[time-nuts] UTC and leap seconds
hmurray at megapathdsl.net
Fri Jun 11 16:04:17 UTC 2010
iovane at inwind.it said:
> I was wondering, why we assume that Earth's rotation is slowing down,
> instead that clocks are speeding up?
The quick answer is that there is a mechanism that explains why the Earth is
slowing down: tidal effects. There is no corresponding way to explain why
atomic clocks are speeding up.
How many different timekeeping mechanisms are there that are accurate enough
to notice changes in the Earth's rotation?
Wikipedia says 2 ms/100 years and that it was noticed by Halley in 1695 and
confirmed by Dunthorne in 1749. I assume they were using the Earth's orbit
around the sun as their reference clock.
I think that's 6 parts in 1E12 so it takes a pretty good clock. (I'm
frequently amazed by how good the old astronomers were.)
The Wikipedia article discusses geological evidence: silt layers from 620
million years ago give a calibration on the Earth's rotation and the Moon's
> (Speculative hint: We accept that the universe is expanding. Might this
> affect the fine structure of matter, including cesium atoms? Is there any
> adverse proof? What is easier to think? a) the expansion of the universe
> doesn't affect at all the properties of matter. b) it might.).
It's clearly easier to think that the expansion of the universe doesn't
effect things. Sure, it might, and I expect a few far-out theoreticians are
working on things like that. But nobody has proposed a mechanism yet, nor an
experiment that would measure it. Science is all about measuring. Yes, it's
fun to wave your hands about crazy ideas, but who cares if you can't come up
with something to measure?
I'm not really a physics wizard. There might be some gravity terms or
experiments I've missed. But the universe isn't expanding very fast (at
least not in the local region) so any effect will probably be very hard to
measure. Maybe dark energy will distort time.
These are my opinions, not necessarily my employer's. I hate spam.
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