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If you ask the Internet, the SI (metric) system is just obviously superior to the US customary (so-called Imperial) system of measures. After all, the rest of the world uses it; the US is the only real holdout. If us dumb Americans would just switch over, everything would be so much better! (I mean, didn't you hear about that multi-million dollar spacecraft we lost because part of it used Imperial and the other part used metric?)

You've probably guessed by now that I'm not convinced by this argument. Well, I'm not. Not only would a change from US customary system be impractical and costly at this point (an argument metric devotees scoff at), I don't think it would be a genuine improvement outside of certain scientific and technical fields where the metric system is already well-established.

First, let me say that it's amusing to me that in any other domain of culture, the replacement of indigenous systems with a standard invented by Europeans a would be seen as an absolute travesty these days, and usually rightly so. In addition, the last time I checked, the metric system has only ever come to replace older ways of measuring through government force, and often it hasn't even accomplished that completely (many people in officially-metricized countries still use older units of measure informally).

That's the basic problem I have: older units of measure evolved to meet the needs of the people using them, while the metric system is based on what's just about the most arbitrary unit of measure imaginable.

Let me expand on the first point first: the US customary system of measure, and other traditional system of measure, are meant to be practical, approximate measures. You can get a sense for the length of your living room in feet by actually stepping along it. You can get a sense for the length of a piece of string in inches by using your thumb from tip to knuckle. If you need more precise measurement than that, you can get it, but oftentimes these methods are good enough.

The metric system, by contrast, is ultimately based entirely on the meter. This is its strength: all the units, whether or length, volume, or mass, are defined in terms of the meter and are thus easily convertible. One kilogram is (or was) the weight of one cubic meter of water. A liter is the volume of that kilogram of water. So if you want to know how much water you need to fill your x by y by z meter pool, the answer is x * y * z liters. Brilliant! This ease of conversion between different types of units is what makes the metric system so useful in science. I get it.

The thing is, the meter is also the weakest link in the system. It is currently defined as the distance light travels in a vacuum in 1/299,792,458th of a second. If that seems like an incredibly arbitrary way to define a unit of measure, it's because it's not the original definition. The original definition of a meter is 1/10,000,000th of the mean distance between the equator and the North Pole. Now, that definition would be very useful for navigation, so why was it changed it to the weird light-based equation? Because the original calculation of the mean distance from the equator to the North Pole was wrong. It was off by 0.02%. That adds up when you're talking about 10 million of them. However, the original length was already in widespread use, and it was impractical to change it (ahem), so they kept the length but changed the way it was defined--several times, in fact.

So the metric system, which was designed with science rather than everyday use in mind, is founded upon an incorrect calculation that has since been replaced with an arbitrary definition. This is the "more rational" system that we're all supposed to use for measuring carpet.

Snark aside, I admit the metric system still has two major advantages over the US customary system: (1) unit conversion is extremely simple, and (2) everybody else uses it.  But these should both be kept in perspective.

First, advantage (1) could be fulfilled by any system based around a single unit. You could start with the US foot and built an easily-convertible system around it--or better yet, let's use the pint. A pint of water is just about one pound in weight, so let's redefine the pound to be the weight of one pint of water at one atmosphere of pressure (this redefinition would have still been possible in the 1800's, before the US government officially defined customary measures; prior to that, the units had no official definition and varied a bit from place to place). That settles volume and weight, so let's get length. A cubic pint of water is just about 3 inches to a side. Redefine the foot so that measure's exact, and we'll create a new unit, the quarter-foot, or qfoot (or preferably something nicer), as 3 inches.

We thus have a system where 1 pound = 1 pint = 1 qfoot^3. Measures that need to be exact can be done in megaqfeet, kilopints, centipounds, etc, while leaving the traditional conversions for "legacy units" like ounces, miles, etc. A decimalized, easily-convertible system that fits with the natural system that we're always using. 

Now that established the reasoning. In the last bit, we'll tie this into natural constants by working backwards. One foot is about the distance traversed by light in a vacuum in 1/1,000,000,000th of a second. Let's work backwards through the reasoning by first establishing 1 qfoot = distance traveled by light in a vaccuum in 1/4,000,000,000th of second. By establishing this length, we can then tweak the definition of pint and pound to keep the equation above, but now based on natural constants.

Now this system has all the theoretical advantages of the metric system without throwing the baby of traditional units out with the bathwater of poor convertibility. Of course, I have no hope of this system being adopted anywhere, especially outside of the US. It would be too impractical and costly to change now.

As for advantage (2), I would first point out that the world has gotten along OK dealing so far in its dealings with the US, and that trade got on well enough in the past when there was no international standard at all. There are and were problems, but they've been manageable. More to the point, this advantage is only an advantage given a globalized economy that at present is based on an unsustainable consumption of resources. As the Long Descent sets in, this economy is going to unwind and trade between distant nations will be minimal for quite some time. As the next technic societies begin to rise, a global economy might become an option again, but it'll be up to them to decide how to deal with it.

A deeper point for me is that metric advocacy seems to be a far more emotional topic than it needs to be. Some of it is simply a chance for non-Americans to score points against the juggernaut that is American culture and the American economy, I'm sure. But the connection of the metric system to science suggests to me that it has become a kind of shibboleth for the religion of progress; anyone who prefers a traditional system of measure to the rational, scientific metric system is an unintelligent troglodyte who is retarding Progress(tm).

As the religion of Progress, and industrial civilization, implodes-- the one in the face of broken promises, the other in the face of resource constraints and climate chaos--I suspect the cultures that succeed us will return to more pragmatic, informal units of measure. Not officially; just as the US customary system has its roots in the Roman Empire, the metric system may continue to be the system of a better time. But among the less-educated, less-literate folks, more immediately practical, approximate systems of measure could easily come to dominate. Time will tell.

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James Jensen

September 2017

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