2. What is meant in cosmology by "critical density"? A) The density of galaxies in rich clusters that prevents then escaping. B) The density needed to make a quark. C) The density that determines whether the Universe expands forever or re-collapses.. D) The density needed to create a gravitational lens. E) The density needed to create the Universe.
3. How does the observed density of luminous matter (stars and galaxies) in the Universe compare with the critical density? A) The density of luminous matter is far smaller than the critical density. B) Amazingly, the density of stars and galaxies exactly equals the critical density. C) The density of stars and galaxies is vastly bigger than the critical density.
4. Observations of the tiny ireegularities in the cosmic microwave background support the idea that the Universe A) will collapse in about 15 billion years. B) contains no dark matter. C) will expand forever. D) is made mostly of neutrinos. E) is made mostlyof antimatter.
5. Many astronomers think the Universe is flat. How do they reach this conclusion? A) They see no bending of light. B) They see huge numbers of gravitational lenses that flatten space. C) The can see that the cosmic background radiation is absolutely smooth with not even the tiniest trace of lumps. D) They can see an edge to space, proving it is npot curved. E) They think the Universe contains lots of dark matter and energy so that the density = the critical density.
6. Dividing the separation of two galaxies by their recession speed is a simple way to estimate A) the density of the Universe. B) if the Universe is flat. C) if the Universe contains dark matter. D) the age of the Universe. E) the strength of the CMB.
7. What is meant by the standard candle method? A) It's a way to weigh galaxies.. B) It's a way to measure the temperature of the CMB. C) It's a way to measure the temperature of the young Universe.. D) It's a way to find distances to nearby galaxies. E) It's how we know that active galaxies have black holes..
8. Suppose the Hubble constant turned out to be 130 km/sec/mpc and not 65 km/sec/mpc. How would that affect our estimate of the age of the Universe. A) The Universe would be about 30 billion yrs old. B) The Universe would be about 7 billion yrs old C) The Universe would be about 130 billion yrs old. D) It would have no effect on our estimates of the Universe's age. E) None of the above
9. What holds the local group together? A) The strong force. B) The electromagnetic force. C) ) The unified force. D) The cosmological constant. E) Gravity.
10. About how big across is the Local Group? A) A few million lyrs. B) A few million miles. C) A few dozen lyrs. D) About 100 trillion lyrs. E) 83,357 lyrs
11. This one has no exact answer. You should look at the sketch of "galaxies" in a "galaxy cluster" below and using what you know about the size of real galaxies, estimate the size of the cluster and the typical distant apart that the galaxies are. Check your answer against values in the text.
Your Answers Q1: Q2: Q3: Q4: Q5: Q6: Q7: Q8: Q9: Q10:
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