Several days ago, University of Wisconsin Law School professor and frequent blogger Ann Althouse noted President Obama's use of the expression "hair on X," to mean that X is complicated," from David Remnick's recent New Yorker profile. Here are the two Obama quotes that she cites:
Because, if you're doing big, hard things, then there is going to be some hair on it — there's going to be some aspects of it that aren't clean and neat and immediately elicit applause from everybody.
Having said all that, those who argue that legalizing marijuana is a panacea and it solves all these social problems I think are probably overstating the case. There is a lot of hair on that policy. And the experiment that's going to be taking place in Colorado and Washington is going to be, I think, a challenge …
Althouse concluded that the phrase "came from the realm of business deals," after finding a 2010 Globe and Mail article about mergers and acquisitions (M&A) buzzwords with the following explanation of the term "hair":
"Hair" on a deal is often used to describe a business that has some negative aspects. For example, if you're trying to sell your company and you have one customer that generates 50 per cent of your revenue, you're being sued by a former employee and your customer records are spread in three disparate databases, buyers (or their advisers) may say your company has "a lot of hair on it."
However, physicists have been using a similar metaphor for at least 40 years. In the 1973 book Gravitation, theoretical physicist John Wheeler suggested that black holes have no "hair," now known as the no-hair theorem. As Wikipedia explains:
all black hole solutions of the Einstein-Maxwell equations of gravitation and electromagnetism in general relativity can be completely characterized by only three externally observable classical parameters: mass, electric charge, and angular momentum. All other information (for which "hair" is a metaphor) about the matter which formed a black hole or is falling into it, "disappears" behind the black-hole event horizon and is therefore permanently inaccessible to external observers.
I would argue that this physicists' sense of hair derives from an earlier hacker/engineering usage, summarized in the Jargon File entry for hair:
[back-formation from hairy] The complications that make something hairy. ... Often seen in the phrase infinite hair, which connotes extreme complexity.
In fact, I recall hearing this usage around MIT in 1965 or 1966. As the Jargon File suggests, the logical etymological predecessor to "hair on X" is the adjectival "hairy," which the Oxford English Dictionary traces back to British schoolboys in the mid-19th century and defines as such:
A.1.f. In various fig. and slang senses: difficult (quot. 1848); out-of-date, passé; frightening, hair-raising; crude, clumsy, rough, erratic.
It's possible that the M&A culture derived its use of "hair on X" independently from 19th-century schoolboy slang. But, pending evidence of such a history, I'm going with the theory that it arrived on Wall Street sometime in the 1990s with the advent of a new breed of "quants," analysts with a background in … you guessed it, physics, math, and engineering.
So how did hair=complexity come into Obama's lexicon? Again, pending evidence to the contrary, I'd suspect the general diffusion of engineering slang into the world of political operatives, some of whom now have a background in statistical modeling and computer science. Though I guess there might be enough back-and-forth between Wall Street and high-level politics to allow for some terminological flow from M&A jargon into political deal-making.