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The definition of a kilogram, a unit roughly equal to 2.2 pounds, has changed forever.
Since 1889, the kilogram has been defined by a platinum-iridium alloy cylinder nicknamed Le Grand K, which is located in a triple-locked vault underneath the Pavillon de Breteuil, a building near Paris first unveiled by King Louis XIV in 1672.
But on Monday—World Metrology Day—Le Grand K lost its special status as the international prototype kilogram (IPK) and it will no longer represent this base unit of mass to the world.
From now on, the kilogram—along with the ampere, kelvin, mole, and candela—will be defined by fundamental physical and atomic properties instead of tangible human-made objects.
“The Metric System was envisioned to be ‘for all people for all time,’” said Barry Inglis, president of the International Committee for Weights and Measures, in a statement. “From its outset it sought to ensure long-term stability by defining the units in terms of an internationally agreed ‘constants of nature’ instead of an arbitrary reference.”
To that end, the “arbitrary” Le Grand K has been deposed by the Planck constant, a fundamental quantity related to the energy of photons, the elementary particles that make up light. Defined as 6.626 x 10−34 joule-seconds, the constant fixes the kilogram to the speed of light and a temporal unit of measurement—the second.
Read more here. (Vice)
Since 1889, the kilogram has been defined by a platinum-iridium alloy cylinder nicknamed Le Grand K, which is located in a triple-locked vault underneath the Pavillon de Breteuil, a building near Paris first unveiled by King Louis XIV in 1672.
But on Monday—World Metrology Day—Le Grand K lost its special status as the international prototype kilogram (IPK) and it will no longer represent this base unit of mass to the world.
From now on, the kilogram—along with the ampere, kelvin, mole, and candela—will be defined by fundamental physical and atomic properties instead of tangible human-made objects.
“The Metric System was envisioned to be ‘for all people for all time,’” said Barry Inglis, president of the International Committee for Weights and Measures, in a statement. “From its outset it sought to ensure long-term stability by defining the units in terms of an internationally agreed ‘constants of nature’ instead of an arbitrary reference.”
To that end, the “arbitrary” Le Grand K has been deposed by the Planck constant, a fundamental quantity related to the energy of photons, the elementary particles that make up light. Defined as 6.626 x 10−34 joule-seconds, the constant fixes the kilogram to the speed of light and a temporal unit of measurement—the second.
Read more here. (Vice)
