How can the universe be finite?
It most likely is since energy and matter cannot be created or destroyed.
Easiest way to explain it is to look at the big bang. If the universe started with a super hot, super dense bit of matter (say the size of a sugar cube) it has to have very specific margins. 1 second after the big bang the rapidly expanding universe still has to have very specific margins. And since the matter was a definite mass and did not have infinite energy, which is not possible, the universe, although vast, cannot be infinite.