Question 1

The cosmic microwave background was discovered by

Accepted Answer

A)  rocket-borne telescopes that also discovered X-ray sources in space. 
B)  the Voyager 2 spacecraft during one of its "coasting" periods between planetary encounters. 
C)  scientists testing a new antenna and receiver for satellite communications. 
D)  the Infrared Astronomical Satellite (IRAS), which produced an all-sky infrared survey. 
A)  rocket-borne telescopes that also discovered X-ray sources in space. 
B)  the Voyager 2 spacecraft during one of its "coasting" periods between planetary encounters. 
C)  scientists testing a new antenna and receiver for satellite communications. 
D)  the Infrared Astronomical Satellite (IRAS), which produced an all-sky infrared survey.

Question 2

The effect that makes the cosmic microwave background appear slightly warmer in one direction and cooler in the opposite direction is

Accepted Answer

A)  a basic asymmetry in the background radiation, related to its origin. 
B)  the Doppler shift caused by motion of the Milky Way Galaxy through space toward the constellation Leo. 
C)  microwave emission from cool, primordial (pregalactic) clouds of gas and dust in that direction. 
D)  the presence of large clusters of galaxies in only one direction. 
A)  a basic asymmetry in the background radiation, related to its origin. 
B)  the Doppler shift caused by motion of the Milky Way Galaxy through space toward the constellation Leo. 
C)  microwave emission from cool, primordial (pregalactic) clouds of gas and dust in that direction. 
D)  the presence of large clusters of galaxies in only one direction.

Question 3

The cosmic microwave background radiation forms a blackbody curve corresponding to a temperature of 2.73 K. What does Wien's law predict for the peak wavelength in this blackbody curve?

Accepted Answer

A)  0.654 mm 
B)  1.07 mm 
C)  21.1 cm 
D)  2.73 m 
A)  0.654 mm 
B)  1.07 mm 
C)  21.1 cm 
D)  2.73 m

Question 4

Which of these statements BEST describes the history of the cosmological constant?

Accepted Answer

A)  Einstein introduced the constant to make the universe static, but many cosmologists now believe it makes the expansion of the universe accelerate. 
B)  Einstein introduced the constant to make the universe expand, and it is still necessary to cosmological theories today. 
C)  Einstein introduced the constant to make the universe static, but Hubble's discovery of the expanding universe proved that it the constant actually vanishes. 
D)  Einstein introduced the constant to make the universe expand, and it is now known that it has a much higher value today because the expansion is accelerating. 
A)  Einstein introduced the constant to make the universe static, but many cosmologists now believe it makes the expansion of the universe accelerate. 
B)  Einstein introduced the constant to make the universe expand, and it is still necessary to cosmological theories today. 
C)  Einstein introduced the constant to make the universe static, but Hubble's discovery of the expanding universe proved that it the constant actually vanishes. 
D)  Einstein introduced the constant to make the universe expand, and it is now known that it has a much higher value today because the expansion is accelerating.

Question 5

When Hubble did his early work on the expanding universe, he knew nothing about the cosmological redshift. He used the Doppler shift equations instead, but these gave him the correct answer. Why?

Accepted Answer

A)  These two sets of equations (Doppler shift and cosmological redshift) are the same and always give the same result for all cases. 
B)  Hubble was using only ordinary galaxies. If he had used galaxies with AGNs, the equations would not have worked. 
C)  Hubble was fortunate enough to use only galaxies for which the gravitational redshift and the cosmological redshift nearly cancel, so the Doppler shift provided essentially the whole effect. 
D)  Hubble was using only relatively nearby galaxies for which the nonrelativistic cosmological redshift and the Doppler shift provide the same result. 
A)  These two sets of equations (Doppler shift and cosmological redshift) are the same and always give the same result for all cases. 
B)  Hubble was using only ordinary galaxies. If he had used galaxies with AGNs, the equations would not have worked. 
C)  Hubble was fortunate enough to use only galaxies for which the gravitational redshift and the cosmological redshift nearly cancel, so the Doppler shift provided essentially the whole effect. 
D)  Hubble was using only relatively nearby galaxies for which the nonrelativistic cosmological redshift and the Doppler shift provide the same result.

Question 6

What is the range of the gravitational force (the maximum distance over which it acts)?

Accepted Answer

A)  1013 m, or roughly the size of the solar system 
B)  1021 m, or roughly the size of the Milky Way Galaxy 
C)  infinity 
D)  1026 m, or roughly the distance to the farthest quasars 
A)  1013 m, or roughly the size of the solar system 
B)  1021 m, or roughly the size of the Milky Way Galaxy 
C)  infinity 
D)  1026 m, or roughly the distance to the farthest quasars

Question 7

The predicted temperature of the early universe at which the four forces of nature would have been unified is

Accepted Answer

A)  1027 K. 
B)  1032 K. 
C)  106 K. 
D)  1015 K. 
A)  1027 K. 
B)  1032 K. 
C)  106 K. 
D)  1015 K.

