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closed universe critical density dark matter
flat universe open universe  

Review Questions

  1. What is the overall curvature of space in a closed or open or flat universe? How does the expansion rate compare to the amount of gravity deceleration in each of these cases?
  2. Why is the universe's expansion rate slowing down?
  3. Will it ever slow down completely? How can you find out?
  4. What type of universe has a critical density? What would happen to the expansion if the current density < critical density? How about the case for the current density > critical density?
  5. Would a universe starting out with a density > critical density ever expand enough so its density dropped below critical density? Explain why or why not!
  6. What is all the fuss about dark matter? If it is not putting out any light for us to see, how is it known to exist? What are some examples of observations indicating its presence?
  7. How can you use the cosmic microwave background (something from the far past) to determine the fate of the universe (something in the far future)?

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last updated: June 2, 2007

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Author of original content: Nick Strobel