The universe is infinite in size. All the theories about a warped universe are wrong. From where you are standing, hold a yard stick and pick any direction including up/down and imagine traveling out into the universe along a STRAIGHT line parallel to the yard stick. Let's say (just for fun) that you could travel at the speed of light. You will NEVER / EVER come to the end of the universe because there is no end. And forget about coming back to where you started. I am talking about a straight line PARALLEL to the yard stick at the starting point. Forget about the line eventually bending because again, you are always traveling straight relative to the yardstick.