On 11/29/2018 6:28 AM, John Clark wrote:
In yesterday's issue of the journal Nature Scientists at the National
Institute of Standards and Technology (NIST) reported they have made a
new type of clock that is the most accurate ever, it's called a
Ytterbium Lattice Clock. It's about 100 times better than any previous
clock, if set at the time of the Big Bang 13.8 billion years ago today
it would be off by less than one second.
https://www.nature.com/articles/s41586-018-0738-2
It's so good the main source of error is due to General Relativity, if
you lift the clock up by just one centimeter the Earth's gravitational
field is slightly weaker and so the clock runs noticeably faster, that
may be why NIST is now working on a portable version of their
Ytterbium Lattice Clock. If GPS satellites had clocks this good they'd
know where they were relative to the Earth to within a centimeter and
so could tell users on the ground where they were within a centimeter;
and that would be more than good enough for jet fighters to
automatically land on aircraft carriers without a pilot, even at night
in a heavy fog in a bad storm with the deck tossing up and down.
Unfortunately for that idea, the surface of the Earth, and especially
the ocean, varies by a lot more than a centimeter. Off the coast of CA
where the Pacific Missile range is, the "Earth's surface" as defined in
WGS84 is a few meters underwater. That's why one must us local
corrections for GPS altitude. But the local correction is still only an
average over tidal cycles, etc.
Brent
It would be by far the best instrument ever made to detect tiny
changes in the gravitational field, and that would make it much easier
to find things buried deep underground. The Earth just became more
transparent. It might even be used to detect Gravitational Waves and
Dark Matter.
John K Clark
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