[time-nuts] Re: UTC - A Cautionary Tale
mikes at flatsurface.com
Sun Jul 17 09:37:30 EDT 2005
At 08:25 AM 7/17/2005, obyrne at iol.ie wrote...
>simple arithmetic with a timescale with a variable second would give an order of magnitude better estimate of the amount of time between 2005 Dec 31 23:59:59.9 and 2006 Jan 01 00:00:00.1 than UTC does!
UTC will tell you that there is EXACTLY 1.2 seconds between those two points. No estimation needed, so it would be infinitely better than some loosely defined variable second.
One must understand that UTC does not follow the _convention_ that all minutes have 60 seconds. UTC requires that 59 or 61 second minutes be allowed during leap second events. It also requires one to track when leap seconds occur. There is no ambiguity and no imprecision.
>>However, the idea I like most is to preduct the long term drift over
>>the next 100-500 years. Then, we schedule the leap seconds NOW
>I suspect that mathematicians and computer programmers alike would prefer to use
>quadratic equations than look-up tables, even if the latter are well-defined. Quadratic
>equations are easier to work with than discontinuities.
Neither can be guaranteed to keep UTC in sync to UT1 by the defined amount. There is a very high degree of confidence that leap seconds will accumulate over the long term, but over a shorter term, we may actually need to remove a leap second, as the rotation of the earth seems to be on a current trend of speeding up. http://www.ucolick.org/~sla/leapsecs/dutc.html#atomic.png
There are no discontinuities with UTC, at least not if one uses the mathematical definition of "discontinuity." All time is fully accounted for, and there are no gaps. If one claims that leap seconds make UTC "discontinuous" by some other definition, one must then admit that leap days make most other time scales discontinuous also, for they are logically equivalent, differing only in the amount of time before irregular corrections need to be applied (years for leap seconds/UTC, millenia for leap days/Gregorian).
Nor is UTC entirely unpredictable or random, for we can with some degree of precision (but not exactly), know how much it will differ from TAI at any point in the near future (several millenia). "Irregular" might be a better term to refer to the effect leap seconds have on UTC.
> Also, continuing to use leap
>seconds eventually leads to inserting leap seconds at the end of every month, week,
>then day, though it may take 1,200 years before a leap second is required at the end of
>each month. And, which would the general public prefer - a slightly, imperceptibly,
>varying second that (attempts to) track the earth, or 23:59:60?
23:59:60, since it only occurs infrequently and properly implemented has zero effect on interval measurement. The problem is not how to handle leap seconds, but in getting the infrastructure to actually do so. How many RTC chips handle 23:59:60? Operating systems? Applications? What channels are available to automatically distribute notice of upcoming leap second events? The people/organizations which are complaining about leap seconds have had 33 years to work this out, but haven't for the most part. Now they want to fundamentally change UTC (breaking systems which DO use UTC as intended) to make up for their inaction.
> Finally, over 400 years
>ago, there was a change made to our calendar that is still in use today, and that looks
>like it will still be in use 1,000 years from now (an impressive achievement by our
>forebearers) - I think we should aim for such a long-term solution for the measurement
>of the time of day.
The Gregorian system slips about 1 day every 4000 years. Considering that is shorter than recorded history, and very much less than human existance, I consider that less than "long term."
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