Exam Prep The Evolution of the Universe Ch.16

Chapter 16: The Evolution of the Universe

LEARNING OBJECTIVES

16.1 Hubble’s Law Implies a Hot, Dense Beginning

16.1a Explain why Hubble expansion observed today implies the universe was smaller and hotter in the past.

16.1b Explain how expanding space leads to the redshift of light from distant objects.

16.2 The Cosmic Microwave Background Confirms the Big Bang

16.2a Explain why we expect the universe to be filled with a cosmic microwave background.

16.2b Describe the observed characteristics of the cosmic microwave background.

16.2c Characterize the conditions in the early universe based on the currently observed cosmic microwave background.

16.3 The Expansion of the Universe Is Speeding Up

16.3a Explain why the mass in the universe determines its fate.

16.3b Explain the effects of dark energy.

16.3c Characterize how the amounts of matter and dark energy in the universe determine its evolution and fate.

16.4 The Earliest Moments of the Universe Connect the Very Largest Size Scales to the Very Smallest

16.4a List the four fundamental forces of nature.

16.4b Describe the relationship between temperature of the universe and unification of forces.

16.4c Explain how the events that occurred in the early universe are related to the forces that operate in the universe today.

16.4d Assess whether string theory is a scientific theory.

16.4e Describe the processes of pair production and annihilation.

16.5 Inflation Solves Several Problems in Cosmology

16.5a Explain how inflation solves the horizon and flatness problems.

16.6 Other Universes?

16.6a Assess whether multiverses are a scientific theory.

Working It Out 16.1

Working It Out 16.1a Use Hubble’s law to estimate the age of the universe.

Chapter 16: The Evolution of the Universe

MULTIPLE CHOICE

1. Why does the expansion of space cause redshifts of distant galaxies?

a. The amount of space in between the galaxies is increasing.

b. All galaxies are moving away from us because we are at the center of the universe.

c. All galaxies are moving toward us because we are at the center of the universe.

d. Galaxies do not show redshifts.

2. Which of the following is a prediction of the standard Big Bang theory that has been successfully verified by observations?

a. The universe is static.

b. The faintest galaxies look redder because their stars are younger.

c. Helium, lithium, and beryllium were made as the universe cooled soon after the initial Big Bang.

d. The early universe was cool and dense.

3. Was the Big Bang an explosion that flung debris throughout space?

a. Yes, the debris made the first stars.

b. Yes, the debris made protons, neutrons, and electrons.

c. No, the Big Bang formed space and time in a rapid expansion.

d. No, the debris was already present.

4. Where in the universe did the Big Bang take place?

a. near the Milky Way Galaxy

b. near the Virgo Cluster

c. near some unknown location on the other side of the universe

d. everywhere in the universe

5. The inverse of the value of H₀ is a

a. time. c. density.

b. mass. d. size.

6. Given the value of H₀ as 700 kilometers per second per megaparsec (km/s/Mpc) and that a megaparsec is 3.086 10¹⁹ km, what is the Hubble time in years?

a. 70 years (yr) c. 1.4 10^-2 yr

b. 1.4 10¹⁰ yr d. 2.1602 10²¹ yr

7. What assumption about the universe is made using the Hubble time to estimate the age of the universe?

a. static universe c. slowing expansion

b. accelerating expansion d. constant expansion

8. Given a value of H₀ as 50 km/s/Mpc, what velocity would you expect to see for a galaxy that is 30 Mpc away from the Milky Way?

a. 2,100 km/s c. 80,000 km/s

b. 1,500 km/s d. 1.4 10¹⁰ km/s

9. Examine the following figure. What can you say about the ratio of distance to velocity for each galaxy as you look farther away? The ratio

a. goes up. c. stays the same.

b. goes down. d. goes up and then down.

10. How would the linear fit and the value of H₀ change in the following plot if the universe were expanding faster than it is today? The line would be

a. steeper and H₀ would be smaller. c. shallower and H₀ would be smaller.

b. steeper and H₀ would be bigger. d. shallower and H₀ would be bigger.

