Question 1

Why are we so sure the early universe MUST have had some fluctuations in density?

Accepted Answer

A) The existence of galaxies shows empirically that these density fluctuations must have been present. Theoretically the early universe was expected to be perfectly smooth. 
B) These fluctuations are required by the Heisenberg uncertainty principle. 
C) Mutual gravitational attraction will always lead to lumpiness, even in a distribution that is perfectly uniform. 
D) This is related to the imbalance of matter and antimatter. This led to nonuniform annihilation reactions, and gravitational attraction led to collapse and lumpiness. 
A) The existence of galaxies shows empirically that these density fluctuations must have been present. Theoretically the early universe was expected to be perfectly smooth. 
B) These fluctuations are required by the Heisenberg uncertainty principle. 
C) Mutual gravitational attraction will always lead to lumpiness, even in a distribution that is perfectly uniform. 
D) This is related to the imbalance of matter and antimatter. This led to nonuniform annihilation reactions, and gravitational attraction led to collapse and lumpiness. B

Question 2

A supergrand unified theory (or theory of everything) would describe the physics of a universe in which what forces are unified?

Accepted Answer

A) all four 
B) everything except gravity 
C) the electromagnetic and weak forces 
D) the strong and weak forces 
A) all four 
B) everything except gravity 
C) the electromagnetic and weak forces 
D) the strong and weak forces A

Question 3

In what ways do the Kaluza-Klein multidimensional theories simplify our picture of the universe? Three of the following statements are correct. Which one is NOT a simplification of Kaluza-Klein theory?

Accepted Answer

A) In three space dimensions the trajectory of an object influenced by gravity appears straight, and in the multidimensional space of the Kaluza-Klein theory it appears straight. 
B) Many of the additional dimensions cancel out, leaving us with a simpler system than we had originally. 
C) Some dimensions in the multidimensional theory may not be observable because they are coiled tightly. 
D) We may be able to account for the existence of dark matter and dark energy. 
A) In three space dimensions the trajectory of an object influenced by gravity appears straight, and in the multidimensional space of the Kaluza-Klein theory it appears straight. 
B) Many of the additional dimensions cancel out, leaving us with a simpler system than we had originally. 
C) Some dimensions in the multidimensional theory may not be observable because they are coiled tightly. 
D) We may be able to account for the existence of dark matter and dark energy. B

Question 4

When the strong force is exerted between particles, these particles exchange:

Accepted Answer

A) gluons. 
B) intermediate vector bosons. 
C) gravitons. 
D) virtual photons. 
A) gluons. 
B) intermediate vector bosons. 
C) gravitons. 
D) virtual photons.

Question 5

In modern quantum physics, forces are manifested through the exchange of particles. Which one of the following is NOT one of these exchanged particles?

Accepted Answer

A) gluons 
B) virtual photons 
C) gravitons 
D) protons 
A) gluons 
B) virtual photons 
C) gravitons 
D) protons

Question 6

As the temperature in the early universe decreased, pair production reactions were confined to particles of smaller and smaller mass while annihilation reactions were unaffected. Why this difference?

Accepted Answer

A) Particles and antiparticles contain a certain amount of mass-energy independent of their temperature whereas the energy of a photon depends on its temperature. 
B) Photons contain a certain amount of mass-energy independent of their temperature whereas the energy of particles and antiparticles depend on its temperature. 
C) When particles collide, the interaction raises their temperature, but this does not happen when gamma-ray photons interact. 
D) When gamma-ray photons collide, the interaction raises their temperature, but this does not happen when particles interact. 
A) Particles and antiparticles contain a certain amount of mass-energy independent of their temperature whereas the energy of a photon depends on its temperature. 
B) Photons contain a certain amount of mass-energy independent of their temperature whereas the energy of particles and antiparticles depend on its temperature. 
C) When particles collide, the interaction raises their temperature, but this does not happen when gamma-ray photons interact. 
D) When gamma-ray photons collide, the interaction raises their temperature, but this does not happen when particles interact.

Question 7

Consider a density fluctuation around the era of recombination when the universe had a temperature of 3000 K. If the density fluctuation is about 10 ly across, will the matter within that fluctuation begin clumping together?

