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Fri Nov 16, 2018, 11:21 AM

It's official -- a kilogram isn't what it used to be [View all]

Source: Associated Press, via CBC

It's official -- a kilogram isn't what it used to be

Key measurement units kelvin, ampere and mole also get new definitions in Friday vote in France

The Associated Press Posted: Nov 16, 2018 8:17 AM ET Last Updated: an hour ago

The international system of measurements has been overhauled with new definitions for the kilogram and other key units.

At a meeting in Versailles, France, countries have voted to approve the wide-ranging changes that underpin vital human activities like global trade and scientific innovation.

The most closely watched change was the revision to the kilo, the measurement of mass.

Until now, it has been defined as the mass of a platinum-iridium lump, the so-called Grand K, that is kept in a secured vault on the outskirts of Paris. It has been the world's one true kilo, against which all others were measured, since 1889.

Read more: https://www.cbc.ca/news/technology/kilogram-ampere-mole-definition-1.4908449

All that's left is for Betsy DeVos to require that the Biblical version be taught too.

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The Washington Post had a better story, but it was dated yesterday.

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Dave Weigel Retweeted


Are you ready to be inspired .... by measurement?

Tomorrow, people from around the globe will come together to *agree* on something, even though it is hard, even though it is costly, because it reflects a fundamental fact about the universe

A massive change: Nations redefine the kilogram


By Sarah Kaplan November 15 at 7:27 PM

Humanity just made a weighty decision. On Friday, representatives of more than 60 nations, gathered in Versailles, France, approved a new definition for the kilogram.

Since the 19th century, scientists have based their definition of the fundamental unit of mass on a physical object -- a shining platinum iridium cylinder stored in a locked vault in the bowels of the International Bureau of Weights and Measures (BIPM) in Sevres, France. A kilogram was equal to the heft of this aging hunk of metal, and this cylinder, by definition, weighed exactly a kilogram. If the cylinder changed, even a little bit, then the entire global system of measurement had to change, too.

With Friday's vote, scientists redefined the kilogram for the 21st century by tying it to a fundamental feature of the universe -- a small, strange figure from quantum physics known as Planck's constant, which describes the smallest possible unit of energy.

Thanks to Albert Einstein's revelation that energy and mass are related, determining exactly how much energy is in that unit can let scientists define mass in terms of Planck's constant -- a value that should hold up across space and time -- rather than relying on an inconstant metal cylinder. (Mass determines something's weight, and for most purposes mass and weight are interchangeable.) ... The redefinition is the result of a decades-long, worldwide quest to measure Planck's constant precisely enough that the number would stand up to scientific scrutiny.

Sarah Kaplan is a science reporter covering news from around the nation and across the universe. She previously worked overnights on The Washington Post's Morning Mix team. Follow https://twitter.com/sarahkaplan48

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