11. How would the linear fit and the value of H₀ change in the following plot if the universe were expanding slower than it is today? The line would be

a. steeper and H₀ would be smaller. c. shallower and H₀ would be smaller.

b. steeper and H₀ would be bigger. d. shallower and H₀ would be bigger.

12. In the early 1960s, physicists named Penzias and Wilson detected a persistent noise at a wavelength of 1 millimeter (mm) in their radio telescope. The persistent noise that Penzias and Wilson detected came from all directions in the sky as a result of

a. synchrotron emission from the Crab Nebula.

b. emission from newly formed stars in the Orion Nebula.

c. cell phone usage.

d. photons leftover from the Big Bang.

13. The existence of the cosmic microwave background radiation tells us that the early universe was

a. much hotter than it is today.

b. much colder than it is today.

c. composed entirely of radiation at early times.

d. composed entirely of stars at early times.

14. After the Big Bang, as the universe cooled and protons and electrons combined so that the universe became neutral, what important consequence happened?

a. Photons began to travel freely through the universe.

b. Neutrinos ceased to interact with normal matter.

c. Dark matter ceased to interact with normal matter.

d. Protons and neutrons combined to form nuclei such as deuterium and helium.

15. The current temperature of the cosmic microwave background radiation of 2.73 kelvin (K) means that the peak of its spectrum occurs at a wavelength of

a. gamma rays. c. microwaves.

b. infrared. d. ultraviolet.

16. What prevents us from looking all the way back to the Big Bang itself?

a. Photons are not produced until the stars form.

b. At such high redshifts, photons are gravitationally lensed by the dark matter in the universe.

c. At such high redshifts, most of the photons are blocked by large amounts of cold gas and dust.

d. The very early universe was so hot that matter was ionized and photons were blocked by free electrons in the universe.

17. Examine the following plot of the brightness versus wavelength data of the cosmic microwave background. What temperature gives a blackbody curve that fits these data?

a. 1 K c. 1000 K

b. 2.73 K d. 3000 K

18. Examine the following image of the cosmic microwave background (CMB) temperature map from early data collected by the Cosmic Background Explorer (COBE) satellite. Why are there differing temperatures for the universe?

a. The early universe had uneven temperatures.

b. The COBE data were corrupt.

c. The Milky Way blocks some of the signal.

d. The Sun’s motion relative to the CMB causes the observed asymmetry.

19. Examine the following image of the corrected CMB temperature map obtained by the COBE satellite. What causes the tiny (0.001%) brightness variations scattered all over the universe?

a. The early universe had drastically uneven temperatures.

b. The COBE data were affected by material in the Milky Way.

c. They are the result of gravitational redshifts caused by concentrations of mass in the early universe.

d. Earth’s motion relative to the CMB causes the observed asymmetry.

20. Which satellite produced this image, which is the highest resolution map of the CMB?

a. Wilkinson Microwave Anisotropy Probe (WMAP)

b. COBE

c. Planck

d. Echo 1

21. What surprising result came of the highest resolution map of the CMB?

a. The Big Bang theory was falsified.

b. A cool spot was confirmed.

c. Previous missions were largely found erroneous.

d. The early universe’s temperature was absolute zero.

22. Why does the overall mass and energy density of the universe decide its ultimate fate? The greater the density of the universe,

a. the more black holes will form, which will devour surrounding material more quickly.

b. the more gravitationally bound the universe will be.

c. the more massive stars it will contain, and the faster it will evolve.

d. the more stars it will form over time, and the longer the universe will last.

23. If today and there were no dark energy, the universe would

a. expand forever.

b. slow its expansion but never reverse it.

c. stop expanding and eventually collapse.

d. oscillate between expansion and collapse.

24. If the fate of the universe were determined SOLELY by what we currently know to be the total mass of the universe in luminous and dark matter (excluding dark energy), astronomers would predict that we live in a universe that will

a. expand forever.

b. slow its expansion but never reverse it.

c. stop expanding and eventually collapse.

d. oscillate between expansion and collapse.

