4 ms·

> There’s an ongoing effort to end leap seconds, hopefully by 2035. I don't really like this plan. The entire point of UTC is to be some integer number of sec

> There’s an ongoing effort to end leap seconds, hopefully by 2035. I don't really like this plan. The entire point of UTC is to be some integer number of seconds away from TAI to approximate mean solar time (MST). If we no longer want to track MST, then we should just switch to TAI. Having UTC drift away from MST leaves it in a bastardized state where it still has historical leap seconds that need to be accounted for, but those leap seconds no longer serve any purpose.

phicoh 2y ago
The is no such thing as TAI. TAI is what you get if you start with UTC and then subtract the number of leap seconds you care about. TAI is not maintained as some sort of separate standard quantity. In most (all?) countries, civil time is based on UTC. Nobody is going to set all clocks in the world backwards by about half a minute because it is somewhat more pure. GPS time also has an offset compared to TAI. Nobody care a bout that. Just like nobody really cares about the Unix epoch. As long as results are consistent.
- gerdesj 2y ago
  The only think we can be certain of is that the Summer Solstice occurs when the mid summer sun shines through a trillithon at Stonehenge and strikes a certain point. From there we can work outwards. The logical thing to do is to precisely model Stonehenge to the last micron in space. That will take a bit of work involving the various sea levels and so on. So on will include the thermal expansion of granite and the traffic density on the A303 and whether the Solstice is a bank holiday. Oh bollocks ... mass. That standard kilo thing - is it sorted out yet? Those cars and lorries are going to need constant observation - we'll need a sort of dynamic weigh bridge that works at 60mph. If we slap it in the road just after (going west) the speed cameras should keep the measurements within parameters. If we apply now, we should be able to get Highways to change the middle of the road markings from double dashed to a double solid line and then we can simplify a few variables. ... more daft stuff ... Right, we've got this. We now have a standard place and point in time to define place and time from. No we don't and we never will. There is no absolute when it comes to time, place or mass. What we do have is requirements for standards and a point to measure from. Those points to measure from have differing requirements, depending on who who you are and what you are doing. I suggest we treat time as we do sea level, with a few special versions that people can use without having to worry about silliness. Provided I can work out when to plant my wheat crop and read log files with sub micro second precision for correlation, I'll be happy. My launches to the moon will need a little more funkiness ...
  - ForOldHack 2y ago
    Sorry to say Stonehenge or the plate on which is stands is moving... to the east, but the wobble of the earth is changing.
    - gerdesj 2y ago
      Isn't the Eurasian plate moving widdershins? The Wiltshire Downs and Salisbury Plain is mostly chalk/limestone. That is a porous rock which will expand and contract on water ingress/egress and be affected by atmospheric humidity. I've no real idea but I suspect that Stonehenge will rise and fall vertically(ish) on a seasonal and other longer rhythms.
      - ForOldHack 2y ago
        Widdershins: "in a direction contrary to the sun's course.." Interesting. The Eurasian plate is moving east, which is widdershins to the longitude, but not the latitude. ( Note: I am a Scot, and added widdershins to my dictionary. )
- LegionMammal978 2y ago
  > The is no such thing as TAI. TAI is what you get if you start with UTC and then subtract the number of leap seconds you care about. TAI is not maintained as some sort of separate standard quantity. There is, though? You can easily look at the BIPM's reports [0] to get the gist of how they do it. Some of the contributing atomic clocks are aligned to UTC, and others are aligned to TAI (according to the preferences of their different operators), but the BIPM averages all the contributing measurements into a TAI clock, then derives UTC from that by adding in the leap seconds. [0] https://webtai.bipm.org/ftp/pub/tai/annual-reports/bipm-annual-report/annual_report_2020.pdf https://webtai.bipm.org/ftp/pub/tai/annual-reports/bipm-annu...
paulddraper 2y ago
I agree that deviating from MST costs more than it benefits. --- However, this proposal is not entirely pointless. The point is: 1. Existing UTC timekeeping is unmodified. (profoundly non-negotiable) 2. Any two timestamps after 2035 different by an accurate number of physical seconds. --- Given that MST is already a feature of UTC, I agree removing it seems silly.
ForOldHack 2y ago
The hack is literally trivial. Check once a month to see if UTC # ET. If not then create a file called Leap_Second once a month, check if this file exists, and if so, then delete it, and add 1 to the value in a file called Leap_Seconds, and make a backup called 'LSSE' Leap seconds since Epoch. You are not expected to understand this. It keeps both systems in place. If you want, I could make it either a hash or a lookup table.
newpavlov 2y ago
In the ideal world, you are right, computer systems should've been using TAI for time tracking and converted it to UTC/local time using TZ databases. But in the real world a lot of systems made the wrong choice (UNIX being the biggest offender) and it got deeply encoded in many systems and regulations, so it's practically impossible to "just switch to TAI". So it's easier to just re-interpret UTC as "the new TAI". I will not be surprised if some time in the future we will get the old UTC, but under a different name.

