Advertisement

The Definition Of A Kilogram Officially Changes Today

It's World Metrology Day and as a gift to us all, the scientific community has officially changed the definition of the kilogram. 

Don't panic -- you're not suddenly going to weigh more.

For the past 130 years, a cylinder of a platinum-iridium alloy known as the 'Grand K' has been the official definition of a kilogram -- the global standard of exact mass.

The lump of metal, which is stored in a vault in France, has served us well but it isn't perfect.

A mass etalon, a copy of the original 'Grand K' rests under its double glass dome during the International General Conference of Weights and Measures. Image: EPA

Every time scientists handle it, the cylinder loses atoms, thereby changing its mass. The Grand K is estimated to have lost about 50 micrograms in its life.

So, beginning today, the kilogram will officially be measured by a physical constant of nature known as the Planck constant.

It looks like this -- 6.62607004 × 10-34 m2 kg / s.

Heavy science, right?

It is derived from quantum physics, and with a Kibble balance -- a flawlessly accurate weighing machine -- can be used to calculate the mass of an object by using a precisely measured electromagnetic force.

READ MOREThe Kilogram As We Know It, Is No Longer

None of this is going to change the way you weigh your veggies at the supermarket or come to terms with how much you ate over Christmas, but for the scientific community, it is a historic moment.

“Measurement underpins science, trade, and industry," Chief Metrologist of the National Measurement Institute, Doctor Bruce Warrington said.

"For global trade and international collaboration it is important to speak the same language of measurement, expressed in common units like the second, the metre, and the kilogram."

Warrington said while the Grand K has been accurate enough for many purposes, scientists today need even greater levels of accuracy, especially when working with tiny masses like drug molecules in pharmaceutical research.

The switch to the Planck constant has been years in the making. Measurement scientists from around the world came together in Paris in November to vote for the redefining of the International System of Units, which includes the kilo.

A group of U.S. researchers were so proud of the auspicious moment, they got the re-defined unit tattooed onto their arm.

The definitions of four of the seven base SI units will change on Monday.

While the kilogram will be based on the fixed value for the Planck constant, the ampere (for electric current) will be based on the charge of the electron, the kelvin (for temperature) on the Botlzmann constant, and the mole (for amount of substance) for the Avogadro constant.