Apathy Sketchpad

An article in American Scientist the other day raised a topic I’ve thought about before. (In fact, it proposes an idea I’ve had before, which should give you some idea how revolutionary it isn’t.) Essentially, the idea is to so away with a thing called “Le Gran K”, which is not a breakfast cereal but is in fact a little metal object roughly the size and shape of a dimmer switch, which rather scarily weighs exactly a kilogram. (It’s also called “Le Grand Kilo”, but that sounded less like a cereal.) It’s scary because something that size has no business at all weighing anything like that much, but mostly because it’s rubbish.

I mean, it is, for all that it’s kept securely in a sealed container in a sealed container in a vault in a basement in France, still nothing more than a lump of metal. The old metre prototype was done away with in 1960 (and was made of the same stuff as Le Grand Kilo, so imagine how much it must weigh). Nobody’s really managed to build a Platinum-Iridium prototype for the second yet, but the point is that the other base units are all defined by properties of the universe, and not properties of French paperweights.

The idea for the kilogram, at least the one doing the rounds on the Internet this week, is to simply fix Avogadro’s number — to the layman, Avogadro’s number is the number of hydrogen atoms in a gram of hydrogen — and hence define the gram as the weight of that many hydrogen atoms. (Actually, the definitions use Carbon-12, and using other things messes it up because apparently if you split up an atom and weigh the parts they won’t add up to the weight of the original atom. Nuclear, eh? What’s it good for?)

In case you’re interested, the kilogram is the base unit, not the gram. According to Wikipedia, this is because of the French Revolution. Which makes as much sense as anything else, I suppose.

Anyway. There are a few other far more complicated proposals, and really the only advantage they have over this idea is that they end up with a kilogram slightly closer to the one we currently use. We’re talking millionths of a percent here. Other than that all the ideas are much the same, as far as I can tell. But the fact that this one is so ludicrously simple — a kilogram is the weight of 50,184,511,755,867,423,674,922,666-and-two-thirds unbound atoms of carbon 12 in the ground state (alright, point taken, but I still just defined it in one sentence) — makes it far more useful.

Really, simplicity isn’t the key so much as how easy it is to determine experimentally. In order to adopt a definition for a unit like a kilogram, we really need to know exactly what that definition is in some practical terms we can understand (unless you fancy counting out six hundred thousand billion billion atoms). Luckily, the experiments we currently use to try to pinpoint Avogadro’s Number would suddenly become experiments to calibrate scales to the correct definition of the kilogram. Much the same is true of all the “pick a constant, fix it, and define the kilogram from there” ideas.

But the bottom line, to me, is that it doesn’t matter which we pick. I like the idea of fixing Avogadro’s Number, but really I just want rid of Le Grand Kilo. It’s pathetic. Whatever definition we pick will be closer to the current mass of Le Grand Kilo than the mass of Le Grand Kilo will be in a hundred years. It’s lost 50 milligrams already, and nobody knows where they’ve gone. And that means that the kilogram is a smaller unit now than it was in 1890, because of course Le Grand Kilo is still, by definition, exactly one kilogram. (The authors of the Scientific American article say “This implies that by current measurement conventions, the mass of a single atom of carbon-12 is changing in time, whereas modern theory postulates that it remain constant.” This is meaningless drivel.) At least, we think it’s lost 50 milligrams. It’s hard to say, partly because it still, by definition, has exactly as many milligrams as it had to begin with, but mostly because what the hell are we supposed to measure it against?

Once we get rid of this archaic and rather silly definition, the metric system will finally be a complete system. Won’t that be nice? Then we can really lord it over those monkeys still using pounds and ounces. Also, they can raise some cash by sticking Le Grand Kilo on eBay. Think how much that would get.