and/or manual intervention will paper-over any mistakes.

Folks on both sides have used these observations to support their positions.

> Some of these changes are minor and matter not at all, while other changes matter a lot (eg, changing the rate that TT ticks by 1e-15 didn't matter, while changing GMT from starting at noon to starting at midnight matter so much that a new name for the new GMT was invented).

The ITU has been free at any point to define a new timescale with a new name.


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