On 12/2/2018 6:22 AM, John Clark wrote:
On Sat, Dec 1, 2018 at 6:59 PM Brent Meeker <meeke...@verizon.net
<mailto:meeke...@verizon.net>> wrote:
> /But an ocean wave many feet high would change the gravitational
field less than would moving a centimeter relative to the Earth's
center of mass./
Not so. In 1798 technology was good enough for Cavendish to measure
the gravitational attraction between 2 cannonballs a few inches apart
(and by doing so determine the value of the Gravitational Constant)
but until a few months ago no technology was good enough to measure
the difference in strength of a gravitational field that was
637,000,000 centimeters from the center of the Earth and one that was
637,000,001 centimeters from the center of the Earth. But the
technology is good enough nowthanks to this new clock. And this isn't
the end of the line for clock technology, nobody has made one yet but
a Thorium Nuclear Clock would be even more accurate.
No. The potential difference measured by the cesium clock when raised
1cm relative to the Earth was 2.03e9 times bigger than the smallest
difference measured by Cavendish (assuming he could measure 0.00025m
deflection). The Earth is 3.9e22 times heavier than Cavendishes cannon
ball. So 300yrs ago Cavendishes technology was good enough; it's
just hard to hang two Earth masses in a big box.
Brent
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