Question 8

Why are the youngest galaxies that are seen in distant parts of the universe bluer and brighter than the older, closer galaxies observed?

Accepted Answer

A)  The red light has been partially absorbed by gas and dust between Earth and the galaxies. 
B)  Young galaxies have more dust, and dust scatters blue light better than red. 
C)  The light from the most distant galaxies has been bent by gravitational lenses and focused on Earth. 
D)  Young galaxies have a burst of star formation that produces many hot, bright, blue stars. 
A)  The red light has been partially absorbed by gas and dust between Earth and the galaxies. 
B)  Young galaxies have more dust, and dust scatters blue light better than red. 
C)  The light from the most distant galaxies has been bent by gravitational lenses and focused on Earth. 
D)  Young galaxies have a burst of star formation that produces many hot, bright, blue stars.

Question 9

Within the first second after the Big Bang, the universe was filled with high-energy, gamma-ray photons. These photons created huge numbers of elementary particles and their antiparticles through pair production. What happened to these particles?

Accepted Answer

A)  They are still here. They combined to create the first atoms and molecules that compose the physical universe. 
B)  The particles are still here as atoms and molecules, but almost all of the antiparticles disappeared. 
C)  The antiparticles annihilated with normal matter particles to produce more photons. 
D)  This pair production was followed by the era of cosmic inflation, during which these particles spread out to produce the matter densities that astronomers see today. 
A)  They are still here. They combined to create the first atoms and molecules that compose the physical universe. 
B)  The particles are still here as atoms and molecules, but almost all of the antiparticles disappeared. 
C)  The antiparticles annihilated with normal matter particles to produce more photons. 
D)  This pair production was followed by the era of cosmic inflation, during which these particles spread out to produce the matter densities that astronomers see today.

Question 10

Astronomer A claims that the Hubble constant is 84 km/s/Mpc, while astronomer B claims that it is 63 km/s/Mpc. The age of the universe calculated by astronomer A would be

Accepted Answer

A)  1.33 times the age calculated by astronomer B. 
B)  2/3 of the age calculated by astronomer B. 
C)  3/4 of the age calculated by astronomer B. 
D)  1.25 times the age calculated by astronomer B. 
A)  1.33 times the age calculated by astronomer B. 
B)  2/3 of the age calculated by astronomer B. 
C)  3/4 of the age calculated by astronomer B. 
D)  1.25 times the age calculated by astronomer B.

Question 11

The photons that enter microwave detectors today (and that astronomers interpret as the cosmic microwave background radiation) had their last interaction with matter

Accepted Answer

A)  at the instant of the Big Bang. 
B)  during the inflationary epoch. 
C)  during the era of recombination. 
D)  at the time of symmetry breaking. 
A)  at the instant of the Big Bang. 
B)  during the inflationary epoch. 
C)  during the era of recombination. 
D)  at the time of symmetry breaking.

Question 12

What is it that keeps localized regions of space, such as things on Earth, planetary systems, star clusters, and whole galaxies, from participating in the general expansion of the universe?

Accepted Answer

A)  their locations in places where irregularities in the chaotic Big Bang explosion permitted matter to condense 
B)  mutual gravitational attraction between objects in these systems 
C)  centrifugal force produced by the motion of the regions around a massive central object (e.g., the Sun, a supermassive black hole, etc.) 
D)  powerful and all-pervading gravitational pull from the central supermassive black holes of galaxies that holds everything in the galaxies in place 
A)  their locations in places where irregularities in the chaotic Big Bang explosion permitted matter to condense 
B)  mutual gravitational attraction between objects in these systems 
C)  centrifugal force produced by the motion of the regions around a massive central object (e.g., the Sun, a supermassive black hole, etc.) 
D)  powerful and all-pervading gravitational pull from the central supermassive black holes of galaxies that holds everything in the galaxies in place

Question 13

What is an advantage of quintessence over the cosmological constant as a description of dark energy?

Accepted Answer

A)  Einstein's reasoning in rejecting the cosmological constant still seems to be true today. 
B)  The cosmological constant would have to have, from the beginning of the universe, the right value to give a flat universe now: an amazing coincidence. The quintessence model does not have this requirement. 
C)  Quintessence is a well-established concept in physics, going back to ancient times, whereas the cosmological constant is a relatively new and untested concept. 
D)  The quintessence model predicts the correct age for the universe; the cosmological constant does not. 
A)  Einstein's reasoning in rejecting the cosmological constant still seems to be true today. 
B)  The cosmological constant would have to have, from the beginning of the universe, the right value to give a flat universe now: an amazing coincidence. The quintessence model does not have this requirement. 
C)  Quintessence is a well-established concept in physics, going back to ancient times, whereas the cosmological constant is a relatively new and untested concept. 
D)  The quintessence model predicts the correct age for the universe; the cosmological constant does not.

