[time-nuts] FW: Bulletin C number 30

Magnus Danielson cfmd at bredband.net
Mon Jul 4 15:21:18 EDT 2005

From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
Subject: Re: [time-nuts] FW: Bulletin C number 30 
Date: Mon, 04 Jul 2005 21:02:35 +0200
Message-ID: <31556.1120503755 at phk.freebsd.dk>

> In message <20050704.204026.56945047.cfmd at bredband.net>, Magnus Danielson write
> s:
> >> >> It also means that the attempt to prevent leapseconds before they
> >> >> do more damage failed...
> >> >
> >> >Would the alternative be much better?
> >> 
> >> Lets not restart that discussion :-)
> >
> >I kindly asked for your opinion. I know there have been debates on this, but I
> >haven't followed them and whatever solutions I have seen all have downsides
> >that I don't think is an improvement. In the end, I think this might be a
> >bicycle-stand discussion in which there is no real right answer, we just need
> >to select one of them and stick with it for better or worse.
> My opinion was rather forth and back, until I read (yet another) article
> about colonizing Mars.
> It just doesn't make any sense for an astronaut on Mars to adjust
> leap-seconds.
> And btw, it probably would not even be a leap-second for him, since
> general relativity would take its toll.  I'm not sure my grasp of the
> math is good enough to figure out how long his leap-second would be.
> Instead, if we abandon leap-seconds, then we finally have a _truly_
> universal timescale.
> It will not be locked to any more or less random piece of geophysics,
> anyone with a cesium clock and a set of gen-rel coordinates will be
> able to figure out what time it is, and time intervals can be measured
> and compared without weird gottchas.

No. You are missing a detailed refinement in the definition of a second, it is
assumed that the Cesium clock is at sea-level. The reason being that due to
Einsteins relativistic theory, the gravity potential will also pull the speed
of the clock, and this have indeed been verified with Cesium clocks. For
instance, the GPS satellites have their clocks set slightly low before launch,
since when they reach orbit their frequency as we view it will be different.
So in this context the leap-second doesn't really add much trouble. It is
already adapted to the world we live in and matches many sigmas of our needs.

Also, the Cesium atoms is assumed to be at 0K, so anything but that is an

> Yet it would still be a good enough approximation for the 99% of
> the population to not notice any difference for the next half
> millenium and if we find out we want to keep the sun "near south
> at noon" we can jump timezones to do so with 100 years of advance
> notice.

Considering how time-zones is set, I start to wonder. Look at the time zones
in South America and you see what I mean.

> The other half is that leap-seconds are just not testable in a computer
> setting, and therefore I am sure that any cost of dropping them will
> be totally offset by the savings in the IT industry.

I am not even sure that the IT industry is really spending a whole lot on this
issue. Most of them is to the best of my knowledge fairly ignorant to this
among other problems. Just having charging systems track UTC through NTP would
be a huge step forward IMHO.


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