Accepted Answer

A) The Jeans length for these numbers is about 100 ly. Matter will not begin clumping together because there is not enough mass in the fluctuation of 10 ly to overcome the gas pressure. 
B) The Jeans length for these numbers is about 100 ly. Matter will begin clumping together since this is within the Jeans limit. 
C) The Jeans length for these numbers is about 1 ly. Matter will not begin clumping together because there is not enough mass in the fluctuation to overcome the gas pressure. 
D) The Jeans length for these numbers is about 1 ly. Matter will begin clumping together since this is within the Jeans limit. 
A) The Jeans length for these numbers is about 100 ly. Matter will not begin clumping together because there is not enough mass in the fluctuation of 10 ly to overcome the gas pressure. 
B) The Jeans length for these numbers is about 100 ly. Matter will begin clumping together since this is within the Jeans limit. 
C) The Jeans length for these numbers is about 1 ly. Matter will not begin clumping together because there is not enough mass in the fluctuation to overcome the gas pressure. 
D) The Jeans length for these numbers is about 1 ly. Matter will begin clumping together since this is within the Jeans limit.

Question 8

The inflationary epoch required an enormous amount of energy. What was the source of this energy?

Accepted Answer

A) The universe cooled as it expanded, releasing energy. 
B) The universe made the transition from the false vacuum to the true vacuum, releasing energy. 
C) The particles gained energy in the form of mass from the Higgs field. 
D) Gravitons, released by the newly created gravitational field, provided energy. 
A) The universe cooled as it expanded, releasing energy. 
B) The universe made the transition from the false vacuum to the true vacuum, releasing energy. 
C) The particles gained energy in the form of mass from the Higgs field. 
D) Gravitons, released by the newly created gravitational field, provided energy.

Question 9

In modern quantum physics, the Heisenberg uncertainty principle states that the more precisely you know a particle's:

Accepted Answer

A) velocity, the more certain you are of its position in space. 
B) mass, the less certain you are of its size. 
C) position, the more certain you are of its speed and motion. 
D) position, the less certain you are of its speed and motion. 
A) velocity, the more certain you are of its position in space. 
B) mass, the less certain you are of its size. 
C) position, the more certain you are of its speed and motion. 
D) position, the less certain you are of its speed and motion.

Question 10

Consider a large cloud of hydrogen gas, all at a uniform temperature. How do density fluctuations within this cloud affect its tendency to collapse gravitationally?

Accepted Answer

A) In those regions where the density is larger the gas pressure will also be larger, and the gas will be less likely to collapse. 
B) In those regions where the density is larger the Jeans length is smaller, meaning that smaller regions of the gas are likely to collapse. 
C) The Jeans length must be calculated for the entire cloud. Density fluctuations within the cloud have no effect. 
D) The likelihood of gravitational collapse cannot be calculated from the information given. 
A) In those regions where the density is larger the gas pressure will also be larger, and the gas will be less likely to collapse. 
B) In those regions where the density is larger the Jeans length is smaller, meaning that smaller regions of the gas are likely to collapse. 
C) The Jeans length must be calculated for the entire cloud. Density fluctuations within the cloud have no effect. 
D) The likelihood of gravitational collapse cannot be calculated from the information given.

Question 11

In the present universe there is an imbalance between particles and antiparticles. How did this originate?

Accepted Answer

A) It is believed that there are slight differences in mass between matter and antimatter. Thus the inflationary epoch, which gave mass and energy to the universe, created an imbalance of particles. 
B) It is believed that there are slight differences in electric charge between matter and antimatter. Thus the inflationary epoch, which gave mass and energy to the universe, created an imbalance of particles. 
C) We see only a small part of the universe. The missing antimatter is elsewhere, repelled by the negative mass of normal matter early in the history of the universe. 
D) This question is an unsolved mystery of present-day cosmology. 
A) It is believed that there are slight differences in mass between matter and antimatter. Thus the inflationary epoch, which gave mass and energy to the universe, created an imbalance of particles. 
B) It is believed that there are slight differences in electric charge between matter and antimatter. Thus the inflationary epoch, which gave mass and energy to the universe, created an imbalance of particles. 
C) We see only a small part of the universe. The missing antimatter is elsewhere, repelled by the negative mass of normal matter early in the history of the universe. 
D) This question is an unsolved mystery of present-day cosmology.

Question 12

Quantum electrodynamics describes forces in terms of the exchange of particles. The electromagnetic force, for example, involves the exchange of virtual photons. The weak force involves the exchange of:

Accepted Answer

A) gluons. 
B) intermediate vector bosons. 
C) gravitons. 
D) virtual neutrinos. 
A) gluons. 
B) intermediate vector bosons. 
C) gravitons. 
D) virtual neutrinos.

Question 13

Arrange the following particles in order of increasing threshold temperature.

