From: Eugen Leitl (firstname.lastname@example.org)
Date: Tue Dec 09 2003 - 12:18:43 MST
On Tue, Dec 09, 2003 at 10:08:13AM -0800, Tomaz Kristan wrote:
> Quoting: "The second is the duration of 9192631770
> periods of the radiation corresponding to the
> transition between the two hyperfine levels of the
> ground state of the cesium 133 atom."
Yes, it's a nuke clock. Counting oscillations of a very
> Quoting: "The meter is the length of the path traveled
> by light in vacuum during a time interval of
> 1/299792458 of a second."
Fabry-Perot interferometry was stard in metrology labs
even before 1960.
> Now, who counts those two numbers? Nobody. It's a
Actually, yes, they do. Not necessarily directly.
> definition free of any reference to an artifact, and
> that is the beauty. If we could (and we could) define
Any fool can whip up random standard definitions.
The difference between a good one and a lousy one is
that a good one is actually easy to measure. This of
course shifts as technology advances.
Care to design a decent clock standard, something good
enough for posthumanity? (I have a design, but I'm interested
what other people will come up with).
> kilogram in the same manner, we would be able to
> transmit all physical data across the Galaxy, without
> sending "the cylinder" also.
Which why people are pressing forward to using Avogardro
number of a standard mass isotope to derive the kg standard.
Notice that in a pinch you can fab your kg standard
by mechanosynthesis of a C-12 diamond crystal.
> It would be a Western civilization context independent
> definition! What the silicon sphere or iridium cylinder
> - aren't. ;-)
The PSE is the same around the cosmos, dunno about numbers.
Hence PtIr is a lousy standard, but the Si sphere is not
(because it's a roundabout way to the Avogadro number).
-- Eugen* Leitl leitl
ICBM: 48.07078, 11.61144 http://www.leitl.org
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