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Comment by ghshephard | Hacker News Reader

You have one of my favorite comments on this entire thread - so I'm interested in your thoughts on who leap seconds are useful for, if not Astronomers (and clearly not Meta).

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They are useful for ordinary people. Without them, at some point in the future people would go to work at 8am at sunset and go to bed at sunrise. Leap seconds are a way for everyone to agree to shift their schedules by 1 second to stay in sync with solar time. It's subtle enough that most people don't even know they exist, nor will it have an effect on most systems. Larger jumps would be much more difficult to ignore, and smaller jumps would be more frequent.

How long from now are you talking about? Eyeballing it, I think it would take us about a thousand years to get off by an hour?

In the worst case, you would get 2 leap seconds per year. So in the worst case, 1800 years.

However, in the past 50 years, we've only had 27. So at the current rate, probably more like 6667 years to be off by an hour.

Of course, if the earth's rotation changed speed by so much that 2 leap seconds per year wasn't enough, we'd find a way to cram more in. In fact, in that case, the case for leap seconds would probably get stronger.

I would absolutely take the cost of work schedules being adjusted by an hour once every 6667 years over the cost of 6667 years of programmers having to deal with leap seconds and everyone else having to deal with the fallout of any bugs from that.

How long has the 9-5 even existed? Less than 200 years? At no point in 6667 years would anyone notice any consequences of the drift, culture and work schedules change so much faster than that.

> How long from now are you talking about? Eyeballing it, I think it would take us about a thousand years to get off by an hour?

The Julian calendar being off with regards to leap years wasn't a problem… until it was. And then someone had to fix it:

* https://en.wikipedia.org/wiki/Gregorian_calendar

We change our clocks twice a year by an hour I think we could handle an hour every millenia.

And, by some accounts, every time we do, auto deaths and other bad things increase for some period after the change. Not to mention the weeks of bitching on either side of the change about how bad/great the time change actually is.

One second every thousand years.

Do you mean one hour?

Yeah, one hour. Whoops.

> Yeah, one hour. Whoops.

I think your comment is a precursor to what would happen if we tried to get a one-off event right…

Right I'm sure we'll forget.

The physical effort of setting a clock is not the issue. Switching to "leap hours" would involve a good part of the world living with about 9am sunrise (or a 3:30pm sunset) for hundreds of years. It'd be a really hard sell to say that's actually better. DST is adjusting to the amount of daylight available, so there's not much of a negative impact. Systems that need to be more accurate just set their time zones to UTC. And one second every year or so is far within the accuracy of a typical computer clock, so anything that needs something better is already going to have a complex time synchronization system.

Yeah how ever will they live with having to wake up slightly earlier or later for their entire lives.

> earlier or later

My understanding was that leap seconds are only ever added. It’s not like this averages out over time. The problem is that because they are only added the effect is cumulative and eventually some future generation will be eating lunch at 00:00:00.

There is a provision for negative leap seconds. In practice, this has never happened.

Thanks, I skimmed the wiki and it sounded like they could only be added.

Hasn't happened, but it may actually happen in the next half-decade or so. If not, it's almost guaranteed to happen ~25 years from now.

So what is it about a system where everyone and every business adjusts their schedule slightly (I guess independently) of each other that is better than the leap second system we have now. Which, as I said earlier, is essentially the same thing, but done in a standardized way.

Timekeeping at the abstraction level where business hours exist is a lot more tolerant of 40 seconds of error than at the abstraction level where timekeeping primitives are implemented.

> a good part of the world living with about 9am sunrise (or a 3:30pm sunset) for hundreds of years

So no real change to the status quo?

For humans, it's no worse than folks today who live on a time zone boundary and cross it often. You might argue that for humans, the local solar time should be computed as a continuous function of longitude, leap seconds can be managed there, and we get rid of the concept of a time zone.

Computers are another story though, perhaps in the past "a typical computer clock" could be on the order of seconds off and be fine. When computers start to control things like wireless networks (cellular is a problem today, time accuracy is a design factor in evolving Wifi as well), those seconds turn into microseconds very, very quickly. The whole point of the article is to reduce unnecessary complexity in the existing complex time synchronization systems.

If you're running large infrastructure, the next leap second is going to cause an outage somewhere in your org, and the cost may be very large.

> Switching to "leap hours" would involve a good part of the world living with about 9am sunrise (or a 3:30pm sunset) for hundreds of years.

Can we switch to leap minutes instead? In the worst case it would mean to adjust the time once in 30 years, which means that astronomers and software engineers would have to deal with this problem no more than 3 times in a century. Fair enough IMHO.

> We change our clocks twice a year by an hour I think we could handle an hour every millenia.

And how often does time code mess that up? We have leap years regularly every ~4 years, and how does time code mess that up?

And you think that a one-off event is going to go smoothly?

The "ordinary people" really don't care about leap seconds. Like really, really not.

It's less than a minute in a life span. Just skip summer time once every millenium something.

This isn’t what would happen. Even we had a huge number of inexplicably needed leap seconds (there are 3600 seconds in an hour), local offsets would just change, for the same reason that people on the other side of the planet have a different time on their watch than you do. And if for some reason we proved incapable of doing that, then social conventions on when the work day started would shift relative to the local time. There just is no danger of people going to work at sunset.

I’m not saying that abandoning leap seconds is a good idea, just that abandoning them wouldn’t consign future generations to whacky schedules.

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