Accepted Answer

A) electron, proton, neutrino, and neutron 
B) neutrino, neutron, electron, and proton 
C) neutrino, electron, proton, and neutron 
D) proton, electron, neutron, and neutrino 
A) electron, proton, neutrino, and neutron 
B) neutrino, neutron, electron, and proton 
C) neutrino, electron, proton, and neutron 
D) proton, electron, neutron, and neutrino

Question 14

During the period of cosmic inflation, the universe underwent an extremely rapid expansion, increasing its size by a factor of 1050 in a time of perhaps 10-32 seconds. Did this action violate the postulate of special relativity that nothing can travel faster than the speed of light?

Accepted Answer

A) Yes, but this was before the Planck time, and the laws of physics as we presently understand them, including the laws of special relativity, did not yet apply. 
B) No. The universe was so small at the beginning of the inflationary epoch that even an expansion by 50 orders of magnitude did not take it far enough in 10-32 seconds to exceed the speed of light. 
C) The postulate of special relativity was not violated because it was the dimensions of space that were expanding. The postulate applies to objects moving through space. 
D) The postulate of special relativity was not violated because the curvature of space was so extreme at this time that the distance objects moved through during this 10-32 seconds was foreshortened so that the speed was less than the speed of light. 
A) Yes, but this was before the Planck time, and the laws of physics as we presently understand them, including the laws of special relativity, did not yet apply. 
B) No. The universe was so small at the beginning of the inflationary epoch that even an expansion by 50 orders of magnitude did not take it far enough in 10-32 seconds to exceed the speed of light. 
C) The postulate of special relativity was not violated because it was the dimensions of space that were expanding. The postulate applies to objects moving through space. 
D) The postulate of special relativity was not violated because the curvature of space was so extreme at this time that the distance objects moved through during this 10-32 seconds was foreshortened so that the speed was less than the speed of light.

Question 15

The proposed inflationary epoch would explain many features of the observable universe. But can inflation itself be tested?

Accepted Answer

A) No, unfortunately there is no direct test for inflation. 
B) Yes, the temperature of the cosmic microwave background provides a test of cosmic inflation. 
C) Yes, the uniformity of the cosmic microwave background provides a test of cosmic inflation. 
D) Yes, the polarization of the cosmic microwave background provides a test of cosmic inflation. 
A) No, unfortunately there is no direct test for inflation. 
B) Yes, the temperature of the cosmic microwave background provides a test of cosmic inflation. 
C) Yes, the uniformity of the cosmic microwave background provides a test of cosmic inflation. 
D) Yes, the polarization of the cosmic microwave background provides a test of cosmic inflation.

Question 16

If the average mass density ρ0 had been greater than the critical density ρc in the early universe, what might have been the likely result?

Accepted Answer

A) The universe would have expanded very rapidly, and matter would not have clumped together to form galaxies. 
B) The universe's mass would have clumped together in a relatively short time and collapsed to a singularity like that from which it emerged. 
C) Cosmic inflation would not have occurred. 
D) The cosmic microwave background radiation would not have been created. 
A) The universe would have expanded very rapidly, and matter would not have clumped together to form galaxies. 
B) The universe's mass would have clumped together in a relatively short time and collapsed to a singularity like that from which it emerged. 
C) Cosmic inflation would not have occurred. 
D) The cosmic microwave background radiation would not have been created.

Question 17

Which one of the following statements correctly describes a major difference between galaxy formation with cold dark matter and galaxy formation with hot dark matter?

Accepted Answer

A) In both cases, galaxies form by the breakup of larger objects, but the breakup occurs faster if the dark matter is hot than if it is cold. 
B) With cold dark matter, galaxies form by the breakup of larger objects, whereas with hot dark matter galaxies form through the merger of smaller objects. 
C) In both cases, galaxies form through the merger of smaller objects, but the merger occurs faster if the dark matter is cold than if it is hot. 
D) With cold dark matter, galaxies form through the merger of smaller objects, whereas with hot dark matter, galaxies form by the breakup of larger objects. 
A) In both cases, galaxies form by the breakup of larger objects, but the breakup occurs faster if the dark matter is hot than if it is cold. 
B) With cold dark matter, galaxies form by the breakup of larger objects, whereas with hot dark matter galaxies form through the merger of smaller objects. 
C) In both cases, galaxies form through the merger of smaller objects, but the merger occurs faster if the dark matter is cold than if it is hot. 
D) With cold dark matter, galaxies form through the merger of smaller objects, whereas with hot dark matter, galaxies form by the breakup of larger objects.

Question 18

Within which time interval from the initial Big Bang do we believe all four fundamental forces of nature were united into a single force?

