Objectives: Cosmology

Chapter Objectives: Cosmology is the study of the Universe as a whole, as one single object - the ultimate "Big Picture". The Cosmological Principle, which states that on the large scale the Universe is homogeneous and isotropic, is the starting point for this branch of astronomy. In this chapter we will see how the expansion of the Universe (as evidenced by the galactic red shifts) and the application of Einstein's General Theory of Relativity lead naturally to a big bang beginning to our Universe. The possibilities for the ultimate fate of our Universe, whether the expansion will continue forever or rather be stopped and a resulting big crunch will occur, will be explored. The gravitational lensing that is a consequence of Einstein's view of gravity will be described and illustrated and its utility in finding the elusive dark matter that may seal our Universe's fate will be demonstrated.

The Hubble expansion of the Universe and the cosmic microwave background radiation are the two most important pieces of observable data concerning the Universe as a whole. We will see how scientists apply these facts and the ideas of elementary particle physics to the first few seconds and minutes of our Universe's history. The few elementary particles (and antiparticles) that could exist in the extremely hot and dense early Universe will be introduced. The important changes that occurred in the early Universe as the temperature and density decreased will be explained. The inflationary versions of the big bang and the additional questions they answer will be discussed. The formation of large scale structure from a relatively smooth early universe in either a top-down or bottom-up scenario will be explored. The necessity for formulating a quantum version of gravity to understand the first small fraction of a second in our Universe's history will be described.

Chapter Skills: After studying this chapter you should be able to

  1. State the definition of cosmology and the "big questions" it asks.
  2. Give the basic tenet of modern cosmology.
  3. Use a two dimensional analogy to show how we can say our expanding Universe has no center.
  4. Describe the different types of geometry possible for our Universe and their relationship to mass.
  5. State the Cosmological Principle and its implications.
  6. Discuss the possible fates of the Universe and the related geometries.
  7. Describe what is known concerning gamma ray bursts and the suggested causes for these energy bursts.
  8. Distinguish between the "observable Universe" that we can now see and the entire Universe.
  9. Explain why the early Universe was radiation dominated and how it became a matter dominated Universe.
  10. List the "cast of characters" that were the participants in the Universe one millionth of a second after the Big Bang.
  11. Outline the events of the first three minutes of the Universe's history.
  12. Show how the Steady State was ruled out by observations concerning the Universe.
  13. Describe the observed properties of the cosmic background radiation.
  14. Explain how the cosmic background radiation is a natural consequence of the Big Bang and thus is the strongest piece of evidence in support of the Big Bang model.
  15. Show how the idea of Cosmic Inflation can eliminate the problems associated with the hot Big Bang theory.
  16. Distinguish between "Top Down" and "Bottom Up" theories of the formation of the large scale structure of the Universe.
  17. Briefly discuss the Planck scale and the need for a quantum view of gravity to understand the earliest era in our Universe's history.