Scientists are redefining the kilogram

Divers weights, and divers measures, both of them are alike abomination to the LORD. Divers weights are an abomination unto the LORD; and a false balance is not good. Proverbs 20:10, 23 As Reported by Randy Boswell of Postmedia News, February 24, 2012:

A team 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 super-charged 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. "It's really exciting to see that convergence," said project leader Alan Steele, director of metrology — the science of measurement — at the federal agency. "Our results agree with themselves really well." The NPL, the British lab that build the watt balance and sold it to Canada, hailed the NRC's findings as a major advance in the quest for a better kilogram, issuing a statement that said the Canadian efforts "look set to provide considerably greater accuracy" in measuring the world's fundamental unit of mass. Depending on the outcome of further research aimed at resolving minute discrepancies between the Canadian results and recent data from the U.S. and Europe, the latest findings could herald "the start of the end for the physical kilogram," the British institute stated. Steele told Postmedia News on Friday that there's much more work to do. Even though Canada's measurements are converging toward a new definition of the kilo, NRC scientists are working closely with colleagues in the U.S. and Europe to try to identify the potential causes of the slight inconsistencies that remain between countries' calculations. The instruments involved in the experiments, said Steele, are so precise that the gravitational differences between labs on the first and second floors of a research centre — or even the presence of a large delivery truck nearby — could severely skew the measurements made by a watt balance, which require exceedingly careful calibrations and compensations. "We still have to understand why the Canadian results don't agree with some of the other results around the world," he noted. "We want not just the same answer, but the same right answer, using both the 'chemistry way' and the 'physics way.' The world will have the right answer when we have convergence of all of these things."

The original article Reconciling Planck constant determinations via watt balance and enriched-silicon measurements at NRC Canada was published in Metrologia 49:1, February 2012, pp. L8-L10.