## Our Weigh or the Highway

On the outskirts of Paris, in a triple-sealed chamber, sits a golf-ball sized cylinder made of platinum and iridium. It’s officially known as the International Prototype of the Kilogram — or IPK, for short — but locals refer to it as Le Grand K.

The International Prototype of the Kilogram (IPK), known colloquially as Le Grand K, is protected by three vacuum-sealed bell jars.

Cast in 1879, the IPK serves as the international standard for mass. For a century-and-a-half, the accuracy of any weight measurement was linked to this very precisely hewn hunk of metal.

The kilogram is the only unit still defined in terms of a manufactured object, and that’s shaky and solitary ground on which to rest. In 1960, the only other SI unit still based on a physical artifact — the meter — was redefined in terms of the wavelength of light from a specified source, linking it to natural phenomena.

But no longer.

Today, Le Grand K will be retired when representatives from 60 countries will meet in Versailles to approve a new definition of the kilogram. Officially, the change won’t take place until May 20, 2019, which means that for a short time, the IPK, Pete Sessions, and Claire McCaskill will occupy a similar state of lame-duck limbo.

And what is the new definition for the kilogram? It’s pretty straightforward…

The kilogram (kg) will be defined by taking the fixed value of the Planck constant h to be 6.626 070 15 × 10−34 J⋅s. The unit J⋅s is joule-seconds, which is equal to kg⋅m2⋅s−1, where the meter and second are defined in terms of c, the speed of light, which is 299,792,458 meters per second (m⋅s−1), and ΔνCs, the ground state hyperfine splitting frequency of cesium-133, which is 9,192,631,770 Hz.

See? Easy peezy.

Over time, the IPK has, surprisingly, lost weight. And scientists can’t really explain why. The cylinder now weighs about 50 micrograms, or roughly the weight of an eyelash, less than it weighed in 1879. The irony, though, is that a kilogram, by definition, is equal to the weight of the IPK. So, technically, it isn’t that the kilogram has lost weight; in truth, the rest of the world has been getting a little heavier. (Keep this factoid in your back pocket for a few days. It is perhaps the best and most scientific excuse you’ll be able to offer if you don’t like the reading on your scale around the holidays.)

All this talk of Le Système International makes me think about the many important benchmark conversions that should be part of every science curriculum:

2000 mockingbirds = 2 kilomockingbirds

1012 microphones = 1 megaphone

10 cards = 1 decacards

1,000 grams of wet socks = 1 literhosen

And the most important benchmark, for when you need to convert between expatriate poets and televangelists:

And finally, if you’ve read this far, a PG-13 passage from Wild Thing by Josh Bazell:

In metric, one milliliter of water occupies one cubic centimeter, weighs one gram, and requires one calorie of energy to heat up by one degree centigrade — which is one percent of the difference between its freezing point and its boiling point. An amount of hydrogen weighing the same amount has exactly one mole of atoms in it. Whereas in the American system, the answer to “How much energy does it take to boil a room-temperature gallon of water?” is “Go fuck yourself,” because you can’t directly relate any of those quantities.

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• 1. Ian Kammann  |  November 16, 2018 at 11:28 pm

Wouldn’t it take 1 000 000 000 000 microphones to make a megaphone? ‘A million microphones’ will only get you a ‘supersystem’.

• 2. venneblock  |  November 19, 2018 at 11:25 am

Fail! Post updated. Thanks for the careful eye.

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