From The Washington Post: “Scientists are about to change what a kilogram is. That’s massive.”

The Washington Post

July 5, 2017
Sarah Kaplan

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The NIST-4 Kibble balance. The instrument was used to calculate Planck’s constant, an important step toward redefining the kilogram. (Jennifer Lauren Lee/NIST PML)

If Jon Pratt were an international criminal mastermind, he would fly to Paris, don an all-black suit and ski mask and sneak into the elegant French baroque building that serves as headquarters for the Bureau International des Poids et Mesures.

His mission: “To set the whole world’s system of mass into disarray,” Pratt said. “This is my dastardly plan.”

In this hypothetical scenario, Pratt slips past the security guards, disables the alarm system and picks the lock on a temperature-controlled, airtight safe deep in the bowels of the BIPM. Inside, he finds his target: a small platinum and iridium cylinder weighing exactly one kilogram. It’s the kilogram, crafted in 1889 to serve as the single standard by which all other kilograms are measured. People call it “le grand K.”

“I’d take out a nail file, and I’d scratch a little bit off,” Pratt said. Then he’d slip back into the night. “And the next time they take the thing out” (to test the accuracy of the world’s other kilograms) “everything else will be wrong.”

But Pratt is not a criminal mastermind. He’s a public servant, the chief of quantum measurement at the National Institute of Standards and Technology, which oversees weights and measures in the United States. And he doesn’t want to tamper with the global system of mass. He wants to revolutionize it.

Pratt and his colleagues at NIST are part of an international effort to redefine the kilogram based on a fundamental universal constant — a physical quantity in nature, like the speed of light or the electric charge of a proton, that never changes regardless of when and where you are. And on Friday, the NIST team got their most precise measurement ever for this constant.

See the full article here .

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