The generation ship — a space ship that takes multiple generations to reach its destination — is a classic science-fiction concept that raises the question of designing society for posterity:
We humans are really bad at designing institutions that outlast the life expectancy of a single human being. The average democratically elected administration lasts 3-8 years; public corporations last 30 years; the Leninist project lasted 70 years (and went off the rails after a decade). The Catholic Church, the Japanese monarchy, and a few other institutions have lasted more than a millennium, but they’re all almost unrecognizably different.
(Hat tip to Michael Nielsen.)