<p> Cosmology: The Origin and Evolution of the Universe</p><p>Note guide for Target 3: I can estimate the age of the universe from its expansion rate.</p><p>Key Concepts:</p><p>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.</p><p>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.</p><p>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.</p><p>Questions:</p><p>1. How was the Big Bang different from an ordinary explosion?</p><p>2. Where did the universe occur?</p><p>3. Some people refer to the Hubble constant as the “Hubble variable.” In what sense is this justified?</p><p>4. What is meant by the observable universe? (Drawing a picture helps here)</p><p>Stars, Galaxies and Cosmology Page 1 Cosmology: The Origin and Evolution of the Universe</p><p>5. Explain why the radius of the observable universe is continually increasing.</p><p>6. Why can’t we see past the cosmological horizon?</p><p>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.</p><p>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.</p><p>9. Estimate the age of the universe for a Hubble constant of </p><p> a. 50 km/s/Mpc</p><p> b. 75 km/s/Mpc</p><p> c. 100 km/s/Mpc</p><p>Stars, Galaxies and Cosmology Page 2 Cosmology: The Origin and Evolution of the Universe</p><p>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.</p><p>11. Find the value of the Hubble constant for a universe that is 6000 years old.</p><p>12. In general, how does the age of the universe depend on Hubble’s constant, and why?</p><p>13. Why does the value of Hubble’s constant alone not tell us the fate of the universe?</p><p>14. What is the Plank time?</p><p>Stars, Galaxies and Cosmology Page 3 Cosmology: The Origin and Evolution of the Universe</p><p>Notes:</p><p>Stars, Galaxies and Cosmology Page 4</p>