1. Chapter 18: Chapter 18: Cosmology

2. WHAT DO YOU THINK? What does the universe encompass? Is the universe expanding, fixed in size, or contracting? Will the universe last forever?

3. You will discover… cosmology, which seeks to explain how the universe began, how it evolves, and its fate the best theory we have for the evolution of the universe—the Big Bang how astronomers trace the emergence of matter and the formation of galaxies how astronomers explain the overall structure of the universe our understanding of the fate of the universe

4. Cosmological Redshift

5. Expanding Cake Analogy Just as all the chocolate chips move apart as the cake rises, all the superclusters of galaxies recede from each other as the universe expands.

6. Bell Labs Horn Antenna Arno Penzias (right) and Robert Wilson

7. In Search of Primordial Photons Wilkinson Microwave Anisotropy Probe (WMAP) satellite, launched in 2001

8. In Search of Primordial Photons The balloon-carried telescope BOOMERANG

9. Spectrum of the Cosmic Microwave Background

10. The Microwave Sky The Doppler shift across the sky is caused by the Earth’s motion through the microwave background.

11. Our Motion Through the Microwave Background Because of the Doppler effect, we detect shorter wavelengths in the microwave background and a higher temperature of radiation in that part of the sky toward which we are moving.

12. Unification of the Four Forces

13. Early History of the Universe

14. The Cause of Inflation

15. Observable Universe Before and After Inflation

16. Pair Production and Annihilation

17. Evolution of Density

18. Era of Recombination

19. Observable Universe The cosmic light horizon today is about 13.8 billion light-years away in all directions. Inset: This HST Deep Field Telescope image shows some of the most distant galaxies we have seen.

20. Structure of the Early Universe This Wilkinson Microwave Anisotropy Probe (WMAP) image shows temperature variations in the cosmic microwave background. Inset: Tiny temperature fluctuations, observed by BOOMERANG, are related to the large-scale structure of the universe today, indicating where superclusters and voids grew.

21. Galaxies Forming by Combining Smaller Units This painting indicates how astronomers visualize the burst of star formation that occurred within a few hundred million years after the Big Bang.

22. Galaxies Forming by Combining Smaller Units Hubble and Keck telescope images of two groups of stars that are believed to be protogalaxies, from which bigger galaxies grew

23. Galaxies Forming by Combining Smaller Units This Chandra X-ray telescope image shows gravitationally bound gas around the distant galaxy 3C 294. The X-ray emission from this gas is the signature of an extremely massive cluster of galaxies.

24. Stellar Birth Rates Star formation continued actively for billions of years when the universe was very young.

25. Stellar Birth Rates Most of the stars in an elliptical galaxy are created in a brief burst of star formation when the galaxy is very young. In spiral galaxies, stars form at a more leisurely pace that extends over billions of years.

26. Creation of Spiral and Elliptical Galaxies A galaxy begins as a huge cloud of primordial gas that collapses gravitationally.

27. A Cosmic Timeline

28. Possible Geometries of the Universe The curvature is either (a) Positive (b) Zero (c) negative

29. Cosmic Microwave Background and the Curvature of Space

30. Dimmer Distant Supernova These HST images show the galaxy in which the supernova SN 1997ff occurred. This supernova was dimmer than expected. The distance to it is greater than it would be if the universe had been continually slowing down. An outward force is acting over vast distances in the universe.

31. Dimmer Distant Supernova

32. WHAT DID YOU THINK? What is the universe? It is all the matter, energy, and spacetime that will ever be detectable from the Earth or that will ever affect us. Did the universe have a beginning? Yes, it occurred about 13.8 billion years ago in an event called the Big Bang. Will the universe last forever? Current observations support the belief that the universe will last forever.

33. Key Terms Big Bang closed universe confinement cosmic light horizon cosmic microwave background cosmological constant cosmological redshift cosmology dark ages dark energy decoupling era of recombination expanding universe grand unified theory (GUT) homogeneity horizon problem inflation inflationary epoch isotropy isotropy problem matter-dominated universe open universe pair production Planck era Planck time primordial fireball quark quintessence radiation-dominated universe strong nuclear force superstring universe weak nuclear force