It’s Time To Redefine The Kilogram


And it’s in this case where we can witness another benefit of the redefinition. If you fix the mass to a fundamental constant, you can define any mass you like (you won’t have to start with a kilogram and subdivide). The redefinition would improve the whole mass scale.

If you think that the redifnition is a straightforward easy process, though, we've got bad news for you. To accept the new measurements, the CIPM requested that three independent measurements be obtained with at least two independent methods. And this is where things get a bit complicated.

The international unit of electric current, the ampere, has been defined in relation to the kilogram, but the electrical community has found ways to establish the ampere in terms of certain quantum effects connected to the Planck constant.

What scientists thought of doing was to turn the definition of the ampere on its head and to define the kilogram through electric units in terms of the Planck constant.

The instrument to perform this measurement, known as the watt balance, was invented by Dr Bryan Kibble in 1975. Dr Kibble passed away this year, and the instrument has been renamed the Kibble balance in his honor. The Kibble balance is essentially a very complex scale.

Scientists are currently working on the highest precision measurement of the Planck constant. Once that is obtained, the Kibble could be used to measure the mass of any object.

“Theoretically, anyone could build their own Kibble balance, do the experiment, and then generate a ‘kilogram’ without having to wait,“ explained Dr Davidson.

Section of the Kibble balance. National Physical Laboratory. 


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