Nov 17 2018
08:03 am

So apparently, since 1875 a kilogram has been defined as the weight of a precisely machined cylinder of platinum-iridium metal stored in a vault in Paris. Exact copies were distributed around the world for reference and calibration.

But, scientists found that the original kilogram has lost weight and its replicas no longer matched. So they set out to fix it.

On Friday, the International Bureau of Weights and Measures agreed that a kilogram is now based on universal mathematical constants:

The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.626 070 15 × 10–34 when expressed in the unit J s, which is equal to kg m2 s–1, where the metre and the second are defined in terms of c and ∆νCs.

This means that a kilogram is now the same everywhere on Earth and anywhere in the universe. Or something like that.

The new definition is based on Planck's constant. But there first had to be agreement on its value. This involved several years of complex research.

Now if we could just convert to metric. Did you know that the U.S. is one of only three countries that don't use the international standard metric system? (The others are Myanmar and Liberia.)

Further reading:

BBC: Kilogram gets a new definition

NYT: The Kilogram is Dead. Long Live the Kilogram!

PBS: The new definition of the kilogram will change the way we weigh everything

JR01's picture

Metric system has its benefits

But if anyone thinks that big oil isn’t going to take advantage of this and charge us by the liter, they are not very smart. Europe pays the equivalent of $7-8 per gallon of gas, and that would cripple the entire country.

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