On Wed 2011-02-02T18:40:43 +0000, Stephen Colebourne hath writ: > That may all be true. But is the SI second a unit of measurement?
yes, one that can be reproduced a priori anywhere in the universe that someone has a cesium atom. > Is it standardised? yes. > Those are the only two claims made. But that's not sufficient for use cases. > 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! Multiples of a unit imply the likelihood that people will try to presume linearity. APIs for computing systems present the ability to handle time scales at a precision of 1.e-9 or better, yet spacetime itself is not linear to that level across the span of the earth. Therefore interpretation of the meaning of multiples requires a huge conventional conceptual framework. To get an idea of how large the framework is just for observers on earth see the 179 pages of the IERS Conventions 2010 http://www.iers.org/nn_11216/IERS/EN/Publications/TechnicalNotes/tn36.html and compare those details with previous versions to see the evolution of the conventional conceptual framework. In order to agree on what time it is to that level we have to allow one authority to define that time based on the evolving set of practices and conventions that experts in the field deem best. Not just allow, but as a society recognize the importance of funding their ongoing efforts, and agree upon the utility of their results. This requires consensus, something that has been lacking in the ITU-R process, and fearfully so as seen in the non-consensual forward motion of the proposal detailed here http://www.atnf.csiro.au/iau-comm31/activities.php and also here http://www.bipm.org/cc/CCTF/Allowed/18/CCTF_09-32_noteUTC.pdf wherein it almost seems that Ron Beard has some sort of hypnotic zeal which silences all opposition. > > Yes, in the sense of human history and culture. > > Is it important enough to have two definitions for those two things? That is the active argument in the ITU-R arena. -- Steve Allen <[email protected]> WGS-84 (GPS) UCO/Lick Observatory Natural Sciences II, Room 165 Lat +36.99855 University of California Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m _______________________________________________ LEAPSECS mailing list [email protected] http://six.pairlist.net/mailman/listinfo/leapsecs
