Question 1

According to the current understanding of cosmology, what is the origin of the foamy structure of the universe, with clusters of galaxies distributed on the perimeters of voids?

Accepted Answer

A)  The early epoch of star formation caused the clusters of galaxies to repel one another, and the present distribution was the result. 
B)  The matter in the universe is now believed to be very smoothly distributed, just as it was after the Big Bang. What astronomers see as voids is really dark matter. 
C)  Quantum fluctuations in the early universe were greatly exaggerated during the epoch of inflation to become the uneven distribution astronomers now observe. 
D)  The universe was formed "clumpy" in the Big Bang, and the clumpiness persists to the present day. 
A)  The early epoch of star formation caused the clusters of galaxies to repel one another, and the present distribution was the result. 
B)  The matter in the universe is now believed to be very smoothly distributed, just as it was after the Big Bang. What astronomers see as voids is really dark matter. 
C)  Quantum fluctuations in the early universe were greatly exaggerated during the epoch of inflation to become the uneven distribution astronomers now observe. 
D)  The universe was formed "clumpy" in the Big Bang, and the clumpiness persists to the present day.

Question 2

What is the ratio of cosmic microwave background photons to hydrogen atoms, on average, in the universe?

Accepted Answer

A)  about 1 billion to 1 
B)  about 1 million to 1 
C)  about 1 to 100-very few microwave photons 
D)  about 1 to 1-equal numbers of photons and hydrogen atoms 
A)  about 1 billion to 1 
B)  about 1 million to 1 
C)  about 1 to 100-very few microwave photons 
D)  about 1 to 1-equal numbers of photons and hydrogen atoms

Question 3

The farther away a galaxy is, the more its light is redshifted, as observed from Earth. This relationship between redshift and distance is caused by

Accepted Answer

A)  the Doppler shift of light leaving a moving object. More distant galaxies are moving faster through space, so their light is more strongly Doppler-shifted (redshifted). 
B)  energy losses. The universe does not really expand; photons simply lose energy (wavelength lengthens) as they travel. Photons from more distant galaxies have traveled farther and so are more redshifted. 
C)  the expansion of space itself, which stretches the wavelength of the photon. The longer the time the photon has traveled, the more space has expanded and therefore the more the photon has been redshifted. 
D)  the gravitational redshift. Photons leaving a more distant galaxy have traveled farther through the galaxy's gravitational field, so they have lost more energy and are more redshifted. 
A)  the Doppler shift of light leaving a moving object. More distant galaxies are moving faster through space, so their light is more strongly Doppler-shifted (redshifted). 
B)  energy losses. The universe does not really expand; photons simply lose energy (wavelength lengthens) as they travel. Photons from more distant galaxies have traveled farther and so are more redshifted. 
C)  the expansion of space itself, which stretches the wavelength of the photon. The longer the time the photon has traveled, the more space has expanded and therefore the more the photon has been redshifted. 
D)  the gravitational redshift. Photons leaving a more distant galaxy have traveled farther through the galaxy's gravitational field, so they have lost more energy and are more redshifted.

Question 4

If astronomers could have turned a receiver toward the heavens in hopes of observing the cosmic microwave radiation 4.5 billion years ago, at the time the solar nebula was forming, what would they have found?

Accepted Answer

A)  They would have seen nothing since the cosmic microwave background had not yet been created. 
B)  They would have seen the same blackbody curve seen now, with a peak intensity at a wavelength of about 1 mm. 
C)  They would have seen a blackbody curve of the same shape seen now but with a peak intensity at a wavelength shorter than 1 mm. 
D)  They would have seen a blackbody curve of the same shape seen now but with a peak intensity at a wavelength longer than 1 mm. 
A)  They would have seen nothing since the cosmic microwave background had not yet been created. 
B)  They would have seen the same blackbody curve seen now, with a peak intensity at a wavelength of about 1 mm. 
C)  They would have seen a blackbody curve of the same shape seen now but with a peak intensity at a wavelength shorter than 1 mm. 
D)  They would have seen a blackbody curve of the same shape seen now but with a peak intensity at a wavelength longer than 1 mm.

