How can we say the universe is flat if it has depth? It may have very thin depth but it would mean that our universe is a rectangular cube, right? Also If we were to theoretically go in a spaceship towards the ends of our fast universe, what then? Will there be powerful particles to halt us from leaving the universe? And what would lie directly outside the universe? Is it just empty space until we reach the next universes? Can we actually leave our universe? Let us say we manage to leave the universe and we are in empty space. Would we be able to enter another universe if it is a sphere or would we be closed off? What about if it was a saddle universe? Or perhaps even a different shape universe is possible considering the different laws of physics.