Definition of the kilogram set to change

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SPL

Scientists are ready to change the way the kilogram is defined.

Currently, it is defined by the weight of a platinum-based ingot called "The Big K" that is locked in a safe in Paris.

Researchers should vote to eliminate it in favor of the definition of the kilogram in terms of electric current.

The decision must be taken at the General Conference of Weights and Measures in Paris.

But some scientists such as Purdey Williams of the National Physical Laboratory have mixed feelings about change.

"I have not been working on this project for too long, but I feel a strange attachment to the kilogram," he said.

"I think it's such an exciting thing and it's a very big moment, so I'm a little sad about (the change)." But that's an important step forward and the new system will work so much better so it's also a really exciting time, and I can not wait for that to happen. "

Why kill the kilogram?

The Grand K has been at the forefront of the international weight measurement system since 1889. There are also several close replicas.

But the days of the master kilogram are numbered. Its weight has changed over the years as it has deteriorated. The kilogram, like the pope, is infallible, so you have to adjust the other weights accordingly.

In a world where precise measurements are now essential in many areas, such as drug development, nanotechnology and precision engineering, those responsible for maintaining the system plan to reverse the increasingly failing rule of The Big K

How is the Big K?

The fluctuation is about 50 parts on a billion, less than the weight of a single eyelash. But even if it is minimal, the change can have important consequences. Dr. Stuart Davidson, who is responsible for mass spectrometry at the NPL, said he was more stable, more precise and more egalitarian.

"By comparing the kilogram in Paris with all the kilogram copies sold around the world, we know that there are discrepancies between them and the Grand K itself," he said.

"This is not acceptable from a scientific point of view, so even if The Big K is adapted to its mission at the moment, it will not be in 100 years."

How does the new system work?

Electromagnets generate a force. Scrap yards use them on cranes to lift and move large metal objects, such as cars. The traction of the electromagnet, the force that it exerts, is directly related to the amount of electrical current flowing through its coils. There is therefore a direct relationship between electricity and weight.

Thus, in principle, scientists can define a kilogram, or any other weight, in terms of the amount of electricity needed to neutralize its force.

Here is the most delicate part

There is a quantity that relates the weight to the electric current, called the Planck constant – named after the German physicist Max Planck and designated by the symbol h.

But h is an incredibly small number, and to measure it, Dr. Bryan Kibble, a research scientist, has built a series of extremely accurate scales. The crunchy scale, as we know it now, has an electromagnet that lowers on one side of the scale and a weight – a kilogram for example – on the other.

The electric current flowing through the electromagnet is increased until both sides are perfectly balanced.

By measuring the current traversing the electromagnet with incredible precision, the researchers were able to calculate h with an accuracy of 0.000001%.

This advance paved the way for the deposition of The Big K by "Die Kleine h".

What are the advantages of the new system?

Every few decades, all replicas of kilograms in the world must be checked against The Great K. The new system, if adopted, will allow anyone with a Kibble scale to check his weight. when and where, according to Dr. Ian Robinson of NPL.

"It's really good to be at this point, I think it's the right decision, once we've done that, it will be stable for the foreseeable future," he said. -he declares.

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