Consider for a moment the importance of standards of measure. In trade, in construction, in manufacturing, in virtually all aspects of life, things get measured. Doors and windows in houses are supposed to conform to standard sizes (a door is 80 inches tall here in the US), produce is sold at the market by the pound, time in minutes and seconds that everyone agrees upon, etc., etc., etc. It wasn’t always thus, however. Distance was measured in strides or, literally, feet and it depended on who was doing the walking what the figure would be. Standards had to be introduced to ensure fair trade and accurate construction, if nothing else. These standards were produced and literally crafted into physical form. Of the 7 units of measure that were defined by crafted objects – artifacts, as they’re called – only 1 remains today. The kilogram is defined by a metal cylinder kept under lock and key at various locations around the world, the “prime” object being held in a vault in France.
After 130 years of being the standard, the US’s National Institute of Standards and Technology (NIST) is saying that the kilogram is actually losing weight and it’s time to get a new standard.
The precise weight of the kilogram is based on a platinum-iridium cylinder manufactured 130 years ago; it’s kept in a vault in France at the International Bureau of Weights and Measures. Forty of the units were manufactured at the time, to standardize the measure of weight.
But due to material degradation and the effects of quantum physics, the weight of those blocks has changed over time. That’s right, the kilogram no longer weighs 1 kilogram, according to the National Institute of Standards and Technology (NIST). And it’s time to move to a different standard anyway.
Science has found ways to quantify all the other base units in terms of mathematical constants — the kilogram is the only material “artifact” still left in the current system of units, NIST points out. And strangely enough, it affects three of the base units of measure — the mole, ampere and candela. They’re are all linked to the weight of those 40 blocks of platinum-iridium.
There was once an official “meter stick,” a bar of the same platinum-iridium material with 2 marks on it that defined the distance. The measurement was re-determined by using a wavelength of light from krypton atoms, something that any lab with the right gear could reproduce on demand. That’s what they’re looking to do for the kilogram as well: find some constant that can be generated in a lab whenever needed.
I think this is a good move and, frankly, long overdue. It won’t mean a whole lot to most of us who really don’t care how the standard is presented, only that it’s accurate and, well, standard. But it’ll be good for our science efforts and who knows when that level of precision in measure might come in handy.