> ... the "invisible infrastructure" of the web; balancing historical accuracy with the technical need to minimize zone fragmentation is a much more complex trade-off than it appears on the surface ...
The complexity goes up tremendously if some condition is rarely encountered: eg leap second. This means it gets pushed to a "corner case" and tested more lightly and more rarely.
At $work around 2014 we had three different hardware GPS types which we used for precision timekeeping; some chips, daughterboards, and firmware. One day a leap second arrived -- it gets broadcast to aGPS hardware a day ahead of time -- and all three implementations handled it differently. One handled it, one did something else like ignore it, and I think one even bricked itself. That situation was less than bueno.
Where I live, high noon today occurs at 1:03 PM. No one is complaining that it is 3 minutes (or 63 minutes) off. It's a non-issue for 99.9% of the population.
* https://www.npr.org/2024/03/30/1241674216/climate-change-tim...
† T23:59:58Z would have skipped/suppressed :59 and gone to T00:00:00Z.
That said, no one wants to admit it, so contemporary science follows Falsification, where we find ways to not actually make claims about reality. (Which as an Instrumentalist/pragmatist, I love Karl Popper, its just not metaphysical truth. And that would break Popper's heart)
There is some talk of eliminating the leap second, which would over time have the Earth and sun diverge with regards to noon and such. One 'answer' to this concern is to have a 'leap hour' or something in the future (some future generation's problem, not ours): but given that people can't even get February 29th correct now, and it happens regularly, I don't see how a one-off event would be made to work. It'd be a huge coördination problem.
Just look at the introduction of the Gregorian calendar: it was slightly off since the time of Julius Caesar, but that minor error added up over time, to the point that to get the equinoxes/solstices back to where they 'should' be 10 days had to be removed with the Gregorian calendar. And because of politics (or a religious flavour) it took a long while for everyone to get on the same page.
But I do think there is a valid argument that the infrequency of these events cause more issues than maybe one large adjustment 500 years from now would cause. Not sure where I land on this one.
I'd argue the opposite is true for anyone who has studied statistics which is largely built on Instrumentalism (think George Box: 'All models are wrong, but some are useful') and Popperian falsification (Null Hypothesis testing). We are absolutely taught to treat models as predictive tools rather than metaphysical truths.
The leap seconds were an attempt to have wall clock time map to the planet's rotational angle consistently despite the problem that the planet's spin varies unpredictably.
Yes the "leap hour" is a legal fiction of course. In reality in the event anybody cares about this in the distant future they will make the kind of "drastic" changes you've probably experienced twice a year for your whole life and barely noticed... More likely because the drift is so incredibly slow they won't change anything.
I had to look it up: https://www.timeanddate.com/time/negative-leap-second.html . In proper words, the clock ("the one humanity agrees to use) would skip 23:59:59Z.
I wonder how much chaos a minute that only has 59 seconds would cause. Measurements would be off by that missing second (e.g. a pipeline delivering fuel at 60 liters/minute would surprisingly only have 59 liters in that minute..).
Thanks for making me a decade younger :)
At the beginning of january and july, observe the difference between UT1 and UTC. If the difference is >= 0.6s, a leap second will be inserted at the end of june/december. Publish the results here: https://hpiers.obspm.fr/eoppc/bul/bulc
“Over time” really glosses over how much time it would take. In 500 years there might be half as much divergence between solar noon and 12:00pm as we intentionally inflict on ourselves with DST, or that France and Spain inflicted on themselves in the 1940’s so they could share a time zone with Germany. By the time anyone will even notice we will probably change time systems for other reasons anyway. It’s not even remotely comparable to the Julian/Gregorian issue, which dealt with leap days. Each day has 86400 seconds.
<rant> It won't happen on a human scale. So why oh why do we screw around with this moronic leap-second nonsense ? Oh dear, in the year 4000 noon will arrive three minutes earlier compared to now. So? </rant>
Compare that to removing the leap day, where the start of seasons would be noticeably affected within just a few decades. Hundreds of years ago, a pretty insignificant headache was invented which is providing constant payoffs.
* https://www.scientificamerican.com/article/leap-seconds-may-...
* https://scripps.ucsd.edu/news/global-warming-influencing-glo...
The general trend is slowing down. Apparently (?) once the day gets to be 24h+0.001sec (+1 millisecond), a leap second would occur about every 1000 days; then when it becomes 24h+0.002sec, a leap second would occur about every 500 days; when it reaches 24h+0.003sec, a leap second would occur about every year; etc.
And taking fluid dynamics, we used renyolds number, which is a made up ratio that helps for decision making... Its not like when we answered questions, we could answer the grey area we are discussing.
If I had to guess, I think its due to western civilization being built of Platonism (and even Aristotle was infected). Our science and morality is later built by platonic realism. Only in the last 100-ish years are we starting to get over it.
I think it matters. No the planets are not doing circles around the sun. Circles don't actually exist, they are doing elipses.
Also 'real' has quite a few meanings. If I ask the question 'Are you closer to a keyboard or the gym?' does that question exist?
