The universe began as a very hot, extremely dense concentration of matter and radiation. A skeptic might ask "Is this a scientific statement, or one based upon belief?" Then the universe began to cool off and dilute itself by creating space into which it expanded. "But," the skeptic continues, "isn't this 'big bang theory ' just a guess, the consensus of unimaginative scientists? After all, nobody was around to see any of this happen."

Creation of evidence, however, does not require an observer. So the scientific question is what does the evidence of stars, galaxies, clusters of galaxies, black holes, quasars, and all other energy forms in the universe tell us about the beginning of the universe and its evolution? You will discover that what is true in the investigation of a crime is also true in the investigation of the universe, namely that the evidence severly constricts possible theories of how a sequence of events transpired.

Cosmology is the scientific study of how the universe began and evolved, and the people who do this work are called cosmologists. What is the scientific evidence that the opening statements are true? Keep in mind three important pieces of scientific evidence:

Expansion of the universe

Cosmic Microwave Background

Abundance of helium