[LEAPSECS] Lets get REAL about time.

Warner Losh imp at bsdimp.com
Mon Jan 23 01:03:27 EST 2012

On Jan 22, 2012, at 11:16 PM, Rob Seaman wrote:

> Warner Losh wrote:


>> So I can't do operations on UTC time stamps that are more than 6 months in the future?


> It depends what operations, and what a timestamp is deemed to mean. Currently UTC approximates UT; it is stationary wrt time-of-day. Myriads of human activities are diurnal and time-of-day is the pertinent timescale. Measuring future or past intervals in SI-seconds is beside the point for these use cases, an exercise in fitting a square peg in a round hole.

UTC is a backward looking timescale. When I say I want something at 10:32:00 am UTC on July 5th, 2013 I want that. I don't want an approximation to UT or anything else. I want that. By converting to a timescale without leap seconds still has the problems of leap seconds.

> The plight will be writ large should the notion of timezone roulette be implemented. In that case, over the centuries it will be similarly unpredictable what timezone a particular country or province, state or city observes - will observe - or did observe at some past moment (without consulting some big book of timekeeping trivia). What is a curiosity currently, the adjustment of a timezone, would become commonplace and historians won't be able to "do operations" on UTC timezone offsets as Zefram noted:

Historically, we'll know. We have the Olson database. In the future we cannot know, because UTC has nothing to do with what time-zone a particular hunk of land will be using in the future. That's a political decision, and always has been. We also don't know what the offset between UT in Basel Germany their town clock was set to on June 18th 1652. There was no UTC then, and I'm not aware of daily records that are extant for such conversions... This doesn't seem to bother most historians. The bigger problem is knowing if Basel was in the Catholic part of Germany or the Protestant to know what date was on the calendars that day (or which day gregorian corresponds to the day that had that date on their calendars).

>>> Other direction. Paris's UT+1h would become TI+1h, then TI+0h, TI-1h, TI-2h, and so on. ("TI" meaning the no-leap-seconds time scale that succeeds UT in common use.)


> Even the direction of drift will be a matter of debate as demonstrated on this list.

Lots of things are debated on this list, but that doesn't mean they are in question... :)


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