Cosmology: The Origin and Evolution of the Universe

Note guide for Target 3: I can estimate the age of the universe from its expansion rate.

Key Concepts:

1. The Big Bang: The universe began as an infinitely dense cosmic singularity that begun its expansion in the event called the Big Bang, which can be described as the beginning of time.

2. The observable universe extends about 14 billion light-years in every direction from Earth. We cannot see objects beyond this distance because light from these objects has not had enough time to reach us.

3. During the first 10-43 seconds after the Big Bang, the universe was too dense to be described by the known laws of physics.

Questions:

1. How was the Big Bang different from an ordinary explosion?

2. Where did the universe occur?

3. Some people refer to the Hubble constant as the “Hubble variable.” In what sense is this justified?

4. What is meant by the observable universe? (Drawing a picture helps here)

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5. Explain why the radius of the observable universe is continually increasing.

6. Why can’t we see past the cosmological horizon?

7. Although the universe is 13.7 billion years old, the observable universe includes objects that are more than 13.7 billion light years away from Earth. Explain why.

8. Imagine an astronomer living in a galaxy a billion light years away. Is the observable universe for that astronomer the same as for an astronomer on Earth? Why or why not.

9. Estimate the age of the universe for a Hubble constant of

a. 50 km/s/Mpc

b. 75 km/s/Mpc

c. 100 km/s/Mpc

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10. Dr. Ammons believes that the Hubble constant is km/s/Mpc and Dr. Gregory believes it is km/s/Mpc. Which one believes the universe is younger. Provide evidence.

11. Find the value of the Hubble constant for a universe that is 6000 years old.

12. In general, how does the age of the universe depend on Hubble’s constant, and why?

13. Why does the value of Hubble’s constant alone not tell us the fate of the universe?

14. What is the Plank time?

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Notes:

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