glass bead game

An activity or field of study so arcane and detached from, and with no application to, the real world that it is rendered absurd. E.g., theology, analytic/linguistic philosophy.

A waste of one's time.

Refers to the recondite game studied and played in the Herman Hesse novel, The Glass Bead Game.
Synonymous idiom: Ivory Tower

The theologians contemplating how many angels can fit on the head of a needle is mere glass bead game.

The study of astrology is a glass bead game.

Postmodernist philosophy is a glass bead game.

Don't waste my time with your Eco-feminist glass bead game.