25. In the 1990s, astronomers found that distant Type Ia supernovae were __________ than they expected, leading them to conclude that __________.

a. brighter; the universe’s expansion rate was decreasing with time

b. brighter; the universe was finite in size

c. fainter; the universe’s expansion rate has been increasing with time

d. fainter; the universe was infinite in size

26. How does the addition of a nonzero cosmological constant affect the expansion of the universe?

a. It is possible for the mass density of the universe to be below the critical density and still collapse.

b. It is possible for the density of the universe to be above the critical density and still expand forever.

c. It is impossible to have a collapsing universe, regardless of its density.

d. It is impossible to have an expanding universe, regardless of its density.

27. Observations of Type Ia supernovae in distant galaxies have shown that

a. the star formation rate in galaxies decreases with increasing redshift.

b. the expansion rate of the universe is increasing.

c. the cosmological constant is zero.

d. dark energy is negligible at the present time.

28. Because we live in a universe with an accelerating expansion rate, the actual age of the universe is __________ the Hubble time.

a. larger than c. the same as

b. smaller than d. independent of

29. Why was the discovery of dark energy unexpected?

a. The gravity provided by the mass contained within the universe was predicted to slow the expansion.

b. The acceleration of the universe was predicted to increase.

c. Astronomers had not anticipated being able to observe supernovae at such large distances.

d. The universe was expected to lose, not gain, energy.

30. The critical density of the universe is approximately equal to

a. 1 proton per cubic meter (m³). c. 1 Earth mass/m³.

b. 1 kg/m³. d. 1 solar mass/m³.

31. Current observations suggest that the densities of luminous matter (), all matter (), and dark energy () are

a. .

b. .

c. .

d. .

32. If today and dark energy is a cosmological constant, the universe will

a. expand forever. c. stop expanding and eventually collapse.

b. slow its expansion but never reverse it. d. oscillate between expansion and collapse.

33. A grand unified theory unites which forces?

a. only electromagnetism, weak nuclear, and strong nuclear

b. only gravity and strong nuclear

c. only electromagnetism, gravity, and weak nuclear

d. all four known forces

34. Soon after the Big Bang, we think the four fundamental forces of nature were united into one superforce, and __________ was the first to split off from the others.

a. the strong force c. gravity

b. electromagnetism d. nucleosynthesis

35. By the time the universe was a few minutes old, the majority of the normal matter in the universe was hydrogen, and the remainder was mostly __________.

a. helium c. neutrinos

b. neutrons d. protons

36. List the four fundamental forces of nature.

a. electromagnetic, gravity, strong nuclear, and weak nuclear

b. electroweak, gravity, magnetic, and nuclear

c. gravity, magnetism, strong nuclear, and weak nuclear

d. electrostrong, gravity, magnetic, and nuclear

37. Which of the following was created in the early universe as a result of the Big Bang?

a. helium c. deuterium

b. lithium d. All are valid choices.

38. How would astronomers describe the antiparticle of an electron?

a. same mass but opposite charge c. opposite charge and higher mass

b. same charge but opposite spin d. opposite spin and higher mass

39. What would the universe be like if there were complete symmetry between matter and antimatter?

a. It would look similar to our universe, but half of it would be composed of antimatter.

b. We would observe two universes, one an antimatter reflection of the other.

c. There would be no universe because all of the matter and antimatter would have been annihilated.

d. There would be a universe, but it would be completely composed of photons.

40. Grand unified theories are very attractive because they can explain why

a. the universe consists mostly of matter.

b. the Big Bang never made any antimatter.

c. we have five fundamental forces in the universe today.

d. the cosmic microwave background radiation is very smooth.

41. Even with infinitely powerful telescopes, we can look back in time only until

a. when galaxies were first formed. c. when gravity was quantum mechanical.

b. when hydrogen and helium were formed. d. the time of recombination.

