I have learned a lot about cosmology on this forum, but I’m still behind on the logic. So far I have understood that, since the universe is everything, it cannot have a center nor a boundary. But it does have an expansion and that’s when my problems start. I would like to concentrate on a couple of questions, in order to make some progress: - if we know the age of the universe and we know its rate of expansion, why is there so much discussion about its total size? - if the size of the universe is finite, how can the universe be isotropic? - assuming that the universe is flat and finite, how can it not have a boundary? I am not talking about the observable universe, I am talking about the total universe. Further, I am assuming that BBT refers to the total universe. .