[time-nuts] Calibration and temperature

Poul-Henning Kamp phk at phk.freebsd.dk
Fri Nov 28 14:38:39 EST 2008

In message <6D3AC52128424986A16AB823763F4AEE at cyrus>, "Bill Hawkins" writes:

>Seems to me that all physical quantities have to be calibrated against
>standards, because they're all defined by humans, starting with the
>length of the king's arm.

For several decades now, the metrological community has been on a steady
march away from "artifact based" standards to "physical phenomena"

For instance the measure of length is no longer a piece of metal in Paris
but a given number of wavelengths of a particular spectral line under
certain conditions.

The biggest missing piece is the kilogram, where the two best contenders
are both too unmanageable still:

One contender is a perfect sphere of silicon-28 is so state of the
art that it takes russia to separate the isotopes, germany to make
a crystal and australia to polish it into sphere.
The point is that if the crystal is perfect and the spherical form
is prefect, you can calculate how many atoms there are.

The other contender is the "Watt-balance", where in essense you link
energy spent in an electro magnet to force, and from force to
mass using newtons 2nd law:

So overall, the strategy is to find physical phenomena which are locally
reproducible, exactly like the second is derived from Cs-133 atoms,
instead of comparing to "random artifacts".

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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