On 2015-01-26, William Unruh <[email protected]> wrote: > On 2015-01-26, Jochen Bern <[email protected]> wrote: >> On 01/23/2015 08:03 PM, [email protected] wrote: >>> The US will soon be considering a means for dissemination of delta T via NTP >> >> Does that read "there's *several* teams working on NTPv5 and not >> communicating with each other right now" ... ? >> >>> The ITU has just met in Geneva and discussed the future of leap seconds. >>> The US is in favor of dropping them, the Brits are in favor of keeping >>> the tradition of leap seconds, [...] >> >> Leap seconds are an artefact of a) rotation of Earth (which is ever >> slowing down because of mechanisms that nothing short of pointing a >> giant disintegrator ray at the Moon can stop, on top of the uncertainty >> reflected in the unpredictability of current leap seconds), b) the >> precision we have achieved in measuring - supposedly immutable - >> physical time, and c) a desire to have time represented in a way that >> alludes to the traditional "apparent position of the Sun right where I >> stand (on the surface of the Earth)" notion. You can quantize and/or >> distribute "leap seconds" in a different way, but you can NOT "drop >> them" short of kissing one of these three basics goodbye. > > No. It arises from the fact that the second is defined according to a > physical principle ( the frequency of oscillation of a cesium atom in a > certain transition) and the rotation of the earth. It used to be defined ^not > by the rotation of the earth (which was the best clock available) 86400 > seconds in a mean solar day. But as you say, defined in terms of the > oscillations of that transition, the length of the day can vary-- both > because of the moon and because of things like earthquakes and global > warming. Were we to define the mean solar day as 86400 sec, then it > would always be 86400 sec. But theory says that that would make the > behaviour of may other systems much more difficult to describe. > > >> >> (If you read through the comments ITU received along with the votes when >> they put up the poll, you will notice that a great many "abolish leap >> seconds" voters proposed schemes that actually do *not* *abolish* the >> concept of leaps but merely distribute the corrections differently, from >> infinitesimal leaps to the exceedingly rare leap minute.) >> >> Regards, >> J. Bern
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