Abstract Black holes occur when matter collapses inward. So what keeps matter apart? Without this simple fact—that atoms repel each other—all matter would collapse, and there would be no life. The reason that matter stays apart is due to the Pauli principle, named after physicist Wolfgang Pauli. It is a principle of quantum mechanics. However, the basis for this physical “law” is not understood. It just is. Without it, life in our universe would not be possible. This chapter discusses the basics of quantum physics in simple language along with boxes about the physicists who formulated this theory. The goal is to help the reader understand that quantum physics is another balance point in the existence of life.