This kind of stuff does end up mattering. It becomes much more noticeable in psychology (and biology). If you read Freud, Adler, or Jung, you will say 'Oh extrovert! I've seen that before!' But then you realize its vague and almost always true. Its like a horoscope.
So if we think there is a truth to reality, we look for perfect relations. If we think its impossible for humans to figure out, we look for best fits.
For 99% of the world today, high noon =/= 12:00:00. Nothing breaks because of this. The world continues to run.
The FreeBSD folks test(ed?) their code for these things and it works:
* https://lists.freebsd.org/pipermail/freebsd-stable/2020-Nove...
Of course third-party userland code understanding what happens is another thing.
And anyone that cares about the relationship of the time of day and the position of the Sun.
Granted, it's not a lot, only a minute per century.
The last leap-second I encountered (also the 2014 one) crashed my MySQL databases.
you wouldn't assume that it depends on time like that, because honestly why would it? "surely it's fine, NTP corrects drift of a second fairly frequently"- but a leap second is not a drift, it's something quite insane unless your primitives are solid. Nobody would test for this.
Leap hour replaces all of that with what is more or less equivalent to a change in DST rules (except for more time zones at once). DST changes don't go perfect either by any means... but we do them regularly enough without the world crashing down that doing an additional shift change of an extra hour every 5000 years is almost certainly less hassle and breakage than the leap second approach breaking things every ~2 years.
Statistically, nobody on Earth knows what UTC is. People know about their local time zone and how it related to time zones in other countries. Where the position of the sun is relative to UTC, almost nobody knows.
I wonder if all NTP implementations don't follow those guarantees?
Oh and another app that hates clock jumps used to be sshd; it would just bail out and drop all connections. We found that out while chasing ANOTHER bug in SunOS on a T4: they didn't have it mutexed right so it possible to read its RTC register while it was in the middle of getting updated so the client would read a garbage time. We chased NTP for a week before realizing it was the kernel.
There was a resolution in 2022 to make a decision in or before 2035, to increase the allowable deviation from one second to a longer interval, like one minute. But that would become more frequent in the long run as well, and likely would still cause disruptions whenever it happens. Though on the other hand there would likely be a longer advance notice for it as well.
How can people manage with noon off by minutes, yet want leap-second accuracy every 6 months?
Is that true? Per Wikipedia:
> Since [1972], 27 leap seconds have been added to UTC, with the most recent occurring on December 31, 2016. All have so far been positive leap seconds, adding a second to a UTC day; while a negative leap second is theoretically possible, it has not yet occurred.
Either way, it's due in part to Earth's rotation slowing down, so the average drift would still be non-zero.
Prescheduled.
Now tell everyone we're having one June 30, 2029, and see how things go.
No leap second 2026-06-30, per below. See attached patch. -- Tim Parenti ---------- Forwarded message --------- From: IERS EOP Product Center iers.eoppc@obspm.fr Date: Tue, 6 Jan 2026 at 06:50 Subject: Bulletin C number 71 To: bulc.iers@obspm.fr INTERNATIONAL EARTH ROTATION AND REFERENCE SYSTEMS SERVICE (IERS) SERVICE INTERNATIONAL DE LA ROTATION TERRESTRE ET DES SYSTEMES DE REFERENCE SERVICE DE LA ROTATION TERRESTRE DE L'IERS OBSERVATOIRE DE PARIS 61, Av. de l'Observatoire 75014 PARIS (France) Tel. : +33 1 40 51 23 35 e-mail : services.iers@obspm.fr http://hpiers.obspm.fr/eop-pc Paris, 06 January 2026 Bulletin C 71 To authorities responsible for the measurement and distribution of time INFORMATION ON UTC - TAI NO leap second will be introduced at the end of June 2026. The difference between Coordinated Universal Time UTC and the International Atomic Time TAI is : from 2017 January 1, 0h UTC, until further notice : UTC-TAI = -37 s Leap seconds can be introduced in UTC at the end of the months of December or June, depending on the evolution of UT1-TAI. Bulletin C is mailed every six months, either to announce a time step in UTC, or to confirm that there will be no time step at the next possible date. Christian BIZOUARD Director Earth Orientation Center of IERS Observatoire de Paris, France
But yes, point taken.
The counterpoint is that it costs little.
The time period of the Earth fluctuates a lot [0] and actually in 2020 it was less than 24 hours, but not a large enough change to warrant a negative leap second. If you go back to the 1940s, we would had needed negative leap seconds if we had leap seconds at all then, and going back 150 years we would have needed multiple negative leap seconds every year for several consecutive years.
What we can say is that on average, it is close enough to 24 hours and the average over hundreds of years is even closer to 24 hours that it's not worth adding these extra seconds as you'd then need to remove them again later on.
[0] https://c.tadst.com/gfx/900x506/graphlength-of-day.png from https://www.timeanddate.com/time/negative-leap-second.html
Radical changes to time-related software cost little ? Stop press !
Which is about how long it took for folks to switch from the Julian to the Gregorian calendar.
I haven't once done a single software upgrade related to leap seconds.