The Weight is Over, The Kilogram is Settled
Metrology is the study of weights. A scientist who studies metrology is called a metrologist. Metrologists, physicists, and other specialists, for decades, have been trying to tackle an issue concerning the mass of a kilogram. When you think about it for a second, this is a rather significant undertaking since the kilogram is the international standard by which all mass in the universe is measured.
The kilogram is not just a concept, theory, or arbitrary measurement. It is based on an actual physical object – a platinum and iridium cylinder that, for 126 years, has defined the kilogram from a high-security vault outside Paris. Like all objects over time, they slowly shed mass, and since 1889, the actual mass of the object has diminished by 60 micrograms. This is a problem the scientific community has been aware of for a very long time.
Gathering last week in Paris, the 104th meeting of the International Committee for Weights and Measurements (CIPM) was satisfied that after years of experiment it has found a new method to define the kilogram. As reported by Nature magazine:
The breakthrough comes in time for the kilogram to be included in a broader redefinition of units — including the ampere, mole and kelvin — scheduled for 2018. And this week, the International Committee for Weights and Measures will meet in Paris to thrash out the next steps.
Research teams, using two completely different methods, achieved results that are both precise enough, and in sufficient agreement, to topple the physical definition. One was to manufacture near-perfect spheres of silicon crystal and literally to count the atoms using X-ray diffraction. The other was to develop an insanely accurate electromagnetic scale (a watt balance) and from the electric charge measured reverse ferret via Planck’s constant to Avogadro’s number.
The agreement will lend stability to the measurement of a kilogram, and no longer will we have to base the international measurement on a decaying object.
The metric system now encompasses seven base units: mass (kilogram), distance (metre), time (seconds), electric current (ampere), temperature (Kelvin), substance (mol) and luminosity (candela). Of those seven, six are based on universal constants of nature. The kilogram had been the last holdout.
Correction: Kilogram is a measurement of mass, not weight as was originally posted.