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NIST Wants An Electronic Kilogram
Dearing writes "According to the Global Engineering Journal, NIST, those not-so-standard standards people, want to give up the hunk of metal they've been calling a kilogram, even though it never weighs the same twice. In it's place, an electronic kilogram could act as the permanent standard."
(one of) NIST's own web page(s) on this is at http://www.eeel.nist.gov/811/elec-kilo.html. There's a lot more technical detail there than at the link given in the article.
This really does make sense to replace the artifact with something independent -- they have a bunch of "voodoo" every time they measure the current kilo to try to get the same answer.
that wouldn't work - after all, then you've just scaled the problem down to ask "whats the weight of a proton"
remember that the base physical units have to be directly related not to theor, but to empirical observation. That's the difference between "units" and "physical quantities"
MASS is a physical quantity. "kilogram" is a "unit" of that quantity. defining it in terms of the "mass of a proton" makes no sense because thats essentially a *circular* argument.
if you;re gonna construct a vast edifice of science, the foundation better be damn rigorous! this isnt just semantics, its essential, the way that we have to be absolutely sure that 2 + 2 = 4 (which can be derived from the Completeness property of the Real number Set). A good reference for basic units and quantities is here.
Don't blame me - I voted for Howard Dean. http://dean2004.blogspot.com
According to NIST [nist.gov], they've got a variance on the order of 3% per century in the observed mass (probably measured by weight) of the
standard kilo brick.
3 percent??? Do you have any idea how HUGE a variation that would be in a primary standard? Maybe if they polished it with a belt sander before every measurement...
The link you provided says:
[...]are causing the mass of the kilogram to vary by about 3 parts in 108 per century relative to sister prototypes.
Now I'm not certain about this, but I'd wager that the "108" is actually a "10 to the 8th power" that got mangled somewhere in the conversion to HTML. If so, it would represent a more plausible 0.000003% per century variation.