Physics PHYS 102

General Astronomy


Problem Set #8 -- OPTIONAL -- DUE: Thursday, April 28th


After you finish this problem set, you should be familiar with:

Fundamental Forces

Evidence for Big Bang:




Cosmological redshift




Relative abundance




Microwave background




Olber’s Paradox


Problems with Big Bang:





Big Bang Cosmology

Homogeneity & Isotropy

Inflationary Big Bang model

Galaxy formation

Steady State Cosmology

Baryon asymmetry

Dark energy



Please answer the following questions using sentences and paragraphs.  When it is helpful, please use diagrams and equations.

  1. Suppose you suspected a certain object in the sky to be a quasar. What sort of observations might you perform to confirm your hypothesis?
  2. What is Hubble's law, and how is it used?  Does Hubble's law apply to stars, or just galaxies?  Explain.  About how far away is a galaxy that is moving at 20,000 km/sec? 

  3. List the four forces in nature, and describe an example of each one. Do you think it is possible that a fifth force might be discovered someday?
  4. Explain what is meant by a grand unified theory (GUT). Why are physicists so excited by the possibility of such a theory?
  5. Why do modern astronomers prefer the Big Bang model to Newton’s or the Steady-State cosmologies? Do you agree with the astronomers about the Big Bang?  Why or why not?
  6. Describe what is meant by positively curved, negatively curved, and flat space. What is meant by a closed or open universe?  How does the geometry of the universe affect the final state of the universe?
  7. Why do astronomers now think that the expansion of the universe is accelerating?  What are mechanisms are offered as possible explanations? What are the ramifications of this if it is true? 
  8. Your textbook indicates that "science cannot yet tell us what caused the big bang or what, if anything, existed before the big bang occurred."  Analyze this statement.  Are these scientific questions?


Here are some practice "figure it out rather than memorize" type questions.  They will not be graded as part of the homework (so don't turn them in), but they may be useful as you prepare for the test.  More questions like these can be found in the test practice folder at the library.


If the elliptical galaxy in Boötes, shown at the bottom of Fig. 16-29, Comins and Kaufmann, Discovering the Universe, 7th Ed., were to be at a distance of 1.6 billion ly, what would be the value of Hubble's constant H0? (Be careful with units.)



About 60 km/s per Mpc



About 25 km/s per Mpc



About 95 km/s per Mpc



About 80 km/s per Mpc



If Hubble's constant is 75 km/s/Mpc, then the age of the universe is 13 billion years. Suppose it were discovered that Hubble's constant is actually larger than 75 km/s/Mpc. What effect would this have on the calculated age of the universe?



It could increase or decrease the calculated age, depending on the recession velocity of the galaxy being investigated.



It would have no effect on the calculated age.



It would decrease the calculated age.



It would increase the calculated age.