42. The standard model of particle physics is incomplete because it leaves which question(s) unanswered?

a. Why do neutrinos have mass?

b. Why is the strong nuclear force much stronger than the weak nuclear force?

c. How is gravity related to the other three fundamental forces?

d. all of the above

43. About what was the temperature of the universe when photons were no longer colliding with enough energy to create electron and positron pairs?

a. 1000 K c. 1 million K

b. 100,000 K d. 1 billion K

44. In some particle physics theories, the universe must have more than three spatial dimensions, but we experience only three. Why would we not see the other spatial dimensions?

a. The other six spatial dimensions are tightly wrapped around each other and have not expanded.

b. The other nine spatial dimensions are too small to be noticeable.

c. The other seven spatial dimensions undergo inflation and flatten themselves out.

d. The other nine spatial dimensions wrap around each other and form the temporal dimension.

45. At what stage in the universe’s history do we think the asymmetry between matter and antimatter was created?

a. at the very moment the Big Bang occurred

b. about the time gravity separated out of the theory of everything

c. about the time the strong force separated out of the grand unified theory

d. about the time the weak force and electromagnetism separated

46. The flatness problem arises because only a universe with __________ can have that value forever.

a. c.

b. d.

47. What can simultaneously solve both the flatness and horizon problems in cosmology?

a. grand unified theories (GUTs) c. inflation

b. quantum mechanics d. dark energy

48. Inflation happened when

a. the universe was seconds old.

b. the universe expanded by a factor of approximately 10³⁰.

c. the average energy of the vacuum of spacetime changed.

d. all of the above

49. If multiverses exist, which of the following is correct?

a. Each universe is identical to every other.

b. Multiverses are not allowed by the laws of physics as we understand them.

c. The universes can never communicate with each other.

d. You have lived your exact same life in every universe.

50. Whether or not parallel universes exist is hard to determine because

a. our universe is so big.

b. the parallel universes cannot communicate with each other.

c. the other universes do not emit any light.

d. parallel universes destroy each other if they come into contact.

1. Draw in the following graph a line that would fit data if the universe were expanding at a faster rate.

2. Draw in the following graph a line that would fit data if the universe were expanding at a slower rate.

3. Assuming the Hubble constant is equal to 70 km/s/Mpc, estimate the age of the universe (or Hubble time). Note that 1 Mpc 3.1 10¹⁹ km, and 1 year 3.17 10⁷ seconds.

4. Assuming the Hubble constant is equal to 50 km/s/Mpc, estimate the age of the universe (or Hubble time). Note that 1 Mpc 3.1 10¹⁹ km, and 1 year 3.17 10⁷ seconds.

5. What important event in the universe’s history marked the creation of the cosmic microwave background radiation?

6. Name two predictions of the standard Big Bang theory that have been verified by observations.

7. The COBE and WMAP satellites detected fluctuations in the cosmic microwave background radiation. On average, how big were these fluctuations, and what do they tell us about the very early universe?

8. The cosmic microwave background radiation has a temperature of approximately 2.7 K and a Planck blackbody spectrum. Calculate the wavelength where the cosmic microwave background radiation spectrum peaks.

9. What will happen to the expansion of the universe in the future if (a) , (b) , and (c) ?

10. If dark energy is currently causing the expansion rate of the universe to increase with time, does this mean that you should worry that the Sun, Earth, and your body itself are expanding? Why or why not?

11. Why does the sum of and determine the shape of our universe?

12. Why does the critical mass density of the universe depend on the value of the Hubble constant, H₀?

13. What is the difference between a grand unified theory and a theory of everything (TOE)?

14. Why is the universe made up of matter as opposed to antimatter?

15. Describe the four fundamental forces of nature by listing their names and describing what effect each force has on objects in the universe.

16. Explain why astronomers cannot accurately model the exact history of the universe in the first few fractions of a second after the Big Bang.

17. Explain why Einstein invented the cosmological constant.

18. Explain the physical significance that the cosmological constant has today.

19. What is the “flatness problem” in cosmology?

20. What can solve the flatness and horizon problem in cosmology, and why?