Hello, friends! Welcome to another episode of Sciency Words, a special series here on Planet Pailly that’s all about those weird words scientists use. Today on Sciency Words, we’re talking about:
Yes, scientists use some very strange words. You know the kind of words I mean. Words that are hard to pronounce. Words with definitions that only make sense if you understand differential calculus. But you know what’s even weirder? When scientists take words you already know and redefine them. That’s what astronomers and astrophysicists have done to the word “metal.”
Approximately 75% of the matter in the universe is hydrogen. 24% of it is helium. And the remaining 1%? Ask an astrophysicist, and they’ll tell you the remaining 1% is all “metal.” If that seems weird to you, don’t worry. All the other scientists think it’s weird too.
For years now, I’ve been trying to figure out how this started. Who gets credit (or blame) for first messing up the definition of metal?
I don’t know, but I do have a pet theory. Perhaps certain chemical elements (like nickel or iron) are easier to detect in outer space than others. And if you’re trying to study that 1% of the material universe that isn’t hydrogen or helium, perhaps those easier-to-detect elements (which happen to be metals) serve as a convenient proxy for everything else—including nonmetals like nitrogen, carbon, and oxygen.
According to the Oxford English Dictionary Online, the earliest documented usage of either “metal” or “metallicity” (in the astronomy sense of those words) is this 1969 paper on the molecular composition of stars. Now I won’t pretend to have read the whole paper (it’s over 60 pages long), but based on what I did read, I can say this much: this cannot be the true first usage of the word metal (in the astronomy sense).
At one point, the authors, two astronomers from U.C. Berkley, categorize nitrogen as a metal. No explanation is offered. Clearly the authors expect their readers (i.e. other astronomers) to understand why nitrogen would be considered a metal, which suggests to me that most astronomers in 1969 already understood “metal” to mean “matter that isn’t hydrogen or helium.”
However, I can also say this: I think this paper supports my pet theory. The paper describes a new technique for determining the molecular composition of stars. In explaining this new technique, the authors focus on the spectroscopic signatures of three specific elements: sodium, magnesium, and calcium. Those three elements are then used as a proxy for all the other non-hydrogen and non-helium elements that might be found inside a star.
Sodium, magnesium, and calcium are all—wait, let me double check the periodic table—yes, all three of those elements lie on the metal side of the metalloid line. And thus through a process linguists call semantic generalization, the word metal is generalized to mean something more than it originally meant.
Next time on Planet Pailly, someone really wanted to pick a fight with me about life on Mars.