[sla29970]

In 1950 astronomers pointed out that there would have to be two kinds of time, one to agree with calendar days and one to be as uniform as possible. Arguments over subsequent decades inexplicably decided that there could only be one kind of time specified by international agreements, and we ended up with a choice of two out of three characteristics in what we now call UTC. https://www.ucolick.org/~sla/leapsecs/picktwo.html

[zokier]

You website is a true hidden gold nugget, thanks for putting in the time to write all that up.

As an expert (as far as anyone around here is), what would your pick be for common civil time? Personally I feel like "precise time and simplicity" is almost obvious choice, but apparently it is not quite that clear cut.

[bloak]

"Simplicity" is rather subjective, even if you answer the question: simple for who?

Civil time has to stay in phase with the sun. As I see it, that's not negotiable. Inserting leap seconds, so that the nanosecond field of UTC remains the same as the nanosecond field of TAI, and the jumps that occur are negligible for ordinary people, seems to me overall the simplest solution, though I can see that UTC-SLS would be simpler for some people in some situations, and switching to leap minutes or leap hours would be simpler for people living now, who could then just ignore the problem. (Pollution and global warming and lots of other things can be treated in the same way, of course. Perhaps some of these things really will be easier to solve in the future, but I'd rather not rely on it.)

[zokier]

> "Simplicity" is rather subjective, even if you answer the question: simple for who?

I used simplicity in the meaning provided by link in parent comment refering to three desirable properties of time systems: "Every "day" has 86400 "seconds" (606024)."

> Civil time has to stay in phase with the sun. As I see it, that's not negotiable.

I don't see why that needs to be the case on a seconds level.

> switching to leap minutes or leap hours would be simpler for people living now, who could then just ignore the problem. (Pollution and global warming and lots of other things can be treated in the same way, of course. Perhaps some of these things really will be easier to solve in the future, but I'd rather not rely on it.)

Considering that need for leap hour would appear in over 500 years, I feel like trying predict the situation then is really borderline overarrogant.

Also leap hour would be basically a timezone shift, and I bet we will be doing timezone changes anyways in the next 500 years

[bloak]

Not at all. Just because it involves an "hour", rather than a "second", doesn't mean that it resembles a "timezone shift". It's totally different.

With a timezone shift, all that happens is that "09:00:00 +0900" is the same as "10:00:00 +1000". We can cope with that. But if you make UTC jump back an hour, then we have "09:59:59 +1000" followed by "09:00:00 +1000", and then the whole previous hour happens again. The internal timestamps in computer systems (typically expressed as a number of seconds since some epoch) repeat themselves for an hour. Causality is violated. Most computers stop working. You would probably have to switch them off beforehand to prevent data loss and even longer interruptions to service. You could shut down all the servers and desktop machines, stop all public transport and so on, but you can't just turn off the computers in embedded systems and satellites and so on...

So let's not try to arrogantly predict the situation in 500 years. Let's carry on with the established system of leap seconds, at least until someone comes up with a sensible alternative. Then there won't be a "situation" in (less than) 500 years.