Ninety percent or more of the matter in the universe is unseen. Nobody knows what it is. The universe expands, but nobody knows how long the expansion has been going on. Will it expand forever, or collapse in a Big Crunch, perhaps a Big Bang in reverse. From Aristotle to Newton, Einstein and Quantum Mechanics, Introducing The Universe recounts the revolutions in physics and astronomy which underlie the present-day scientific picture of the universe.