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Metrologists Seek the Ideal

Posted October 06, 2011 7:00 AM

All but one of the seven fundamental metric units (the kilogram, meter, second, ampere, kelvin, mole, and candela) depend on universal constants, and while there may be a campaign to define Boltzmann's constant more precisely (which could alter the kelvin), at least there is a definition that should be the same around the world. The kilogram is the lone holdout, defined as the mass of a hunk of metal in France. Is that good enough? Or should mass also be tied to a constant? And if so, what that should be?

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Join Date: Jul 2008
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#1

Re: Metrologists Seek the Ideal

10/06/2011 10:42 PM

Work in under way which aims to replace the "hunk of metal: kilogram standard.

One such effort is described here: http://www.csiro.au/news/PerfectKilogram.html

Peter.

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#2
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Re: Metrologists Seek the Ideal

10/07/2011 1:30 PM

So it appears there is still a physical object - now a silicon sphere. Does everybody have to make their own? I don't see the point.

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#3
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Ready to be shot down :)

10/09/2011 5:20 AM

I don't see how making a 'man-made' sphere out of a 'lump of crystal' is going to change the fact that the standard is still not controlled by a definite quantity! You may say that it is the amount of atoms of silicon in the sphere but by their own admittance, their spheres are not perfect. Therefore we are in the same position as before, having to use a man made object as a reference! How hard is it to define a Kilogram using constants? Do we need a physical object at all for the definition? Can we say it is equal to 'x' atoms of whatever element at a 'zero height reference point for sea level' somewhere in the world?

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