angels dancing on the head of a pin

Etymology
An allusion to the theological question “How many angels can dance on the head of a pin?” — a question cited to debunk mediaeval angelology in particular and scholasticism in general. The point is that explorative discussions that the discussants consider important can be academic in both senses of that word—not only arcane but also irrelevant.

Noun

 * 1)  The subject of arcane intellectual speculation; used as an example of a subject of enquiry in which the pursuit is of no value.

Translations

 * Finnish: neulan kärjellä tanssivat enkelit
 * French: sexe des anges, le sexe des anges,
 * Italian: il sesso degli angeli
 * Portuguese: sexo dos anjos, o sexo dos anjos
 * Spanish: el sexo de los ángeles