Without the theorem of the excluded middle, all kinds of difficulties arise. In fact, many mathematical proofs are based on ...

A length? Infinity is bigger than the biggest number. Infinity is bigger than anything we can think of. Now infinity seems to be a type of size. Or is it something more abstract: a number, which we ...

Mathematicians define “infinity” very strictly. But we’ll stick with a broader, everyday definition: Infinity covers any number that isn’t finite.

—It's infinity, too. —But how do I write the number infinity? —It's like an eight lying down. —Is that even a number, like one or two? The point is, infinity is more an idea than a number.