3 ms·
Right, but general relativity matters for how astronomers define their timescales, and how they are measured and maintained in practice: there are different sca
by fanf2 5y ago
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.
- tialaramex 5y agoSure, 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?
- fanf2 5y agoYeah, gravitational time dilation is about 1e-16 seconds per metre of elevation near the surface http://leapsecond.com/great2016a/index.htm 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/ http://leapsecond.com/ten/ which is also about the same as the rate difference between UT1 and UTC (0.2 ms / 86400).
- sla29970 5y agoDuring 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."