Question 14

Gravity holds galaxies together. What does the weak nuclear force hold together?

Accepted Answer

A)  leptons (particles including electrons and neutrinos) 
B)  nothing 
C)  nuclei 
D)  quarks inside protons and neutrons 
A)  leptons (particles including electrons and neutrinos) 
B)  nothing 
C)  nuclei 
D)  quarks inside protons and neutrons

Question 15

How do astronomers measure the relative amounts of dark matter and luminous matter in the early universe?

Accepted Answer

A)  The same way they do in the present universe: rotation curves, gravitational lensing, etc. 
B)  By measuring the sizes of the peaks created by acoustic waves in the cosmic microwave background. 
C)  By measuring the relative amplitudes in the acoustic overtone waves in the cosmic microwave background. 
D)  By measuring the relative frequencies in the acoustic overtone waves in the cosmic microwave background. 
A)  The same way they do in the present universe: rotation curves, gravitational lensing, etc. 
B)  By measuring the sizes of the peaks created by acoustic waves in the cosmic microwave background. 
C)  By measuring the relative amplitudes in the acoustic overtone waves in the cosmic microwave background. 
D)  By measuring the relative frequencies in the acoustic overtone waves in the cosmic microwave background.

Question 16

Suppose the universe contained only "normal" matter, like hydrogen, helium, etc. How would the expansion rate of the universe change with time?

Accepted Answer

A)  It would speed up. 
B)  It would slow down initially but then speed up when the matter pressure became high enough. 
C)  It would slow down. 
D)  It is impossible to tell, because it depends on the density of the matter. 
A)  It would speed up. 
B)  It would slow down initially but then speed up when the matter pressure became high enough. 
C)  It would slow down. 
D)  It is impossible to tell, because it depends on the density of the matter.

Question 17

Good evidence for an original Big Bang that "created" this universe comes from

Accepted Answer

A)  the rapid motions of some nearby stars, such as Barnard's Star. 
B)  a background "glow" of microwaves, with a blackbody temperature of about 3 K. 
C)  the measurement of the rotation of the Milky Way Galaxy. 
D)  the amount of gas and dust in the solar neighborhood. 
A)  the rapid motions of some nearby stars, such as Barnard's Star. 
B)  a background "glow" of microwaves, with a blackbody temperature of about 3 K. 
C)  the measurement of the rotation of the Milky Way Galaxy. 
D)  the amount of gas and dust in the solar neighborhood.

Question 18

What is the "electroweak" force?

Accepted Answer

A)  This is a fifth force, distinct from the original four, which helps to explain dark energy. 
B)  When charged particles of both signs (positive and negative) are closely mixed, the electromagnetic force-generally infinite in extent-is limited in its practical range. Under these circumstances, it is termed electroweak. 
C)  At sufficiently high temperatures the electromagnetic force and the weak nuclear force are indistinguishable. This composite force is called electroweak. 
D)  At sufficiently high temperature the strong nuclear force and gravitational force disappear. At even higher temperatures the weak nuclear force and the electromagnetic force combine to form the electroweak force. It is the only force that exists at this temperature. 
A)  This is a fifth force, distinct from the original four, which helps to explain dark energy. 
B)  When charged particles of both signs (positive and negative) are closely mixed, the electromagnetic force-generally infinite in extent-is limited in its practical range. Under these circumstances, it is termed electroweak. 
C)  At sufficiently high temperatures the electromagnetic force and the weak nuclear force are indistinguishable. This composite force is called electroweak. 
D)  At sufficiently high temperature the strong nuclear force and gravitational force disappear. At even higher temperatures the weak nuclear force and the electromagnetic force combine to form the electroweak force. It is the only force that exists at this temperature.

Question 19

When two high-energy gamma-ray photons collide, the gamma-ray photons could

Accepted Answer

A)  produce a huge number of low-energy photons. 
B)  disappear completely, leaving nothing behind. 
C)  disappear, creating a particle-antiparticle pair. 
D)  disappear, creating two negative electrons. 
A)  produce a huge number of low-energy photons. 
B)  disappear completely, leaving nothing behind. 
C)  disappear, creating a particle-antiparticle pair. 
D)  disappear, creating two negative electrons.