Question 5

For any object moving uniformly, velocity = distance/time. So in the Hubble relationship for the expansion of the universe, v = H0r, what is the significance of the constant 1/H0?

Accepted Answer

A)  This quantity represents the average spacing between objects in the universe at the present time. 
B)  This quantity represents the time since the expansion began, or the age of the universe. 
C)  This quantity is merely a constant of proportionality to allow for the different units in v and r. 
D)  This quantity is the inverse of the velocity that the object would have at a standard distance of 10 parsecs. 
A)  This quantity represents the average spacing between objects in the universe at the present time. 
B)  This quantity represents the time since the expansion began, or the age of the universe. 
C)  This quantity is merely a constant of proportionality to allow for the different units in v and r. 
D)  This quantity is the inverse of the velocity that the object would have at a standard distance of 10 parsecs.

Question 6

In order to estimate the age of the universe as 1/H0 , astronomers must make a number of assumptions. Which of these is NOT one of the necessary assumptions?

Accepted Answer

A)  The universe's expansion rate is the same in all directions. 
B)  The Milky Way Galaxy is the center of the universal expansion. 
C)  The value of H0 is indeed constant. 
D)  The speed of the expansion has been constant through time. 
A)  The universe's expansion rate is the same in all directions. 
B)  The Milky Way Galaxy is the center of the universal expansion. 
C)  The value of H0 is indeed constant. 
D)  The speed of the expansion has been constant through time.

Question 7

Which one of these is NOT believed to be a characteristic of Population III stars?

Accepted Answer

A)  They were composed of almost pure hydrogen. 
B)  They formed from small clouds of gas so are less massive than the Sun. 
C)  They were formed soon after the Big Bang. 
D)  Most have long since disappeared. 
A)  They were composed of almost pure hydrogen. 
B)  They formed from small clouds of gas so are less massive than the Sun. 
C)  They were formed soon after the Big Bang. 
D)  Most have long since disappeared.

Question 8

The weak force

Accepted Answer

A)  acted only during the Big Bang and has no known role in the universe at the present time. 
B)  holds the quarks together inside a proton or neutron. 
C)  attracts the electrons to the nucleus, holding the atom together. 
D)  acts during certain kinds of radioactive decay. 
A)  acted only during the Big Bang and has no known role in the universe at the present time. 
B)  holds the quarks together inside a proton or neutron. 
C)  attracts the electrons to the nucleus, holding the atom together. 
D)  acts during certain kinds of radioactive decay.

Question 9

Consider a universe without dark energy (i.e., all the energy in the universe produces an attractive gravitational force). What will happen if the universe is closed?

Accepted Answer

A)  The universe will expand past its maximum size, then fragment into miniuniverses. 
B)  The universe will eventually fall back in on itself, heading toward a "Big Crunch." 
C)  The universe will expand forever. 
D)  The universe will reach a maximum size and remain there, like a balloon being blown up. 
A)  The universe will expand past its maximum size, then fragment into miniuniverses. 
B)  The universe will eventually fall back in on itself, heading toward a "Big Crunch." 
C)  The universe will expand forever. 
D)  The universe will reach a maximum size and remain there, like a balloon being blown up.

Question 10

Consider four different regimes of space in which distances between objects might be changing as a result of the general expansion of the universe: (1) distances between different parts of Earth; (2) distance between planets in the solar system; (3) distances between stars in the Milky Way; (4) distances between clusters of galaxies. In which of these regimes are the distances changing because of the universe's expansion?

Accepted Answer

A)  4, 3, 2, 1 
B)  4 
C)  4, 3, 2 
D)  4, 3 
A)  4, 3, 2, 1 
B)  4 
C)  4, 3, 2 
D)  4, 3

Question 11

Who discovered the cosmic microwave background radiation, the radiation left over from the Big Bang?

Accepted Answer

A)  Ralph Alpher and George Gamow 
B)  Arno Penzias and Robert Wilson 
C)  Anthony Hewish and Jocelyn Bell 
D)  Robert Dicke and P. J. E. Peebles 
A)  Ralph Alpher and George Gamow 
B)  Arno Penzias and Robert Wilson 
C)  Anthony Hewish and Jocelyn Bell 
D)  Robert Dicke and P. J. E. Peebles

Question 12

When did Einstein originally introduce his theory of general relativity, including the cosmological constant?

