Fall 2000 ASTR 1120-001 Review for Quiz 6

The quiz will contain 10 multiple-choice questions, and will be 10 minutes long. The intention is that all material on the quiz (saving matters of logic and common sense) is referred to somewhere here.

You can ask about the answers in the review session at 6-7pm on Monday 11 Dec in Duane G1B30 (our usual lecture hall).

  1. Observational Evidences. What are the principal evidences favoring the standard hot Big Bang theory of the Universe? What shows that the Universe is expanding? What shows that the Universe was once hot and dense?

  2. Cosmological Principle. What is the cosmological principle? What observational evidence favors the cosmological principle? Does the Universe have a center? Does it have an edge? What is the Universe expanding into?

  3. Geometry of the Universe. The cosmological principle restricts the spatial geometry of the Universe to one of just three possibilities - closed, flat, and open. What measurable differences do the three types have? Is the Universe finite or infinite in a closed/flat/open Universe? What is W? What does it have to do with the geometry of the Universe? What is the total value of W thought to be?

  4. Cosmic Scale Factor. What is the Cosmic Scale Factor? How big is it (trick question)? Sketch how the Cosmic Scale Factor varies with time in matter-dominated closed/flat/open Universes, and in a flat Universe containing matter and a cosmological constant. How does the wavelength, redshift, and temperature of photons vary with Cosmic Scale Factor? If we say that an object is at a redshift of z, what does it imply about how much smaller the Universe was then than now?

  5. Vacuum energy. What is meant by the Cosmological Constant? What is vacuum energy? Does vacuum energy gravitate, and if so, in what way? In January 1998 two separate teams reported that the Hubble diagram of high redshift Supernovae showed that the Universe was accelerating. What is the connection between this discovery and vacuum energy? Is there any difference between the vacuum now and the vacuum in the extremely early Universe (during inflation)?

  6. Horizon. The deeper we look in space, the further back in time we see. Why? What, where, and why is our horizon? What is meant by the edge of the observable Universe? What lies beyond the edge of the observable Universe? Does the Cosmic Background Radiation come from the horizon? What happens to our horizon as time goes by?

  7. Cosmic Microwave Background (CMB). For some of the remarkable history of the CMB, check Dick McCray's hypertext. What is the CMB? What kind of spectrum does the CMB have? What is its temperature? Has the CMB always been at the same temperature it is now? Why can we see no further back than the CMB? How does the Microwave Background vary around the sky? Why does the CMB appear slightly hotter in one half of the sky than the other half?

  8. Recombination Epoch. What is the Recombination Epoch? Recombination happened at a temperature of 3,000K. What has this temperature got to do with the ionization of hydrogen? What important things happened at Recombination? Why is an ionized gas more opaque than a neutral gas? What does it mean to say that the Cosmic Background Radiation comes to us from the Epoch of Recombination?

  9. Fluctuations in the CMB. What does the power spectrum of temperature fluctuations in the CMB mean? What can we learn from the power spectrum of fluctuations in the CMB? What is the connection between the horizon size at Recombination, and the position (harmonic number) of the first acoustic peak? How does this provide information about the geometry of the Universe? What results from the balloon-borne CMB experiments Boomerang and Maxima were reported in Spring 2000?

  10. Horizon Problem. Explain why regions of the CMB further apart than 2 were causally disconnected at the time of Recombination. Why does the uniformity of the CMB then pose a problem? This is the Horizon Problem. How does inflation solve the problem? If the Universe is decelerating, does stuff appear or disappear over our horizon? If on the other hand the Universe is accelerating, does stuff appear or disappear over our horizon?

  11. Isotropy Problem. The Microwave Background is isotropic to a few parts in 105. Why does this isotropy pose such a puzzle, given that galaxies exist at the present time? This is the Isotropy Problem. How might Dark Matter solve this problem?