I find it convenient at the beginning of each semester to talk about physics in general, to give my students an overview of this great and glorious subject.
One theme of my general summary of physics are “the seven givens”, or basic building blocks of the Universe. They are space, time, mass, energy, force, charge, and momentum.
Regarding space, I always comment that it is problematic to talk about the size of the Universe (the one we live in), regardless of whether the Universe is finite in size, or infinite. Neither statement is appealing to our lizard brains, but I think the idea of an infinite Universe is the worse of the two. There is something inherently meaningless about an infinitely sized Universe.
In this numberphile video, Cantor’s original ideas about the types of infinities are explored in a surprisingly satisfying way.