I've learned now that when thinking about questions like this one you take a close look at that sign on the door which says, "Abandon common sense all ye who enter here!" In fact I quite like Einstein when he said that common sense is the collection of predudices we acquire before we are 18 years old.
Having said that, I have trouble in understanding how the universe can be infinite. It started off very small. It expanded. The latest evidence indicates that it is currently expanding. So in what sense can it be infinite?