The Big K

Photo by Ketut Subiyanto

Mornings are hard enough without stepping on the bathroom scales. Bleary-eyed and buck naked, I dutifully weigh myself before stepping into the shower. The digital verdict is either a cause for rejoicing or re-doubling my efforts to eat healthily. Either way, it becomes the basis for my breakfast choices – steel-cut oats or a nice seafood omelet.

Later, while sipping my coffee, I read an article about “Le Grand K” – the former international standard of weight for the kilogram.

For more than a century, the kilogram (kg) — the fundamental unit of mass in the International System of Units (SI) — was defined as exactly equal to the mass of a small polished cylinder, cast in 1879 of platinum and iridium.

Kept in a triple-locked vault on the outskirts of Paris, the platinum-iridium cylinder was officially called the International Prototype of the Kilogram (IPK). It even had a nickname: Le Grand K (The Big K). The accuracy of every measurement of mass or weight worldwide, whether in pounds and ounces or milligrams and metric tons, depended on how closely the reference masses used in those measurements could be linked to the mass of the IPK.[1]

Imagine, even the dreaded scale in my bathroom was calibrated through a chain of comparisons to The Big K in France, but scientists discovered a problem. Over the years, the standard has lost weight! No one was sure how it happened.

Over the past century, the trend for most sister copies [of Le Grand K] has been to gain mass relative to the original by varying amounts, although these amounts are unimaginably tiny. On average, the gain is around 50 micrograms (millionths of a gram) over 100 years. It’s possible, of course, that the original was losing mass relative to its copies or that it’s a combination of both. Either way, it’s no great cause for concern for most of us, as the change in mass is roughly the weight of a fly’s wing. [2]

But think what that means! “I can’t trust those scales!” I cried. Jan, who always seems to be one step ahead of me, replied. “John, Le Grand K, no longer defines the kilogram.” So she turned her laptop around and continued reading:

Rather than rely on a platinum cylinder in a bell jar in Paris, eggheads in the world of measurements decided to anchor the future kilogram to Planck’s constant. This is a fixed quantity tied in with E=MC2 and quantum theory, specifying the amount of energy carried by a single particle of light, or photon. And that’s just the most extremely simplified version.

Then I guess I’ll have to trust my scales and learn to enjoy oatmeal for breakfast, but it does point out how important standards are. Jim L. Wilson writes:

Even the best human measurements fall short, but it is not so with God’s Word. It is an unchanging standard. [3]

Amen! Now pass the jelly for my toast. I’m in the mood to celebrate.

[1] https://www.nist.gov/si-redefinition/kilogram

[2] https://www.atlasobscura.com/places/le-grand-k

[3] Wilson, J. L., & Russell, R. (2015). The Changing Standard of Le Grand K.

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