Erno Rubik was not trying to invent a toy. In 1974, the Budapest architecture and interior design professor wanted to solve a structural riddle: how can many small parts rotate independently without the whole object falling apart? His answer was a hidden central cross with center squares fixed to it and edge and corner pieces riding on internal tracks. Then he twisted his prototype, scrambled it, and spent a month trapped by his own creation.

This episode follows the cube from wooden blocks held by rubber bands to a 1975 Hungarian patent, a chance encounter at the 1979 Nuremberg Toy Fair, and the Ideal Toys deal that renamed the Magic Cube after its inventor. We cover the 1980s craze, the bestselling solution books, the crash, the speedcubing revival, and the mathematics of 43 quintillion permutations and God's number.

• Why the po ...