[LEAPSECS] Consensus building?
scolebourne at joda.org
Wed Feb 2 13:40:43 EST 2011
On 2 February 2011 17:48, Steve Allen <sla at ucolick.org> wrote:
> On Wed 2011-02-02T16:47:22 +0000, Stephen Colebourne hath writ:
>> - the SI-second is a standardised unit of measurement
> which is a conventional construct that is valid in a particular
> reference frame. If I build a perfect cesium chronometer and you
> build a perfect cesium chronometer those will never agree because of
> our differences in relative velocity and depth in the varying
> gravitational potential wells.
> The only way to approach agreement is to apply corrections
> to the chronometer, thus changing it into a clock.
> The nature of the conventions under which the SI second is
> measured and integrated into a time scale have changed
> many times.
That may all be true. But is the SI second a unit of measurement? Is
it standardised? Those are the only two claims made. Do you disagree
with either claim? (You can create new statements and try to get them
agreed of course - your answer suggests that a new statement about
observability/conversion to a clock would be useful)
>> - an SI-based-minute is formed from exactly 60 SI-seconds
>> - an SI-based-hour is formed from exactly 60 SI-based-minutes and thus
>> exactly 3600 SI-seconds
>> - an SI-based-day is formed from exactly 24 SI-based-hours and thus
>> exactly 86400 SI-seconds
> Given that no two observers are in the same reference frame, the
> notion of extending SI seconds into days requires delving into the
> years of discussions on the meaning of relativistic time scales.
If an SI second is a unit, then it must be possible to have a multiple
of that unit. Don't read too much into a single statement!
>> - a solar-day is a measured period of time
> Not in the sense of metrology.
> A mean solar day is a conventional measure of rotation of the
> earth as differenced from a conventional reference point.
> The nature of the measure of the rotation angle and the conventional
> reference point have been changed many times.
> Yes, in the sense of human history and culture.
Is it important enough to have two definitions for those two things?
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