Posted on 09/12/2007 2:47:48 PM PDT by decimon
By JAMEY KEATEN, Associated Press Writer 6 minutes ago
PARIS - A kilogram just isn't what it used to be. The 118-year-old cylinder that is the international prototype for the metric mass, kept tightly under lock and key outside Paris, is mysteriously losing weight — if ever so slightly.
Physicist Richard Davis of the International Bureau of Weights and Measures in Sevres, southwest of Paris, says the reference kilo appears to have lost 50 micrograms compared with the average of dozens of copies.
"The mystery is that they were all made of the same material, and many were made at the same time and kept under the same conditions, and yet the masses among them are slowly drifting apart," he said. "We don't really have a good hypothesis for it."
The kilogram's uncertainty could affect even countries that don't use the metric system — it is the ultimate weight standard for the U.S. customary system, where it equals 2.2 pounds. For scientists, the inconstant metric constant is a nuisance, threatening calculation of things like electricity generation.
"They depend on a mass measurement and it's inconvenient for them to have a definition of the kilogram which is based on some artifact," said Davis, who is American.
But don't expect the slimmed-down kilo to have any effect, other than possibly envy, on wary waistline-watchers: 50 micrograms is roughly equivalent to the weight of a fingerprint.
"For the lay person, it won't mean anything," said Davis. "The kilogram will stay the kilogram, and the weights you have in a weight set will all still be correct."
Of all the world's kilograms, only the one in Sevres really counts. It is kept in a triple-locked safe at a chateau and rarely sees the light of day — mostly for comparison with other cylinders shipped in periodically from around the world.
"It's not clear whether the original has become lighter, or the national prototypes have become heavier," said Michael Borys, a senior researcher with Germany's national measures institute in Braunschweig. "But by definition, only the original represents exactly a kilogram."
The kilogram's fluctuation shows how technological progress is leaving science's most basic measurements in its dust. The cylinder was high-tech for its day in 1889 when cast from a platinum and iridium alloy, measuring 1.54 inches in diameter and height.
At a November meeting of scientists in Paris, an advisory panel on measurements will present possible steps toward basing the kilogram and other measures — like Kelvin for temperature, and the mole for amount — on more precise calculations. Ultimately, policy makers from around the world would have to agree to any change.
Many measurements have undergone makeovers over the years. The meter was once defined as roughly the distance between scratches on a bar, a far cry from today's high-tech standard involving the distance that light travels in a vacuum.
One of the leading alternatives for a 21st-century kilogram is a sphere made out of a Silicon-28 isotope crystal, which would involve a single type of atom and have a fixed mass.
"We could obviously use a better definition," Davis said.
Must we always talk politics? :-)
someone cleaned it and didn’t tell anybody?..........
Rusty? Izat you?
Yes.
Proton decay. Of course that’s A LOT of protons.
Rusty? Is that you?
Good thought, but the copies are being weighed in the small local gravity field as the original.
That's it. Sarkozy brought gravitas.
I thought the gram (a thousand of which make up a kilogram) is just the weight of a cubic centimeter of pure water.
The centimeter in turn was taken from a measure of the earth’s arc and then brought down to a usable dimension. This was done, I believe, at the behest of the French Revolution’s drive for objective standards.
Heck, that is what I learned in physics.
Slow release of gases entrained during the original casting process?
While the Metrologists were out to lunch, the cleaning lady, from Chad, came in and saw it was kinda dull, so she polished it for them............
I bet she ain’t never polished a shiny knob in her life!................
Everything looses weight over time (except my wife). My one pound of coffee (16 oz) is now 11.5 oz.
Yep, rust in my joints and some spare mass around the middle, too.
ML/NJ
Don’t be crazy, go with the Hardy Planck
you’ll be glad you did.
*ahem* So what am I? Chopped liver???
See post #23...
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