Cosmic microwave background
Weinberg attempts to explain the early stages of the Universe after the Big Bang. Early in the book, Weinberg explores the origins and implications of the Hubble constant and addresses the evidence collected for the expansion of the Universe. He then tells the story behind the discovery of the Cosmic microwave background. After giving the reader a basis of understanding of astrophysics and particle physics, in chapter 5, Weinberg lays out the makeup of the Universe after its origin in a series of frozen frames.