Explorations: An Introduction to Astronomy (Arny), 7th Edition

Chapter 18: Cosmology

Questions for Review

1
Why do astronomers think that the Universe is expanding?
2
What is meant by the age of the Universe? How old is the Universe? How is its age found?
3
How can there be no center to the Universe?
4
What is Olbers' paradox?
5
What is meant by a cosmic horizon?
6
Is our cosmic horizon the same as that of beings in another galaxy? Why?
7
What does "light travel time distance" mean?
8
What happened at the recombination era? Why is this important today?
9
What is the cosmic microwave background? What is its origin?
10
Why do astronomers think that the early Universe was hot and dense?
11
According to the Big Bang theory, what were the major eras in the history of the Universe? What was the Universe like in each of them? Approximately how long did each last?
12
How was helium formed from hydrogen in the early Universe?
13
Why is Einstein's equation for the equivalence of mass and energy important when thinking about the early Universe?
14
What do astronomers mean when they say that the Universe is flat? What are the other possibilities?
15
What evidence do astronomers have that the Universe is flat?
16
What is meant by inflation in cosmology?
17
What problems of the Big Bang theory are resolved by inflationary models?
18
What role does the cosmological constant play in cosmology? Is this the same role Einstein originally created it for? What evidence makes astronomers think it may exist?
19
What determines whether the Universe will expand forever or recollapse? Explain what the critical density is.
20
What is dark energy? What does its presence imply for the future of the Universe?
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