Canadians make weighty discovery
ADVANCE is considered a startling leap in redefining the metric system
Ateam of Canadian researchers has made a “startling” leap forward in the international quest to establish a new, hyper-precise measurement of the kilogram, an achievement it says has moved science “closer to a redefinition of the metric system used around the world.”
The investigative triumph took place in a special laboratory at the Ottawa-based National Research Council of Canada – the federal government’s main scientific agency – and has been detailed in the latest issue of the journal Metrologia, published by the global headquarters of physical science, Britain’s Institute of Physics.
The kilogram has long been defined by a single, man-made “international prototype” – a four-centimetre-tall cylinder of platinum — held by a Paris scientific institute, the ingot itself meant to represent the weight of one litre of water.
But the International Prototype Kilogram and its official clones at the NRC and other national labs are – in infinitesimal ways – imperfect. They can shed or accumulate atoms that, over the years, subtly throw off the accuracy of the very objects meant to be the gold standard for global measurements of mass.
In a world where advanced scientific research and various high-tech systems – from nanotechnology to satellite communication to global computer networks – increasingly rely on absolute precision in all timing, weights and measures, researchers have been driven to establish unerring and infinitely reproducible standards.
The metre, once based on a metal rod kept at the same Paris institute that possesses the IPK, has been officially redefined according to an immutable wavelength of light. And earlier this year, a contentious proposal to have “atomic” time – based on the special properties of the cesium atom – replace a system geared to the slightly irregular movements of the Earth, was seriously considered by a UN regulatory body, but ultimately deferred for more study.
Researchers in Canada and several other countries are now working to establish a new universal standard for measuring the kilogram based on two “fundamental constants of nature” – from physics, the so-called Planck constant, named for the Nobel-winning German scientist Max Planck and calculated from the energy signature of light particles; and from chemistry, the Avogadro constant, named for the 19th-century Italian molecular theorist Amedeo Avogadro and determined from the mass of a single silicon atom.
The Canadian breakthrough follows the NRC’S acquisition in 2009 of a so-called watt balance from the U.K.’S National Physical Laboratory, which pioneered the search for a Planck-based kilogram but recently refocused its research priorities.
One of only two such instruments in the world, the multimillion-dollar device now owned by the NRC is a kind of supercharged scale designed to yield the Earth’s most accurate measurements of mass.
But the Canadian team also is testing its watt balance calculations against separate Avogadro measurements based on the properties of a silvery, grapefruit-sized silicon sphere – chemistry’s purest embodiment of the kilogram – held by a German research institute.
And in a first for any single scientific body in the world, the NRC researchers completed measurements using the two different methods and produced almost identical results – the vanishingly small variance expressed as just “20 parts per billion,” according to the Metrologia paper.