18 Nov 2022 - The fate of the leap second may be decided today at Versailles

[gary]

The International Bureau of Weights and Measures (BIPM – Le Bureau Internationale Poid et Mesure) meets today, November 18 2022, in Versailles, to vote on Resolution D, which may determine the fate of the "leap second".

The world has several standard time references and a set of standards as to how they relate to each other. The major ones are :-

TAI - is kept by atomic clocks.

UT1 - based on the Earth's rotation wrt a reference frame pegged to the positions of quasars typically billions of light years away.

UTC - a synthetic time standard which is based on TAI but kept within 0.6 seconds of UT1 by inserting or removing leap seconds now and then as the Earth rotation slows down or speeds up. Originated in 1972, currently TAI − UTC = 37 seconds.

If leap seconds are abandoned, slowly over the centuries what time the sun and stars appear to rise and set with respect the civil time shown on your watch (or phone, etc), will change in part as a function of that TAI - UTC difference.

Depending on what is decided - or not - in France today, we might, for example, see a resolution that adopts a new time standard called International Time (TI) that replaces the current UTC standard (which is used to determine your local time according to your time zone) and which may be locked to TAI and no longer be adjusted for Earth rotation.

[Peter Ward]

Clocks no longer in sync with the earth's rotation?
Bah! Humbug I say!

Reminds me of this old gag.

A physicist is walking down the street, and sees a sign in a shop front that reads "Watch repairs done here". Needing his watch serviced, he goes in and is greeted by a fellow in the front office who he asks whether he can repair his watch.
The fellow replies, "Oh heavens no, we don't do that sort of thing here".
Puzzled, the Physicist points out the sign in the window.

"The sign? You need to understand , we are all mathematicians here....we just make signs...."

[Steffen]

Originally Posted by gary

Depending on what is decided - or not - in France today, we might, for example, see a resolution that adopts a new time standard called International Time (TI) that replaces the current UTC standard (which is used to determine your local time according to your time zone) and which may be locked to TAI and no longer be adjusted for Earth rotation.

I wonder what the benefit of that would be. Synthetic time (or calendar) references, including the leap seconds and leap years they bring along, are easily handled by computers and don’t seem to be causing any issues. Abandoning them would cause the sun to be high in the sky at midnight in the distant future.

[gary]

Originally Posted by Steffen

I wonder what the benefit of that would be. Synthetic time (or calendar) references, including the leap seconds and leap years they bring along, are easily handled by computers and don’t seem to be causing any issues. Abandoning them would cause the sun to be high in the sky at midnight in the distant future.

Hi Steffen,

You would hope that all software practitioners would get this right.
However, recent history is littered with examples of system failures as a result of leap seconds and the software not handling it correctly.

One of the more well publicized examples was the Amadeus airline reservation system which went down for more than two hours in 2012.
Amadeus was handling up to 3 million bookings and 1 billion transactions per day at the time. When it crashed, it caused more than 400 Qantas flights to be delayed.

https://www.theguardian.com/technolo...-qantas-reddit

[multiweb (Marc)]

I had no idea time keeping was so involved. Thanks for sharing Gary

[gary]

As an update :-

Originally Posted by Elizabeth Gibney, Nature, 18 November 2022

The practice of adding ‘leap seconds’ to official clocks to keep them in sync with Earth’s rotation will be put on hold from 2035, the world’s foremost metrology body has decided.

The decision was made by representatives from governments worldwide at the General Conference on Weights and Measures (CGPM) outside Paris on 18 November. It means that from 2035, or possibly earlier, astronomical time (known as UT1) will be allowed to diverge by more than one second from coordinated universal time (UTC), which is based on the steady tick of atomic clocks. Since 1972, whenever the two time systems have drifted apart by more than 0.9 seconds, a leap second has been added.

...

The CGPM — which also oversees the international system of units (SI) — has proposed that no leap second should be added for at least a century, allowing UT1 and UTC to slide out of sync by about 1 minute. But it plans to consult with other international organizations and decide by 2026 on what upper limit, if any, to put on how much they be allowed to diverge.

...

Representatives from Canada, the United States and France were among those at the CGPM who called for the leap second to be scrapped before 2035. But Russia, which voted against the proposal, wants to push it back to 2040 or later to deal with technical issues within its satellite-navigation system, GLONASS.

The Russian system incorporates leap seconds, while the Global Position System (GPS) and others already effectively ignore them. The decision means that Russia might need to install new satellites and ground stations, says Felicitas Arias, former director of the Time Department at the International Bureau of Weights and Measures (BIPM) in Sèvres, France.

Astronomers who rely on UT1 to align their telescopes will also need to adjust, says Elizabeth Donley, who leads the Time and Frequency division at the National Institute of Standards and Technology, in Boulder, Colorado. But the current situation is unsustainable and would continue to get worse, she adds. Different organisations handle the leap second differently (Google, for example, smears out the extra second in the 24 hours around midnight UTC). This creates an ambiguity between time sources of as much as half a second, she says, “which is huge.”

Although in the long term Earth’s rotation slows due to the pull of the Moon, a speed-up since 2020 has also made the issue more pressing, because for the first time, a leap second might need to be removed, rather than added. UTC has only ever had to slow a beat to wait for Earth, not skip ahead to catch up with it. “It's kind of being described as a Y2K issue, because it's just something that we've never had to deal with,” Donley says.

There is a chance that the International Telecommunications Union (ITU) could stymie plans to make the switch in 2035. The body effectively ceded decision making about the leap second to the CGPM in 2015, and Arias says its working group agreed with the CGPM’s proposal. But the ITU remains in control of disseminating UTC, and could argue that the time is not right to make the change, she says. “This is the thing that makes us a little bit nervous.”

Although human timepieces have been calibrated with Earth’s rotation for millennia, most people will feel little effect from the loss of the leap second. “In most countries, there is a one hour step between summertime and winter time,” says Arias. “It is much more than one second, but it doesn't affect you.”

Future metrologists might find more elegant ways than the leap second to realign UTC and UT1. At the point where the difference becomes significant, “our ability to reconcile it will be better than what our ability is right now”, says Macdonald.

Or they might not bother, Arias adds. When the difference becomes big enough, countries could permanently shift their legal time zone by one hour, she says. Or we could even decouple our sense of time from the Sun entirely, to create a single world time zone in which different countries see the Sun overhead at different times of day or night. “It could be a solution,” she says. “Science already doesn’t use local times, we talk in UTC.”

Story here :-
https://www.nature.com/articles/d41586-022-03783-5

With the declaration to stop inserting or removing leap seconds from 2035
or earlier, in essence the problem of the divergence of UTC from UT1 has
been put off to the future to deal with.

It's not the first time in the world's history that a disruption in timekeeping
standards has caused chaos.

Consider the month September 1752 :-

  September 1752     
Su Mo Tu We Th Fr Sa  
       1  2 14 15 16  
17 18 19 20 21 22 23  
24 25 26 27 28 29 30

The nearly two weeks missing between the 2nd and 14th were of course because of the switchover to the Gregorian calendar.

Some called out, "Give us back our two weeks". Workers demanded to be paid for the missing days and landlords demanded rent for them.