Choose the best answer for the following question.
When the universe was 380,000 years old, its thermal radiation spectrum consisted mostly of
(a) radio and microwave photons.
(b) visible and infrared photons.
(c) X-ray and ultraviolet photons.

Answer the following questions based on the information provided.
How much cooler is the universe now (at an age of $4\times10^{17}$ s) than it was at an age of 1 second?
a. Its current temperature is one hundred-millionth ($10^{-8}$) the temperature at an age of 1 second.
b. Its current temperature is one hundred-thousandth ($10^{-5}$) the temperature at an age of 1 second.
c. Its current temperature is one-hundredth ($10^{-2}$) the temperature at an age of 1 second.
d. Its current temperature is one ten-billionth ($10^{-10}$) the temperature at an age of 1 second.

What are the four forces that operate in the universe today? Why do we think there were fewer forces operating in the early universe?

Choose the best answer for the following question.
Which of the following does not provide strong evidence for the Big Bang theory?
(a) observations of the cosmic microwave background
(b) observations of the amount of hydrogen in the universe
(c) observations of the ratio of helium to hydrogen in the universe

Choose the best answer for the following question.
When a proton and an antiproton collide, they
(a) repel each other.
(b) fuse together.
(c) convert into two photons.

Choose the best answer for the following question.
The charge of an antiproton is
(a) positive.
(b) negative.
(c) neutral.

Choose the best answer for the following question.
Which of the following quasars would you expect to have the largest number of hydrogen absorption lines in its spectrum?
(a) a quasar with a lookback time of 1 billion years
(b) a quasar with a lookback time of 8 billion years
(c) a quasar with a lookback time of 13 billion years

Choose the best answer for the following question.
The current temperature of the universe as a whole is
(a) absolute zero.
(b) a few K.
(c) a few thousand K

a. A clever student, after learning about the theory of relativity, decides to apply his knowledge in order to prolong his life. He decides to spend the rest of his life in a car, traveling around the freeways at 55 miles per hour (89 km/hr). Suppose he drives for a period of time during which 70 years pass in his house. How much time will pass in the car? (Hint: If you are unable to find a difference, be sure to explain why.)
b. An even more clever student decides to prolong her life by cruising around the local solar neighborhood at a speed of 0.95c (95% of the speed of light). How much time will pass on her spacecraft during a period in which 70 years pass on Earth? Will she feel as if her life span has been extended? Explain. c. Suppose you stay home on Earth while your twin sister takes a trip to a distant star and back in a spaceship that travels at 99% of the speed of light. If both of you are 25 years old when she leaves and you are 45 years old when she returns, how old is your sister when she gets back?

Latitude Distance. Earth’s radius is approximately $6370$ km.
a. What is Earth’s circumference?
b. What distance is represented by each degree of latitude?
c. What distance is represented by each arcminute of latitude?
d. Can you give similar answers for the distances represented by a degree or arcminute of longitude? Why or why not?

Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). Explain clearly.
Patterns in the cosmic microwave background tell us about conditions in the early universe that ultimately led to galaxy formation.

Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). Explain clearly.
The main reason the night sky is dark is that stars are so far away.

Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). Explain clearly.
In the distant past, the cosmic microwave background consisted primarily of infrared light.

Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). Explain clearly.
Inflation is a nice idea, but there are no known ways to test whether it really happened.