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0 pointswongarsu4y ago0 comments

> There’s really no such thing as exact time. The closest is UT1, and it’s not really practical for normal applications.

I would have defined TAI (International Atomic Time) as "exact time". Of course with it being an average of clocks it only really exists in hindsight and isn't perfect either, but if you only need accuracy on the order of hundreds of nanoseconds and are on earth's surface it's very practical and easy to get anywhere with a GPS receiver.

And UTC is only slightly more messy, with its offset from TAI to keep it in sync with unpredictable UT1.

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4 comments · 1 top-level

tialaramex4y ago· 3 in thread

Right. It's crazy that we welded civil time to UT1 rather than TAI. TAI is ours, we made it, here on this rock we're all stuck on. Because time is necessarily relative to your position that's the best we could hope for.

The astronomers are welcome to UT1, it's useful for them and I have no problem with that, but it's crazy to keep tweaking UTC to match UT1 rather than just letting it plod along mechanically forever with TAI. Abolish leap seconds.

layer84y ago

This will create problems in the long term, because the delta-T due to the deceleration of earth’s rotation due to tidal friction increases quadratically [1]. Not saying it wouldn’t be practical, but that’s the debate, along with astronomer’s needs, satellite navigation etc. You can’t just ignore the relationship with earth’s rotation.

[1] e.g. https://www.researchgate.net/figure/Observations-and-parabol...

tialaramex4y ago

> You can’t just ignore the relationship with earth’s rotation.

Doing so is, in fact, the point of abolishing leap seconds.

Imagine that we have leap seconds, and the very worst case conceivable happens for an entire century. 100 summer leap seconds and 100 winter leap seconds, that's a total of just over three minutes by 2122.

Can we tolerate such a disruption to the lives of ordinary people? Try asking anybody who lives in a place with Daylight Saving or "Summer" Time. They have twenty times more disruption and that happens twice every single year.

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BenjiWiebe4y ago

Let's just outlaw deceleration of the earth, and while we are at it, mandate that the sun rises and sets at the exact same time every day.

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