[powderhorn]

... if it's infinite, it can't "expand," and if it's expanding, what is it expanding into?

It's not infinite. There is a theoretical end to the known universe.

It is expanding like a balloon expands, everything goes farther out, and individual galaxies move farther away from each other as the universe expands. The essential qualities of space include: gravity, the strong force, the weak force and electromagnatism. Without these forces, time and space cannot exist.

[Henchster]

"It's not infinite. There is a theoretical end to the known universe."

So what's on the other side? You know, the "non-universe" side?