phicoh 2y ago

The is no such thing as TAI. TAI is what you get if you start with UTC and then subtract the number of leap seconds you care about. TAI is not maintained as some sort of separate standard quantity. In most (all?) countries, civil time is based on UTC. Nobody is going to set all clocks in the world backwards by about half a minute because it is somewhat more pure. GPS time also has an offset compared to TAI. Nobody care a bout that. Just like nobody really cares about the Unix epoch. As long as results are consistent.

gerdesj 2y ago
The only think we can be certain of is that the Summer Solstice occurs when the mid summer sun shines through a trillithon at Stonehenge and strikes a certain point. From there we can work outwards. The logical thing to do is to precisely model Stonehenge to the last micron in space. That will take a bit of work involving the various sea levels and so on. So on will include the thermal expansion of granite and the traffic density on the A303 and whether the Solstice is a bank holiday. Oh bollocks ... mass. That standard kilo thing - is it sorted out yet? Those cars and lorries are going to need constant observation - we'll need a sort of dynamic weigh bridge that works at 60mph. If we slap it in the road just after (going west) the speed cameras should keep the measurements within parameters. If we apply now, we should be able to get Highways to change the middle of the road markings from double dashed to a double solid line and then we can simplify a few variables. ... more daft stuff ... Right, we've got this. We now have a standard place and point in time to define place and time from. No we don't and we never will. There is no absolute when it comes to time, place or mass. What we do have is requirements for standards and a point to measure from. Those points to measure from have differing requirements, depending on who who you are and what you are doing. I suggest we treat time as we do sea level, with a few special versions that people can use without having to worry about silliness. Provided I can work out when to plant my wheat crop and read log files with sub micro second precision for correlation, I'll be happy. My launches to the moon will need a little more funkiness ...
- ForOldHack 2y ago
  Sorry to say Stonehenge or the plate on which is stands is moving... to the east, but the wobble of the earth is changing.
  - gerdesj 2y ago
    Isn't the Eurasian plate moving widdershins? The Wiltshire Downs and Salisbury Plain is mostly chalk/limestone. That is a porous rock which will expand and contract on water ingress/egress and be affected by atmospheric humidity. I've no real idea but I suspect that Stonehenge will rise and fall vertically(ish) on a seasonal and other longer rhythms.
    - ForOldHack 2y ago
      Widdershins: "in a direction contrary to the sun's course.." Interesting. The Eurasian plate is moving east, which is widdershins to the longitude, but not the latitude. ( Note: I am a Scot, and added widdershins to my dictionary. )
LegionMammal978 2y ago
> The is no such thing as TAI. TAI is what you get if you start with UTC and then subtract the number of leap seconds you care about. TAI is not maintained as some sort of separate standard quantity. There is, though? You can easily look at the BIPM's reports [0] to get the gist of how they do it. Some of the contributing atomic clocks are aligned to UTC, and others are aligned to TAI (according to the preferences of their different operators), but the BIPM averages all the contributing measurements into a TAI clock, then derives UTC from that by adding in the leap seconds. [0] https://webtai.bipm.org/ftp/pub/tai/annual-reports/bipm-annual-report/annual_report_2020.pdf https://webtai.bipm.org/ftp/pub/tai/annual-reports/bipm-annu...

paulddraper 2y ago

I agree that deviating from MST costs more than it benefits. --- However, this proposal is not entirely pointless. The point is: 1. Existing UTC timekeeping is unmodified. (profoundly non-negotiable) 2. Any two timestamps after 2035 different by an accurate number of physical seconds. --- Given that MST is already a feature of UTC, I agree removing it seems silly.

ForOldHack 2y ago

The hack is literally trivial. Check once a month to see if UTC # ET. If not then create a file called Leap_Second once a month, check if this file exists, and if so, then delete it, and add 1 to the value in a file called Leap_Seconds, and make a backup called 'LSSE' Leap seconds since Epoch. You are not expected to understand this. It keeps both systems in place. If you want, I could make it either a hash or a lookup table.

newpavlov 2y ago

In the ideal world, you are right, computer systems should've been using TAI for time tracking and converted it to UTC/local time using TZ databases. But in the real world a lot of systems made the wrong choice (UNIX being the biggest offender) and it got deeply encoded in many systems and regulations, so it's practically impossible to "just switch to TAI". So it's easier to just re-interpret UTC as "the new TAI". I will not be surprised if some time in the future we will get the old UTC, but under a different name.