[LEAPSECS] The Once and Future Time

[Rob Seaman]

On Jan 19, 2014, at 12:31 AM, Clive D.W. Feather <clive at davros.org> wrote:


> Rob Seaman said:

>> Systems, software and civilization depend on both interval time and Earth orientation time.

> 

> In what way does civilization depend on Earth orientation time?


Thanks for acknowledging (through omission) the many dependencies of software and systems on Earth orientation.  Let's see, how about?  The proceedings of the two UTC meetings (http://www.univelt.com/Science.html) were published by the American Astronautical Society because of requirements of spacecraft operations and flight software on retaining the current definition of UTC:

	http://www.cacr.caltech.edu/futureofutc/2011/preprints/28_AAS_11-673_Simpson.pdf
	http://www.cacr.caltech.edu/futureofutc/2011/preprints/30_AAS_11-674_Storz.pdf
	http://www.cacr.caltech.edu/futureofutc/2011/preprints/32_AAS_11-675_Malys.pdf

Need one point out the many ways that civilization now depends on spacecraft?  It's an interesting tell, however, that while my assertion was that civilization and its complex mix of systems (many with software components) depend on *both* Earth orientation time and interval timing (equivalently frequency), that the response is an attempt to divide the argument.

Civil timekeeping - time kept by and for our civilization - depends on both the synodic day and on the SI-second as derived from atomic frequency standards.  UTC as currently defined represents both of these.  The requirement is to maintain the correct functional form; leap seconds are a means to an end.  Seeking to cheat the system requirements and eradicate them will inevitably create more risks and greater expense.


> Given that existing locations have local time several *hours* away from solar time, this seems unlikely.


That said, another answer would be to point to innumerable messages on the lists:

	http://six.pairlist.net/mailman/listinfo/leapsecs
	http://www.ucolick.org/~sla/navyls/

Search on words like "confuses periodic effects with introducing a secular trend".  Static time zone offsets and periodic DST adjustments have nothing to do with the Earth's underlying synodic day.  Apparent solar time is similarly just a charming periodic variation imposed on top of the mean solar clock that represents the unique functional form of the synodic day - on Earth and two dozen other large terrestrial worlds in the solar system (http://futureofutc.org/preprints/files/28_AAS_13-515_Seaman.pdf)

If you are instead making the broader claim that civilization is somehow distinct from its engineering creations, perhaps review the contributions by Paul Gabor and Kevin Birth to the Exton and Charlottesville Colloquia:

	http://futureofutc.org/2011/preprints/
	http://futureofutc.org/preprints/

As well as the resulting discussions and various passages in other contributions.

But it is inherent in any issue of timekeeping precisely that our modern civilization is inextricably tied to its system engineering.  The film Metropolis is in the background as I type this.  One of the first images is of a clock (http://www.mostlypink.net/pics/ma/clocks.jpg).  That the clock face is divided into ten hours suggests that Fritz Lang, at least, believed that reformation of time standards was a possibility ;-)  Of course, the rest of the movie is an argument that we should be careful what we wish for.

"Deep below the Earth's surface lay the workers' city."  Even the worker class, banished to an underworld divorced from the sunlight, have an existence that is dominated by the diurnal cadence of the Earth.  That cadence is the synodic day.  Deviating by even one part in a million from the tempo set by the rotation of the Earth would result in the accumulation of an intercalary leap hour every century.  I suppose the notion is that Metropolis Central Time would just be incremented to compensate - but then one expects that the prime meridian passes through Fredersen's office.  Incremented to what? :-)

However, one suspects you aren't actually questioning the underlying diurnal cadence of our lives.  Civilization depends in vast numbers of ways on the alternation of night and day - to the extent that it is encoded in our biochemistry:

	http://news.harvard.edu/gazette/1999/07.15/bioclock24.html

And the day is not only a unit of time, it was our first unit of measurement of any sort:

	And God called the light Day, and the darkness he called Night.
	And the evening and the morning were the first day.

I'm grateful for the opportunity to pen a defense of the Copernican world view.  The naive ITU proposal is precisely a challenge to something as fundamental as the model of the heliocentric solar system.  This isn't a philosophical issue, it's a question of bad engineering.  The Ptolemaic system would be a poor model to use for navigating spacecraft.

Since 86,400 SI-seconds happen to be within a few milliseconds of the current length of day, some special interests have been emboldened to not only entertain alternate engineering strategies for reconciling interval timepieces (frequency standards) with our synodic clocks - but beyond that to suggest that we can simply forget the whole thing.  Copernicus says otherwise.

The cover of the Charlottesville proceedings is an illustration of a Foucault pendulum with the caption:  "Pendulum motion demonstrates the rotation of the Earth (à la Foucault) and the metering of time independent of Earth's rotation.  UTC and Civil Timekeeping provide both, but will that continue?"  Science reaching at least as far back as Galileo has depended on both kinds of timekeeping - and as Galileo said, eppur si muove...an assertion which can be applied equally to pendulum and Earth.  The SI-second derives from the former.  The days tracked by our calendars from the latter.

Coordinated Universal Time as inherited by the ITU-R expresses both Universal Time (the fundamental synodic day) and Atomic Time (the fundamental cesium frequency standard).  The mandate was to remain reliable stewards of both.

	Mittler zwischen Hirn und Hände muß das Herz sein.

Rob