Arguably the two greatest problems facing particle physicists, cosmologists, string theorists, and the like are both associated with an apparent failure of a notion called “naturalness”.  Until now, I’ve mostly avoided this term on this site, because to utter the word demands an extended explanation.  After all, how could nature be unnatural, by definition?

Well, the answer is that the word “natural” has multiple meanings.  The one that scientists are using in this context isn’t “having to do with nature” but rather “typical” or “as expected” or “generic”, as in, “naturally the baby started screaming when she bumped her head”, or “naturally it costs more to live near the city center”, or “I hadn’t worn those glasses in months, so naturally they were dusty.”  And unnatural is when the baby doesn’t scream, when the city center is cheap, and when the glasses are pristine. Usually, when something unnatural happens…