Re:Hate leap seconds? Imagine a negative one
by fanf2 on Thursday January 13, 2022 @05:06PM
(#29927579)
Right, but general relativity matters for how astronomers define their timescales, and how they are measured and maintained in practice: there are different scales for barycentric time (at the centre of gravity of the solar system), geocentric time (centre of the earth) and terrestrial time (on the surface of the rotating geoid). TAI is supposed to tick at the same rate as TT, so it depends on a model of an equal-gravitation version of sea level (the geoid) and the relative height of the time labs. In particular, NIST is a mile high in Colorado so their clocks tick a lot faster than (say) NPL by the Thames in west London.
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Re:Hate leap seconds? Imagine a negative one
by tialaramex on Thursday January 13, 2022 @07:11PM
(#29928856)
Sure, the quest for Universal Time is despite the name necessarily a local quest so you can't meaningfully export your results to creatures orbiting a distant quasar as you can with the SI units.
But the size of the discrepancy between Colorado and London is far smaller than the discrepancy Leap Seconds are concerned with right?
Re:Hate leap seconds? Imagine a negative one
by fanf2 on Thursday January 13, 2022 @07:23PM
(#29928951)
Yeah, gravitational time dilation is about 1e-16 seconds per metre of elevation near the surface http://leapsecond.com/great2016a/index.htm so Boulder is about 1e-13 fast. The rotation of the earth is stable to about 1e-9 http://leapsecond.com/ten/ which is also about the same as the rate difference between UT1 and UTC (0.2 ms / 86400).
Re:Hate leap seconds? Imagine a negative one
by sla29970 on Monday January 17, 2022 @01:31AM
(#29963920)
During the discussions leading to the inception of the SI second the bigwig standards folks nixed the consideration of relativity, basically paraphrased as "If you physicists do not stop arguing about relativity we will never redefine time in a way that removes it from the astronomers."