On Nov 17, 2011, at 11:57 AM, Ask Bjørn Hansen wrote:
> I've been following the list for a while and seen many examples of
> communities and significant industries where leap seconds are causing problems
But you've seen no investigations of the significance of the problems, and only
anecdotal evidence that they indeed actually exist.
> (and just stopping them with cause no new friction).
And no evidence whatsoever that redefining UTC will not cause even bigger
problems for these same communities and industries. Nobody has looked. No
Y2K-like inventories have been performed. No tests have been carried out.
> Count me in with the uninformed then and please help inform us.
See presentations at:
http://futureofutc.org/program
The proceedings are just being finished up and should be available in the next
week or so.
> (Just to be clear here; I'm completely serious - I understand the general
> concept of course, but I genuinely don't understand the specific use cases
> for having leap seconds).
System engineering sermon again. Use cases are tools for discovering
engineering requirements. They operate in the problem space. Leap seconds are
a feature of UTC. UTC is the current solution to the problem of civil
timekeeping (or one aspect of the larger solution). The phrase "use cases for
having leap seconds" is not a coherent sentence in systems engineering since
characterizing the problem and proposing and evaluating candidate solutions are
completely different parts of the process.
An engineering requirement for civil timekeeping might be phrased something
like: (A) "human civilization is dependent on diurnal phenomena". (This is
phrased in a rather schematic way to simplify the discussion.) The use cases
that led to discovering this are many and detailed. They would include lots
and lots of diurnal phenomena and more importantly the way human society
depends on them. Asserting that requirement (A) is not actually a requirement
is equivalent to finding ways to undermine the big long list of use cases,
i.e., that trans-Atlantic flights don't follow a daily schedule, that
electrical loads don't exhibit one characteristic 24-hour response in the
Summer and another in the Winter, that rush-hour traffic doesn't rise and fall
one way on week days and another on weekends, etc.
Requirement (A) and other requirements have led to mean solar time being
adopted and maintained as a standard over several centuries. Mean solar time
remains stationary with respect to time-of-day and thus satisfies the diurnal
requirement. Leap seconds have been the price to pay to implement mean solar
time over the past few decades. Other mechanisms are possible - we know this
because mean solar time was successfully implemented before leap seconds.
> Other than telescopes and some related equipment, I have yet to see an
> example of industries or communities that'll have problems with no new leap
> seconds being introduced.
Nobody has looked. The aerospace community seems quite vociferous. Not sure
why the blatantly obvious issues this would cause immediately for astronomers
are not taken as a warning - as a canary in the coal mine. It will be an
interesting experience to fly in a few years as the vast number of systems
internal to the aircraft interact with the vast number of systems on the
ground. Will they all understand that time no longer means time-of-day? Will
they implement corrections in the same direction? Will Airbus and Boeing
behave the same way?
> In my experience the vast panoply of systems is coordinated based on NTP or
> other similar equipment. Most of which does a terrible job handling leap
> seconds.
NTP distributes UTC. That it does not do it perfectly is not the issue.
> Making UTC not have leap seconds would make it more "Universal" in that the
> number of systems telling the same time would go up.
No. "Universal Time" is an atomic concept meaning "mean solar time". One
supposes it might make it more "coordinated", but as with everything else
nobody has actually investigated the details of how well NTP works now versus
how well it would work in the future.
> Can you (or another participant) give me some concrete examples of stuff that
> needs leap seconds and don't already have well established mechanisms for
> adjusting the time output from their GPS or other time keeping equipment
> appropriately?
See
http://www.cacr.caltech.edu/futureofutc/program/presentations/AAS_11-674_Storz.pptx.pdf
Even very very high tech equipment has been implemented under the quite
reasonable assumption that "Coordinated Universal Time" is a kind of "Universal
Time", meaning (as it always has) mean solar time.
Rob
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