ABSTRACT
The universe universe has existed for only 13.8 billion years. This chapter discusses the beginning of the universe (the big bang), the ensuing expansion, and the relationship between the shape of the universe and the matter it contains. The chapter is organized around the following questions:
What do we know about the universe?
In what sense is the universe expanding?
How is the density of matter related to the curvature of space?
Is the universe closed or open? In other words, is space finite or infinite?
What came before the big bang?