Accepted Answer

A)  in 1896, before the modern stellar spectral classification scheme was devised 
B)  in 1915, before the question of the nature of the Milky Way Galaxy had been resolved 
C)  in 1930, after Hubble had discovered evidence for the expanding universe 
D)  in 1968, after the discovery of the cosmic microwave background gave evidence of the Big Bang 
A)  in 1896, before the modern stellar spectral classification scheme was devised 
B)  in 1915, before the question of the nature of the Milky Way Galaxy had been resolved 
C)  in 1930, after Hubble had discovered evidence for the expanding universe 
D)  in 1968, after the discovery of the cosmic microwave background gave evidence of the Big Bang

Question 13

During what time interval was helium created in the Big Bang?

Accepted Answer

A)  during the first 10-43 s 
B)  during the first 10-6 s 
C)  during the first 500,000 years 
D)  during the first 3 minutes 
A)  during the first 10-43 s 
B)  during the first 10-6 s 
C)  during the first 500,000 years 
D)  during the first 3 minutes

Question 14

During the first millionth of a second in the history of the universe, a hydrogen nucleus could NOT exist. Why not?

Accepted Answer

A)  During this time quarks existed in isolation and so protons did not exist. 
B)  The electromagnetic force did not exist during this era. 
C)  Cosmic inflation had pushed protons and electrons too far apart to interact with each other. 
D)  Protons and antiprotons were continually annihilating each other, and there were no protons to form hydrogen atoms. 
A)  During this time quarks existed in isolation and so protons did not exist. 
B)  The electromagnetic force did not exist during this era. 
C)  Cosmic inflation had pushed protons and electrons too far apart to interact with each other. 
D)  Protons and antiprotons were continually annihilating each other, and there were no protons to form hydrogen atoms.

Question 15

When the universe was about 30,000 years old, the radiation density had decreased to the point where it was equal to the matter density. Yet it was only many years later that atoms formed. What happened to make possible the formation of atoms?

Accepted Answer

A)  The average photon energy decreased until it could no longer ionize hydrogen. 
B)  Radiation pressure decreased until it was equal to the inward pressure due to gravity. 
C)  The temperature reached the point where the reaction 4 1H $\rightarrow$ 4He could proceed. 
D)  Neutrons decayed to produce protons and electrons, the building blocks of atoms. 
A)  The average photon energy decreased until it could no longer ionize hydrogen. 
B)  Radiation pressure decreased until it was equal to the inward pressure due to gravity. 
C)  The temperature reached the point where the reaction 4 1H $\rightarrow$ 4He could proceed. 
D)  Neutrons decayed to produce protons and electrons, the building blocks of atoms.

Question 16

What is the "particle horizon"?

Accepted Answer

A)  The particle horizon is the distance beyond which astronomers cannot see because light cannot have traveled any farther in the finite age of the universe. 
B)  The particle horizon is the distance beyond which astronomers cannot see because no stars or galaxies had yet formed at those distances (because astronomers see back in time as they look out into space). 
C)  The particle horizon is the distance beyond which signals from Earth radio and television signals cannot have traveled through the universe. 
D)  The particle horizon is the distance beyond which astronomers cannot see because of absorbing matter in the universe. 
A)  The particle horizon is the distance beyond which astronomers cannot see because light cannot have traveled any farther in the finite age of the universe. 
B)  The particle horizon is the distance beyond which astronomers cannot see because no stars or galaxies had yet formed at those distances (because astronomers see back in time as they look out into space). 
C)  The particle horizon is the distance beyond which signals from Earth radio and television signals cannot have traveled through the universe. 
D)  The particle horizon is the distance beyond which astronomers cannot see because of absorbing matter in the universe.

Question 17

When astronomers view a distant quasar with highly redshifted emission lines in its spectrum, this wavelength shift is a

Accepted Answer

A)  Doppler shift. 
B)  gravitational redshift. 
C)  cosmological redshift. 
D)  Doppler shift or a gravitational redshift or a cosmological redshift-they are one and the same thing. 
A)  Doppler shift. 
B)  gravitational redshift. 
C)  cosmological redshift. 
D)  Doppler shift or a gravitational redshift or a cosmological redshift-they are one and the same thing.

