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Comment by igul222 | Hacker News Reader

What makes the metric system appealing is that each physical quantity has exactly one "base" unit, and you can make easy conversions– just multiply or divide by 10.

The thing about time is, there are two important 'natural' units that aren't going away: the day and the year. Whatever system you devise has to include them somehow. And unfortunately, the conversion factor between them (365) isn't a multiple of 10.

That said, we can do a lot better than the status quo. Since we've already given up on the idea of having a single base unit for everything, why not express time in fractions of days instead of multiples of seconds? Counting time up to 1.0 days is a lot more intuitive than counting up to 8.64 myriaseconds. The second is a unit of time which isn't tied to anything intuitive (actually, it's entirely arbitrary). If we're going to shake things up, let's at least use days instead, yeah?

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The problem with days and years is that they change as the Earth's velocity varies over time. You can't use days and years for scientific work unless you define a specific unchanging length for them, but if you do that they will soon get out of sync with the Earth's rotation.

You could come at it in a similar way to how the real second was developed. Initially the second was defined as 1/86,400th of a day, later narrowed to a mean solar day, but that still wasn't specific enough so they switched it to the current caesium atom definition.

If we wanted to subdivide the day into 100,000 new units instead of 86,400 seconds, we could simply take the current caesium atom definition * 864,000 / 100,000 and you would get a precise, scientifically acceptable unit that would be about 1/100,000 of a day, but still have the need for the occasional leap units.

I'm not suggesting replacing the second for scientific work-- that would be a mess, I agree. But since it seems the day is already good enough for casual timekeeping, why not replace the non-scientific, imprecise, everyday uses of second/minute/hour with fractions of the day?

> Counting time up to 1.0 days is a lot more intuitive than counting up to 8.64 myriaseconds. The second is a unit of time which isn't tied to anything intuitive (actually, it's entirely arbitrary). If we're going to shake things up, let's at least use days instead, yeah?

No. The length of a day is not constant. The size of a second is defined based on the length of the day in 1900.

Ouch. That impacts a lot of physical definitions, like joules. -edit- On re-reading, I guess you weren't proposing changing the second, right?

Yes. There is a reason why we fiddle with stuff like leap-seconds instead of simply letting the second dilate ever so slightly, as Earth's rotation slows down ever so slightly, so that there are still exactly 86,400 seconds in a day.

Since 1967, the second has been defined as 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.† The caesium atom is far more consistent than the Earth.

†http://en.wikipedia.org/wiki/Second

They're proposing changing the second and you're correct that it will mess up a ton of other units. The problem is they think the day is the base unit when it's actually the second.

What do you do when the length of the day changes? Earth is slowing down.

http://en.wikipedia.org/wiki/Fluctuations_in_the_length_of_d...

Let's not mix metric with decimal. Thes are two different concepts.

https://en.wikipedia.org/wiki/Metric_time

https://en.wikipedia.org/wiki/Decimal_time

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