Re: = t1 - t0 but t0 + i <> t1 when t1 and t2 timestamptz values and i is an interval value - Mailing list pgsql-general

On 2021-03-30 12:36:16 -0700, Adrian Klaver wrote:
> On 3/30/21 10:31 AM, Bryn Llewellyn wrote:
> > > adrian.klaver@aklaver.com wrote:
> > >
> > > The point is horology is cultural, see non-Western calendars and
> > > alternate time keeping methods. Trying to maintain a distinction
> > > between the two concepts only furthers the confusion. The
> > > inconsistencies you see are the result of one(culture) intervening
> > > in the other(horology).
> >
> > I intend the word “horology” to be taken in this sense:
> >
> > « The word "horology" means "the art of making clocks and watches".
> > So the intended meaning of the phrase "horological interval" is
> > "what you'd measure with a clock". The implication is "what you'd
> > measure with the best clock that there is (in other words, a caesium
> > clock) but expressed in seconds and multiples thereof (hours, and
> > minutes, but not days).” »
> >
> > There’s nothing cultural about the size of the caesium unit. It
> > simply emerges from the laws of physics. Maybe you don’t like the
> > word “horology”. I’m open to suggestions for a better term of art.

Most clocks are not atomic clocks. Their job is not to count physical
seconds (or periods of the radiation corresponding to the transition
between the two hyperfine levels of the fundamental unperturbed
ground-state of the caesium-133 atom), but to display "civil time",
which is very much a cultural construct. When I went to bed last
weekend, my clock showed something after 3:00 despite the fact that only
a few minutes before there was a 1 before the colon. That's how a clock
should behave (unfortunately, the clocks in my coffee maker and my stove
don't do that - I have to set the time twice a year).

(Operating systems often have a "wall-clock time clock" and a "monotonic
clock". The wall-clock time clock is expected to mimic a clock on the
wall, including all the cultural baggage like leap seconds, daylight
saving times (although that's usually added in a second layer). The
monotonic clock is supposed to just count seconds at a fixed rate, like
a stop watch.)


> > But I hold fast to the idea that an atomic clock measures time and
> > durations in one way and a calendar measures these in a different
> > way. Seems to me that the whole business of calendars is nicely
> > captured by the term “cultural”.
> >
> > Maybe I could use the terms “atomic clock time” and “calendar time”.
>
> Which are for practical purposes one and the same, otherwise we would not
> have leap seconds as a method of syncing the two.

I disagree. We have leap seconds exactly because they are not the same.
Atomic clock time just counts at at a constant rate - it doesn't care
about the Earth's rotation. People however (well, some people, at least
those who made the rules) do care about that so they add a second every
now and then to keep days in sync with the Earth's rotation (currently
TAI and UTC differ by 37 seconds).

        hp

--
   _  | Peter J. Holzer    | Story must make more sense than reality.
|_|_) |                    |
| |   | hjp@hjp.at         |    -- Charles Stross, "Creative writing
__/   | http://www.hjp.at/ |       challenge!"