Here in America, we measure height and weight in inches and pounds. Twelve inches make a foot, three feet make a yard, and there are 1,760 yards in a mile. That makes perfect sense, right? It makes so much sense, I just had to Google how many yards there are in a mile, because really, does anyone know that? The rest of the world, on the other hand, uses the metric system, which makes way more sense. It’s about to make slightly more sense; they’re changing it in 2018.
How many centimeters in a meter? One hundred. How many meters in a kilometer? One thousand. How many grams are there in one kilogram? Also one thousand. It’s beautiful in its simplicity. Water freezes at zero degrees, and boils at one hundred. In Fahrenheit, in addition to being impossible to spell, water freezes at 32 and boils at 212. Why? There’s a legend that it’s because Daniel Gabriel Fahrenheit was from Northern Europe, so he thought zero degrees should be when it’s too cold to be outside, not a warm day in winter. It may be apocryphal, but I still like it.
In engineering school I learned both, which honestly makes me wish America would swallow its pride* and switch systems. Let me tell you, after living in a country that only uses the metric system, I can promise you it makes life so much easier. At least our two countries count time the same way; or I would have showed up a week late for my job in France. Time zones are hard enough for me to keep track of.
But where do these measurements come from? In the Bible they use a cubit, which is the length of a forearm. This is the same basis for a foot, obviously. An inch is the length of a man’s finger, and a yard is about a stride. These all have the same problem of: whose foot or hand? If I owe the king a thousand bags of wheat a year, I would rather know how heavy he defines a “bag,” so I don’t get my head cut off. Luckily, these were all defined in 1959.
The meter (or “metre,” if you’re anywhere other than America) has a much more scientific basis, and hilariously, we have the French Revolution to thank for it. Being somewhat based in Enlightenment philosophy, the post-monarchical government became obsessed with making everything as logical as possible. To them, this meant making everything divisible by ten. If I were in charge of the revolution this would not be my first step, but alas, I was not. In my revolution, I like to think a lot fewer people would have been violently decapitated, but I digress.
My favorite example of logic-ing was the invention of their new calendar. It had 12 months, which means they had already failed to make everything base 10. Each month consisted of three weeks which were each 10 days long, but for this to work, they needed to add extra days at the end of the year. Sigh. Their days made slightly more sense. Every day was 10 hours, made up of one hundred minutes, each of which was one hundred seconds. Needless to say, this didn’t stick around too long, although really I’m impressed by its 12 year run.
The meter, however, did stick around. The Revolution-happy French defined it to be one ten-millionth of the distance from the North Pole to the equator. Later, in 1983, whoever is in charge of such things redefined it to be based on the distance light travels in a certain amount of time, but this was very close to the original length. The speed of light is an example of a universal constant, which means that no matter where you go in the universe, it will always be 299,792,458 meters per second. This number is ugly because the meter was defined, then the speed of light was defined, then the meter was redefined.
So the meter has already been redefined, and a cool thing about the metric system is that a lot of other constants are based on the meter. For example; a gram is exactly the weight of a cubic centimeter of water at four degrees Celsius. In theory, we could use the new meter to define everything related, but this is somewhat clunky. Instead, those in charge have elected to redefine everything based on universal constants. In 2018, a kilogram will still be the same ratio to the meter, but it will also be defined by the Planck Constant. The main seven units in the metric system are: meters, seconds, kilograms, moles, candelas, kelvins, and amperes. These seven units are all related in a very complicated rock-paper-scissors fashion which I will not even try to explain, so here’s a pretty picture.
These changes may seem arbitrary, but the one-millionth of a percent difference matters when you are trying to calibrate very sensitive machines, like in pharmaceuticals. On the other side of the size spectrum, these new super-duper exact measurements scale up to more precise numbers when measuring the size of galaxies.
But don’t worry; when we change the metric system in 2018, your eight ounces of fro-yo with extra strawberries won’t be any more absurdly expensive than it already is.