Re: BIPM decides to stop adding leap seconds to UTC

Context: BIPM is responsible for the UTC time standard, and in this document they decide to stop adding (or removing) leap seconds, starting on 20th of May 2027 and lasting for the foreseeable future (until one leap hour is needed, but even then it's unclear if they'll do something). Together with the decision to not add a leap second in December, the 27 leap seconds that have been added so far should be the only ones, ever.

The page lists several good reasons for this, including:

- It's a common source of bugs.

- Solar time is not that important in a world of coarse timezones.

- IoT and anything that cannot receive time updates have trouble with leap seconds.

- Negative leap seconds have never occurred before, but might occur in the future, and almost no software has tested this case.

I'd also add:

- Unix timestamps are actually defined as "seconds since epoch minus however many leap seconds have happened". It's a hack to keep code that assumes "86400 seconds in a day" from breaking. It means that during a leap second the Unix timestamp goes back and repeats a previous value, making them ambiguous and non-monotonic.

- Leap second unpredictability can make it impossible to calculate how many seconds are between two UTC dates or Unix timestamps, for example the countdown to the year 2038 bug.

- The proper ISO8601 formatting of leap seconds ("23:59:60") is widely unsupported, breaking parsers, along with the assumption of how many seconds are in a minute, hour, or day.

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EDIT: I've emailed hn@ycombinator.com to change the title. It's avoiding editorialization, but I think it's also preventing the post from getting the attention it deserves.

I'm booking a yearly one-second-long holiday on my calendar, to celebrate all the headaches this will save me. Happy end of leap seconds!

BoppreH, 23 hours ago