Question 20

Even though cosmic microwave background photons outnumber hydrogen atoms by about 1 billion to 1 in the universe, the universe is still considered to be matter-dominated because the

Accepted Answer

A)  photon energies are extremely small. 
B)  nature of the photons is such that they interact with nothing as they pass through the universe. 
C)  photons, while collectively carrying a large amount of energy, do not carry an equivalent amount of momentum and hence play little role in collisions with matter. 
D)  photons have no rest mass and hence can generate no gravity. 
A)  photon energies are extremely small. 
B)  nature of the photons is such that they interact with nothing as they pass through the universe. 
C)  photons, while collectively carrying a large amount of energy, do not carry an equivalent amount of momentum and hence play little role in collisions with matter. 
D)  photons have no rest mass and hence can generate no gravity.

The cosmic microwave background was discovered by

The effect that makes the cosmic microwave background appear slightly warmer in one direction and cooler in the opposite direction is

The cosmic microwave background radiation forms a blackbody curve corresponding to a temperature of 2.73 K. What does Wien's law predict for the peak wavelength in this blackbody curve?

Which of these statements BEST describes the history of the cosmological constant?

When Hubble did his early work on the expanding universe, he knew nothing about the cosmological redshift. He used the Doppler shift equations instead, but these gave him the correct answer. Why?

What is the range of the gravitational force (the maximum distance over which it acts)?

The predicted temperature of the early universe at which the four forces of nature would have been unified is

Why are the youngest galaxies that are seen in distant parts of the universe bluer and brighter than the older, closer galaxies observed?

Within the first second after the Big Bang, the universe was filled with high-energy, gamma-ray photons. These photons created huge numbers of elementary particles and their antiparticles through pair production. What happened to these particles?

Astronomer A claims that the Hubble constant is 84 km/s/Mpc, while astronomer B claims that it is 63 km/s/Mpc. The age of the universe calculated by astronomer A would be

The photons that enter microwave detectors today (and that astronomers interpret as the cosmic microwave background radiation) had their last interaction with matter

What is it that keeps localized regions of space, such as things on Earth, planetary systems, star clusters, and whole galaxies, from participating in the general expansion of the universe?

What is an advantage of quintessence over the cosmological constant as a description of dark energy?

Gravity holds galaxies together. What does the weak nuclear force hold together?

How do astronomers measure the relative amounts of dark matter and luminous matter in the early universe?

Suppose the universe contained only "normal" matter, like hydrogen, helium, etc. How would the expansion rate of the universe change with time?

Good evidence for an original Big Bang that "created" this universe comes from

What is the "electroweak" force?

When two high-energy gamma-ray photons collide, the gamma-ray photons could

Even though cosmic microwave background photons outnumber hydrogen atoms by about 1 billion to 1 in the universe, the universe is still considered to be matter-dominated because the

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

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Exam 19: Cosmology

The cosmic microwave background was discovered by

The effect that makes the cosmic microwave background appear slightly warmer in one direction and cooler in the opposite direction is

The cosmic microwave background radiation forms a blackbody curve corresponding to a temperature of 2.73 K. What does Wien's law predict for the peak wavelength in this blackbody curve?

Which of these statements BEST describes the history of the cosmological constant?

When Hubble did his early work on the expanding universe, he knew nothing about the cosmological redshift. He used the Doppler shift equations instead, but these gave him the correct answer. Why?

What is the range of the gravitational force (the maximum distance over which it acts)?

The predicted temperature of the early universe at which the four forces of nature would have been unified is

Why are the youngest galaxies that are seen in distant parts of the universe bluer and brighter than the older, closer galaxies observed?

Within the first second after the Big Bang, the universe was filled with high-energy, gamma-ray photons. These photons created huge numbers of elementary particles and their antiparticles through pair production. What happened to these particles?

Astronomer A claims that the Hubble constant is 84 km/s/Mpc, while astronomer B claims that it is 63 km/s/Mpc. The age of the universe calculated by astronomer A would be

The photons that enter microwave detectors today (and that astronomers interpret as the cosmic microwave background radiation) had their last interaction with matter

What is it that keeps localized regions of space, such as things on Earth, planetary systems, star clusters, and whole galaxies, from participating in the general expansion of the universe?

What is an advantage of quintessence over the cosmological constant as a description of dark energy?

Gravity holds galaxies together. What does the weak nuclear force hold together?

How do astronomers measure the relative amounts of dark matter and luminous matter in the early universe?

Suppose the universe contained only "normal" matter, like hydrogen, helium, etc. How would the expansion rate of the universe change with time?

Good evidence for an original Big Bang that "created" this universe comes from

What is the "electroweak" force?

When two high-energy gamma-ray photons collide, the gamma-ray photons could

Even though cosmic microwave background photons outnumber hydrogen atoms by about 1 billion to 1 in the universe, the universe is still considered to be matter-dominated because the

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