"The kilogram is dead; long live the kilogram" Topic

Nearly every measurement of weight you've ever made, from peeking at your bathroom scale to measuring out flour for a recipe, can be traced back to just a single object: a metal kilogram made of platinum and iridium that resides under lock and key in an underground vault in Paris. It's called the International Prototype Kilogram, or IPK, and since its creation in 1889 it has been the standard by which the world's weights are defined. But not for much longer.

Copies of the IPK are distributed around the world, with countries then creating their own reference weights, as close to the original as possible. These, in turn, are used to calibrate scales and weights throughout every section of society, from labs and factories to supermarkets and bakeries. And, yes, this includes America. The United States uses pounds and ounces instead of kilograms, but these too are calibrated using the International Prototype Kilogram, just like the metric system.

But later this week, on Friday, November 16th, a coup is planned in this international ministry of weights. After having served for 129 years as the world's standard, the International Prototype Kilogram (or Le Grand K, as it's known locally) will be stood down. Grandees of the International Bureau of Weights and Measures, which regulates the metric system, will gather in Versailles and vote to replace this physical artifact with a definition of the kilogram based on a fundamental constant of nature.

The switch won't be noticed by anyone outside of an advanced physics lab, but is a momentous occasion for those involved. "It is the Halley's Comet of metrology," says Stephan Schlamminger, a physicist from the US National Institute of Standards and Technology (NIST) who worked on the equipment used for the coming changeover. "It's incredibly rare that a redefinition of this magnitude happens."[…]

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Cheers,
Martin from Canada

It's a wonder the Germans didn't make off with the Sacred Kilogram. I guess Goering was too busy stealing decadent nude paintings.

Well the meter used to be the "international prototype metre" or IPM and it's copies. This is a bar of platinum-iridium alloy. However, due to torsional strain when picking up the bar to measure it, and temperature and pressure fluctuations, there was always some (very, very) small error in the length.

That's why the actual meter then became based on radiation cycles from stable isotopes. Therefore a meter is really the "length equal to 1 650 763.73 wavelengths in vacuum of the radiation corresponding to the transition between the levels 2p10 and 5d5 of the krypton 86 atom." If you suffer from insomnia here is what you can read:

PDF link

But recently, they measure the output of a helium-neon laser over time. So now a meter is the length of the path travelled by the laser light in vacuum during a time interval of ​1⁄299,792,458 of a second.

Resolution 2, 15th Meeting of the General Conference on Weights and Measures, 1975.

But determining length is a bit easier than establishing weight.

Winston, you only took one sentence in one entry to illustrate Godwin's Law.

…and on the initial response to the thread! Genius!!

My scientific ignorance knows no bounds, but that article was damn interesting. Thanks, Martin.

And the vote passed unanimously.

I invoked Goering. Not the other guy with the bad mustache.

Chemistry was simpler.
The Carbon12 isotope was DEFINED as being exactly 12.0000000000 grams per mole? Or was the mole defined by so many atoms of Carbon12? Or was it a circular definition? A tautology!
I suppose "they" have changed all that too since the last time I wore a white coat.

It was a interesting artical

I invoked Goering. Not the other guy with the bad mustache.

I don't think Godwin cared which specific Nazi was invoked.

was the mole defined by so many atoms of Carbon12?

Yes. Avogadro's number.

The Carbon12 isotope was DEFINED as being exactly 12.0000000000 grams per mole?

I thought that the carbon12 isotope is defined as having 6 neutrons and 6 protons.

I think the kilogramme should be set as 1/200th of Neil degrasse Tyson's big fat momma.

Carbon 12 was defined as being exactly 12 grams per mole. Add as many zeroes as you wish.
However, in calculating molecular weights, you had to use 12.01 because of those pesky C13 and C14 isotopes present.