[LEAPSECS] Reliability

[M. Warner Losh]

In message: <49646F64.11204.119174AE at dan.tobias.name>
            "Daniel R. Tobias" <dan at tobias.name> writes:

: On 6 Jan 2009 at 10:12, Tony Finch wrote:

: 

: > Note that there's no need for global co-ordination. Each country (or

: > county) can change when it is convenient for them. The effect would

: > probably be a shifting of timezone boundaries in lumps and bumps that

: > averages out to the overall DUT1 drift.

: 

: ...thus ending up with a time zone map even more chaotic and 

: convoluted and ever-changing than the current one, something I 

: wouldn't have thought to be possible.

: 

: And after a few millennia, UTC will actually be a complete day or 

: more removed from the local civil time in any place.  This will be 

: very confusing in places like Wikipedia comment signature datestamps, 

: which use UTC.  (Wikipedia edit histories also use UTC by default, 

: but can be configured by users to display in their preferred time 

: zone.)


Where a few is like 6 or 7.  See
http://www.ucolick.org/~sla/leapsecs/dutc.html for the timelines on
that.  In 5000BC mankind was a collection of hunter gathers that was
just learning how to farm.  The Pyramids of Giza, for example, were
built around 2500BC.  The earliest known hieroglyphics appear around
3200BC in pre-dynastic Egypt.  It has been pointed out that we've also
accelerated the rate of technology, so the next 7k years are going to
see way more development than the last 7k.  I don't think anybody can
make any meaningful predictions out 7k years.  After all, Wikipedia
has only been around 7, so worrying about what it will be like in 7k
years seems a bit premature or presumptuous.


: Also in a few millennia, when the need to alter the Gregorian 

: calendar to correct for alignment with the seasons comes up, that 

: will open the question of whether such calendar alterations apply to 

: UTC, to local time systems, or both.  The keepers of UTC as a strict 

: atomic time standard will undoubtedly oppose any alteration to its 

: calendar rules, but if the local time zones are still officially 

: based on it (even if shifted by an offset of multiple days by then) 

: then it wouldn't make sense to change the calendar rules for them but 

: not UTC, so another big fight on whatever the equivalent of Internet 

: mailing lists is in that era will be anticipated.


The error rate for the Gregorian calendar is like 1 day in 4k years,
so it will take a very long time for enough error to accumulate that
people will want to do something.  There have been proposals to make
years ending in 4000 not be leap years to correct, but nothing
official has happened on this yet.  The Gregorian calendar has a
tolerance of about +/- just over a day, so equinox varies between
20-dec at 20:47UT and 23-dec at 0:18 UT.

Warner