Question 18

The Big Bang theory is the most widely accepted model of the early universe today. Which of these is NOT one of the reasons for this?

Accepted Answer

A)  The observed expansion of the universe is consistent with the Big Bang theory. 
B)  No alternate theories have been proposed. 
C)  The observed cosmic microwave background is consistent with the Big Bang theory. 
D)  The observed cosmic neutrino background is consistent with the Big Bang theory. 
A)  The observed expansion of the universe is consistent with the Big Bang theory. 
B)  No alternate theories have been proposed. 
C)  The observed cosmic microwave background is consistent with the Big Bang theory. 
D)  The observed cosmic neutrino background is consistent with the Big Bang theory.

Question 19

Suppose that the expansion rate were slower in the past. Taking this fact into account when estimating the age of the universe from the presently accepted value of the Hubble constant, H0 = 73.5 km/s/Mpc, yields

Accepted Answer

A)  13.4 billion years, as before. 
B)  a value less than 13.4 billion years. 
C)  a value greater than 13.4 billion years. 
D)  a value different from 13.4 billion years, but additional information is needed to determine whether it is larger or smaller. 
A)  13.4 billion years, as before. 
B)  a value less than 13.4 billion years. 
C)  a value greater than 13.4 billion years. 
D)  a value different from 13.4 billion years, but additional information is needed to determine whether it is larger or smaller.

Question 20

The Milky Way Galaxy is moving at about 600 km/s relative to the cosmic microwave background radiation. Why?

Accepted Answer

A)  The Milky Way is being gravitationally attracted by several nearby superclusters of galaxies. 
B)  This speed is the orbital speed of the Local Group of galaxies around the Virgo cluster. 
C)  There is no particular reason. All galaxies have "small" random speeds in addition to the universal expansion, and 600 km/s is the speed of the Milky Way. 
D)  This speed is the orbital speed of the Milky Way Galaxy around the Andromeda Galaxy. 
A)  The Milky Way is being gravitationally attracted by several nearby superclusters of galaxies. 
B)  This speed is the orbital speed of the Local Group of galaxies around the Virgo cluster. 
C)  There is no particular reason. All galaxies have "small" random speeds in addition to the universal expansion, and 600 km/s is the speed of the Milky Way. 
D)  This speed is the orbital speed of the Milky Way Galaxy around the Andromeda Galaxy.

According to the current understanding of cosmology, what is the origin of the foamy structure of the universe, with clusters of galaxies distributed on the perimeters of voids?

What is the ratio of cosmic microwave background photons to hydrogen atoms, on average, in the universe?

The farther away a galaxy is, the more its light is redshifted, as observed from Earth. This relationship between redshift and distance is caused by

If astronomers could have turned a receiver toward the heavens in hopes of observing the cosmic microwave radiation 4.5 billion years ago, at the time the solar nebula was forming, what would they have found?

For any object moving uniformly, velocity = distance/time. So in the Hubble relationship for the expansion of the universe, v = H₀r, what is the significance of the constant 1/H₀?

In order to estimate the age of the universe as 1/H₀ , astronomers must make a number of assumptions. Which of these is NOT one of the necessary assumptions?

Which one of these is NOT believed to be a characteristic of Population III stars?

The weak force

Consider a universe without dark energy (i.e., all the energy in the universe produces an attractive gravitational force). What will happen if the universe is closed?

Who discovered the cosmic microwave background radiation, the radiation left over from the Big Bang?

When did Einstein originally introduce his theory of general relativity, including the cosmological constant?

During what time interval was helium created in the Big Bang?

During the first millionth of a second in the history of the universe, a hydrogen nucleus could NOT exist. Why not?

When the universe was about 30,000 years old, the radiation density had decreased to the point where it was equal to the matter density. Yet it was only many years later that atoms formed. What happened to make possible the formation of atoms?

What is the "particle horizon"?

