If I was designing a protocol from scratch that required accurate time, I
would indeed use TAI. In fact I am planning to do exactly that.
The problem here is fear of the unknown. A small clique that has a very
narrow set of interests (and not ones I find very important) has by
tradition and inertia been left to decide this issue according to what
suits them. Proposing to introduce a third scheme and even more confusion
is a bad technical strategy but possibly an effective political strategy.
It is like threatening civil disobedience, once someone decides that they
care enough to risk breaking the system it becomes much harder to defend
the status quo.
I agree with Brian's points about the fact that time is an arbitrary
quantity. One relativity is considered, time becomes a mindbendlingly
complex notion. The poles are moving at a different speed relative to the
equator for a start. And the orbit of the earth is chaotic. Oh the fun
people can have if they want to try to issue correction factors.
Add to that the fact that the prime meridian is located on a tectonic plate
that is essentially floating on a sea of molten magma.
Let time be time and let people who want to tie physical phenomena to time
work out the relevant correction factors.
On Fri, Jan 20, 2012 at 10:32 AM, Marshall Eubanks <
marshall(_dot_)eubanks(_at_)gmail(_dot_)com> wrote:
On Fri, Jan 20, 2012 at 10:13 AM, Tony Finch <dot(_at_)dotat(_dot_)at> wrote:
Nick Hilliard <nick(_at_)inex(_dot_)ie> wrote:
Your arguments in favour of abolishing leap seconds are all good. But
can
you please do us all a favour and provide a similarly lucid list of
reasons
that an apologist would use to say that leap seconds should be kept.
I agree that leap seconds are a horrible bodge that would be best got rid
of. The reasons to keep them mainly revolve around systems that require
UT1, i.e. the angle of rotation of the Earth, and the protocols that
disseminate UT1.
These include:
Astronomical systems
Space and satellite ground stations
Time broadcast standards
All of these are computer controlled now-a-days, and have been for
some time. Even in the 1980's, the computer systems used
UT1, not UTC.
Many protocols and software implementations rely on the guarantee that
DUT1 (the difference between UTC and UT1) is less than 0.9s. For instance
many time broadcast formats don't have space for larger values of DUT1.
Many instruments that point at the sky rely on the fact that DUT1 <
0.9s for establishing an initial rough aim.
Not so much the professional ones.
For more examples see http://futureofutc.org/preprints
Look at Daniel Gambis' survey
Preprint-668
(~ 75% in favor of not changing anything).
At a more philosophical level a lot of people find it difficult to accept
the idea of decoupling time from Earth rotation, to the extent that they
say it is obvious nonsense or foolishness, even though the rate error is
only one second every year or two. However UT1 is slowing down
quadratically, so the time scales will diverge increasingly rapidly.
Yes. Note that for the same reason leap seconds will, in a century or so,
start
to come very frequently.
We can paper over this difference by adjusting time zones every few
hundred years. In fact time zone adjustments will work further into the
future than leap seconds. But speculating about what will happen that far
into the future is foolish.
Numbers for divergence between UTC and TAI:
http://www.ucolick.org/~sla/leapsecs/dutc.html#dutctable
My actual proposal, if I were to make one, would be to keep UTC, but
to make TAI "Internet time" and try and
move most electronic things to TAI, keeping UTC only for civil time.
Note that time is tricky and slippery and _any_ change, even this one,
will have some painful consequences, for somebody, and past
experience is that some of those won't be found until the change is made.
Regards
Marshall
Tony.
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