NRC scientist given weighty task of choosing new kilo

The future of the kilogram hangs in the balance this week as scientists and diplomats from around the world meet in France to vote on whether to redefine the unit of measurement.

Metal cylinder used as 1-kg standard prone to deterioration, scientists fear

A replica of the prototype of the kilogram at the Cité des Sciences et de l’Industrie science museum in Paris, France. (Japs88/Wikimedia Commons, licensed under CC BY-SA 3.0)

Locked away in a vault in France is the shiny metal cylinder that, for 129 years, has been the standard against which all other kilograms are measured.

It's a heavy responsibility. The weight has been used to calibrate all scales, from those used to weigh tonnes of steel to micrograms of medicine.

But decades of dust, cleaning and even air pollutants have taken their toll, and the original kilogram is starting to show signs of deterioration, raising doubts about its accuracy.

This week, scientists from around the world are meeting in the Palace of Versailles to vote on whether to bring in a new measuring system that doesn't necessarily rely on a man-made object.

Alan Steele, Canada's chief metrologist and director general of the National Research Council's Metrology Research Centre, will weigh in on Canada's behalf.

Speaking by phone from Versailles on Tuesday, he said that while artifact standards like the original kilogram are convenient and have been around for a long time, their precision can diminish over time.

'A more scientific definition'

Alan Steele, Canada's chief metrologist and director general of the National Research Council's Metrology Research Centre, is voting on Canada's behalf. (National Research Council)

"It's so precious, and if you would scratch it or if it would change its mass because you're using it, that would be really catastrophic because you would be changing the definition and you would make changes to all the masses that you would weigh against that artifact," Steele told CBC Radio's Ottawa Morning.

"Now it's time to move to a more scientific definition [of a kilogram], one that uses equations from physics, and away from an old-fashioned artifact standard."

The one-kilogram cylinder stored in France is so precious that it's only been measured four times in its history. There are only one or two people in the world trained to handle it.

Instead, the new kilogram would be defined by a tiny but immutable fundamental value called the Planck constant.

An apparatus called the Kibble balance uses the Planck constant to measure the mass of an object using a precisely measured electromagnetic force.

'No one will notice'

The change wouldn't affect the way shoppers weigh produce at the grocery store, but it would have big implications for the tiny measurements scientists and high-tech manufacturers rely upon.

"A pound of butter will still be a pound of butter, a kilogram of sugar will still weigh a kilogram," Steele said.

"But in the future, as we start making more and more products that are small — like in pharmaceuticals or in quantum technologies or nanotechnologies — when you start using a calibrated kilogram that starts off at a really large value like one full kilogram and you calibrate all the way down to tiny masses like a microgram ... the uncertainty gets bigger and bigger and bigger.

"In the future, with the electronic kilogram realization, we'll be able to produce the unit of mass right at the size value that we need for our purpose, and that will enable us to make precision measurements in all the new technologies, and I think that's really quite exciting."

Even if the new system is approved, Steele hopes he can one day get the chance to see the original artifact.

"Maybe I'm hopeful that after it's put aside and it takes its place in history ... maybe people like me will actually have a chance to look at it."

CBC Radio's Ottawa Morning