The Sizes of Infinity

Infinity is a confusing and often misapplied concept. This TED talk -- pointed to by Maggie Koerth-Baker in her post on the problem some fundamentalist Christians seem to have with set theory -- does a great job of sorting out the issues on the sizes of infinities as well as explaining why the continuum hypothesis is necessarily unsolvable. (NB: I don't think it defines the continuum hypothesis as well as it might or points out that its non-provability and disprovability depend on the consistency of the Zermelo-Fraenkel Set Theory with Axioms of Choice, but those are not important concerns.)