[LEAPSECS] drawing the battle lines

[Joseph M Gwinn]

I would propose that ITU is using continuity and uniformity in their
mathematical definitions, implying that the intent is that at least in
definitional theory, UTC be mathematically continuous with all its
derivatives (noise being ignored).  This would exclude step discontinuities
(leap seconds) and piecewise linearity (like UT1).  Given that the length
of a SI second is constant, what's left is a UTC that is a constant offset
from TAI, where the offset changes only if so ordered.

Joe




From:	Warner Losh <imp at bsdimp.com>
To:	Leap Second Discussion List <leapsecs at leapsecond.com>
Date:	03/20/2013 05:35 PM
Subject:	Re: [LEAPSECS] drawing the battle lines
Sent by:	leapsecs-bounces at leapsecond.com




On Mar 20, 2013, at 2:20 PM, Rob Seaman wrote:

>>> 		 2.   a continuous reference time scale corresponds to UTC

without leap second discontinuities;

>

> And also corresponds to UTC with leap seconds.  There are no

discontinuities.

discontinuities here means "irregularity" not the a violation of the
contrived continuity of the variable radix UTC.


>>> 		 3.   the concepts of continuity and uniformity should be

applied strictly in a reference time scale;

>

> This is not a fact, it is a statement of policy and requires detailed

definition.

Viewed from a fixed-radix standard, a leap second is a discontinuity and a
non-uniformity.


>>> 		 4.   the unit for any quantity in metrology is unique, and as

such, a single time scale should also be unique;

>

> Two things.  The SI-second is derived from a more fundamental frequency

standard.  There are and will remain vast numbers of time scales that are
directly or indirectly layered on the SI-second.

>

>>> 		 5.   in the event of a redefinition of any quantity in

metrology, the unit should be invariant, and particularly for the second of
the Système International the respective scale should be continuous and
uniform;

>

> This scale already exists in TAI.  If TAI has issues, it isn't obvious

why UTC needs to be changed.  Does TAI actually have issues?  It is an
opinion, not a fact, to assert that practical time scales need be uniform.
And uniform with respect to what?

TAI isn't disseminated.


>>> 		 6.   the name “Coordinated Universal Time” be maintained in

the case of a redefinition of UTC without leap second adjustments;

>

> This is an opinion, not a fact.  Many disagree with their opinion.





>>> 		 7.   the term “Universal” in “Coordinated Universal Time”

implies that the time scale is to be used throughout the world;

>

> No.  There is no term "Universal" in Coordinated Universal Time.  Rather

UTC parses as Coordinated "Universal Time".  "Universal Time" is a prior
term that has always been approximately equivalent to "Greenwich Mean
Time".  Relying on sophistry in definitions reflects a weak underlying
position.

>

>>> 		 8.   the term “Coordinated” in “Coordinated Universal Time”

implies coordination among National Metrology Institutes and not a
relationship to the direction of the Sun from a position on the surface of
the Earth;

>

> The second half of this sentence belongs with "Universal Time".  Again,

definitions are not facts.

>

>>> 		 9.   the angle UT1 used to relate celestial and terrestrial

reference systems should not be considered as a time scale, but as the
angle that characterizes the variable rotation of the Earth;

>

> UT1 can be both an angle and a time scale.  That the rotation of the

Earth and other bodies varies does not invalidate the identification of the
word "day" with "synodic day".

UT1 is a time realization of an angle. It is an irregular time scale
because it is based on an imperfect oscillator whose frequency error and
time error are not predictable. That's what makes it not a suitable times
scale.


>>> 		 10. the International Earth Rotation and Reference Systems

Service (IERS) provides a means of accessing UT1 in real-time by means of
routinely available predictions of UT1-UTC with precision 100 000 times
better that the coarse approximation UT1 = UTC currently provided by means
of coding UTC to match UT1 within 0.9 second;

>

> This is irrelevant and is meant to imply that any issues with

implementing a redefined UTC will be minor.  They will not be minor for my
community.

If you take the product of inconvenience and probability of that
inconvenience summed over all users, you'll find the change has a low
expected impact.


>>> 		 11.  a wider dissemination of UT1-UTC is to be encouraged;

>

> Again, a policy, not a fact (whether or not desirable).

>

>>> and further recommends

>>>

>>> that the International Committee for Weights and Measures (CIPM) and

the International Telecommunication Union – Radiocommunication Sector
(ITU-R) consider the formation of a joint working group to study the
possibility of coordinating future actions in the definition of the
continuous world-reference time scale.

>

> This may well be a good idea, but perhaps additional institutions should

be involved?

>

> The function of point 9 (in combination with others such at #5) is to

argue that civil timekeeping doesn't need to remain tied to Earth rotation.
Rather, the fact is that time in society depends on both atomic and synodic
time scales.  To control "Universal" "Time" (as opposed to "Universal
Time") they first must argue that a single time scale can rule them all.

>

> It is not obvious why TAI does not already fill this role.  And if not

TAI, define some other continuous time scale (by whatever definition of
"continuous") under a different name, and leave UTC (~ GMT) alone.

TAI is a paper clock. It has no real-time realization. UTC is a real-time
realized clock, and has traceable chains of time transfers.

Warner

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