When astronomers view a distant quasar with highly redshifted emission lines in its spectrum, this wavelength shift is a

The Big Bang theory is the most widely accepted model of the early universe today. Which of these is NOT one of the reasons for this?

Suppose that the expansion rate were slower in the past. Taking this fact into account when estimating the age of the universe from the presently accepted value of the Hubble constant, H₀ = 73.5 km/s/Mpc, yields

The Milky Way Galaxy is moving at about 600 km/s relative to the cosmic microwave background radiation. Why?

Discovering the Night Sky

Gravitation and the Motion of the Planets

Light and Telescopes

Atomic Physics and Spectra

Exoplanets and the Formation of Planetary Systems

Formation of the Solar System

Earth and the Moon

The Other Terrestrial Planets

The Outer Planets

Vagabonds of the Solar System

The Sun: Our Extraordinary Star

Characterizing Stars

The Lives of Stars From Birth Through Middle Age

The Death of Stars

Black Holes: Matters of Gravity

The Milky Way Galaxy

Galaxies

Quasars and Other Active Galaxies

Astrobiology

Filters

Exam 19: Cosmology

According to the current understanding of cosmology, what is the origin of the foamy structure of the universe, with clusters of galaxies distributed on the perimeters of voids?

What is the ratio of cosmic microwave background photons to hydrogen atoms, on average, in the universe?

The farther away a galaxy is, the more its light is redshifted, as observed from Earth. This relationship between redshift and distance is caused by

If astronomers could have turned a receiver toward the heavens in hopes of observing the cosmic microwave radiation 4.5 billion years ago, at the time the solar nebula was forming, what would they have found?

For any object moving uniformly, velocity = distance/time. So in the Hubble relationship for the expansion of the universe, v = H0r, what is the significance of the constant 1/H0?

In order to estimate the age of the universe as 1/H0 , astronomers must make a number of assumptions. Which of these is NOT one of the necessary assumptions?

Which one of these is NOT believed to be a characteristic of Population III stars?

The weak force

Consider a universe without dark energy (i.e., all the energy in the universe produces an attractive gravitational force). What will happen if the universe is closed?

Who discovered the cosmic microwave background radiation, the radiation left over from the Big Bang?

When did Einstein originally introduce his theory of general relativity, including the cosmological constant?

During what time interval was helium created in the Big Bang?

During the first millionth of a second in the history of the universe, a hydrogen nucleus could NOT exist. Why not?

When the universe was about 30,000 years old, the radiation density had decreased to the point where it was equal to the matter density. Yet it was only many years later that atoms formed. What happened to make possible the formation of atoms?

What is the "particle horizon"?

When astronomers view a distant quasar with highly redshifted emission lines in its spectrum, this wavelength shift is a

The Big Bang theory is the most widely accepted model of the early universe today. Which of these is NOT one of the reasons for this?

Suppose that the expansion rate were slower in the past. Taking this fact into account when estimating the age of the universe from the presently accepted value of the Hubble constant, H0 = 73.5 km/s/Mpc, yields

The Milky Way Galaxy is moving at about 600 km/s relative to the cosmic microwave background radiation. Why?

Discovering the Night Sky

Gravitation and the Motion of the Planets

Light and Telescopes

Atomic Physics and Spectra

Exoplanets and the Formation of Planetary Systems

Formation of the Solar System

Earth and the Moon

The Other Terrestrial Planets

The Outer Planets

Vagabonds of the Solar System

The Sun: Our Extraordinary Star

Characterizing Stars

The Lives of Stars From Birth Through Middle Age

The Death of Stars

Black Holes: Matters of Gravity

The Milky Way Galaxy

Galaxies

Quasars and Other Active Galaxies

Astrobiology

Filters

For any object moving uniformly, velocity = distance/time. So in the Hubble relationship for the expansion of the universe, v = H₀r, what is the significance of the constant 1/H₀?

In order to estimate the age of the universe as 1/H₀ , astronomers must make a number of assumptions. Which of these is NOT one of the necessary assumptions?

Suppose that the expansion rate were slower in the past. Taking this fact into account when estimating the age of the universe from the presently accepted value of the Hubble constant, H₀ = 73.5 km/s/Mpc, yields