Astronomy 120 Discussion Questions: Cosmic Microwave Background, Big Bang Nucleosynthesis Name: 1. Radio astronomers Penzias and Wilson observed a \cosmic background" of microwave pho- tons. Explain how the Big Bang Theory accounts for these observations. 2. Give an observational argument for asserting that the microwave background comes from deep space. How do we know, for instance, that this radiation does not come from the Earth's atmosphere or from the Milky Way Galaxy? 3. What does it mean that the universe \became transparent" 300,000 years after the big bang? 1 4. In the early 1990's Full-sky maps of the Cosmic Microwave Background were constructed from observations by the COBE satellite. (a) In Figure 1(a) and Figure 1(b), the blackbody spectrum and the raw full-sky distribution of the CMB temperature is shown. Briefly explain where this radiation comes from, (a) CMB spectrum (b) CMB Distribution in Sky Figure 1: The Cosmic Microwave Background according to the Big Bang theory and explain how the Steady State theory fails to account for what is seen. (b) In Figure 2 the average temperature has been subtracted, leaving the small variations about the average. In this image, a large dipole anisotropy exists, with a hot spot in one direction, and a cool spot in the opposite direction. Explain how this anisotropy comes about. 2 Figure 2: Temperature of the CMB with the average temperature septracted (c) When the average temperature, dipole anisotropy and radiation from the Milky Way have been subtracted, we are left with a map showing true variations in temperature (fluctuations) in the microwave background, as shown by Figure 3. These variations are less then 0.0001 of a degree. What do these fluctuations imply about the universe at the time the cosmic microwave background was generated? Discuss the importance of these variations and the connection to the present-day universe. Figure 3: True fluctuations in the CMB (average temperature, dipole anisotropy and Milky Way emission subtracted) 5. What does \Big Bang Nucleosynthesis" refer to? What prediction is made by this part of the theory? What measurements can we make to test this prediction? 3 6. Why are there essentially no elements heavier than Lithium created in the early universe? Why can these heavier elements be formed in stars? 4.