Fun article! Two questions for you or your readers:

(1) do we think the size of our universe's 3D-balloon is dictated by the distribution of matter, e. g. is it getting bigger because matter has momentum, kind of stretching it? or is space itself been given a kick by the big bang?

(2) do we think it is curved into some 4D torus or such?

(3) If so, how rapidly is the length of a circumnavigating line expanding? Is it a constant speed, or perhaps it is a constant percentage (thus accelerating speed)?