Accepted Answer

A) t = 0 to 10-43 second, the Planck time, when gravity "froze out" of the universe 
B) t = 0 to 106 years, when radiation dominated the universe 
C) t = 0 to 10-35 second, when the strong nuclear force "froze out" of the universe 
D) t = 0 to 1 second, when photons interchanged freely with electron-positron pairs 
A) t = 0 to 10-43 second, the Planck time, when gravity "froze out" of the universe 
B) t = 0 to 106 years, when radiation dominated the universe 
C) t = 0 to 10-35 second, when the strong nuclear force "froze out" of the universe 
D) t = 0 to 1 second, when photons interchanged freely with electron-positron pairs

Question 19

After about 2 seconds, the early universe contained almost no neutrons. But protons remained. Why this difference?

Accepted Answer

A) Neutrons are much more massive than protons. After the first 2 seconds the temperature of the universe had fallen below the threshold for pair production of neutrons but not of protons. 
B) Neutrons, being uncharged, can get close to other particles and annihilate them. Protons, being charged, cannot get close to other particles. 
C) Free neutrons decay spontaneously. Free protons are stable. 
D) Virtual proton-antiproton pairs were produced during the inflationary period, but neutral neutrons have no antiparticles and thus were not pair produced. 
A) Neutrons are much more massive than protons. After the first 2 seconds the temperature of the universe had fallen below the threshold for pair production of neutrons but not of protons. 
B) Neutrons, being uncharged, can get close to other particles and annihilate them. Protons, being charged, cannot get close to other particles. 
C) Free neutrons decay spontaneously. Free protons are stable. 
D) Virtual proton-antiproton pairs were produced during the inflationary period, but neutral neutrons have no antiparticles and thus were not pair produced.

Question 20

When we apply the Jeans length criterion to the conditions of the early universe, it is found that the structures most likely to have formed first are:

Accepted Answer

A) long filaments of galaxies. 
B) individual spiral galaxies. 
C) individual elliptical galaxies. 
D) globular clusters. 
A) long filaments of galaxies. 
B) individual spiral galaxies. 
C) individual elliptical galaxies. 
D) globular clusters.

Exam 26: Exploring the Early Universe

Why are we so sure the early universe MUST have had some fluctuations in density?

A supergrand unified theory (or theory of everything) would describe the physics of a universe in which what forces are unified?

In what ways do the Kaluza-Klein multidimensional theories simplify our picture of the universe? Three of the following statements are correct. Which one is NOT a simplification of Kaluza-Klein theory?

When the strong force is exerted between particles, these particles exchange:

In modern quantum physics, forces are manifested through the exchange of particles. Which one of the following is NOT one of these exchanged particles?

As the temperature in the early universe decreased, pair production reactions were confined to particles of smaller and smaller mass while annihilation reactions were unaffected. Why this difference?

Consider a density fluctuation around the era of recombination when the universe had a temperature of 3000 K. If the density fluctuation is about 10 ly across, will the matter within that fluctuation begin clumping together?

The inflationary epoch required an enormous amount of energy. What was the source of this energy?

In modern quantum physics, the Heisenberg uncertainty principle states that the more precisely you know a particle's:

Consider a large cloud of hydrogen gas, all at a uniform temperature. How do density fluctuations within this cloud affect its tendency to collapse gravitationally?

In the present universe there is an imbalance between particles and antiparticles. How did this originate?

Quantum electrodynamics describes forces in terms of the exchange of particles. The electromagnetic force, for example, involves the exchange of virtual photons. The weak force involves the exchange of:

Arrange the following particles in order of increasing threshold temperature.

During the period of cosmic inflation, the universe underwent an extremely rapid expansion, increasing its size by a factor of 1050 in a time of perhaps 10-32 seconds. Did this action violate the postulate of special relativity that nothing can travel faster than the speed of light?

The proposed inflationary epoch would explain many features of the observable universe. But can inflation itself be tested?

If the average mass density ρ0 had been greater than the critical density ρc in the early universe, what might have been the likely result?

Which one of the following statements correctly describes a major difference between galaxy formation with cold dark matter and galaxy formation with hot dark matter?

Within which time interval from the initial Big Bang do we believe all four fundamental forces of nature were united into a single force?

After about 2 seconds, the early universe contained almost no neutrons. But protons remained. Why this difference?

When we apply the Jeans length criterion to the conditions of the early universe, it is found that the structures most likely to have formed first are:

Astronomy and the Universe

Knowing the Heavens

Eclipses and the Motion of the Moon

Gravitation and the Waltz of the Planets

The Nature of Light

Optics and Telescopes

Comparative Planetology I: Our Solar System

Comparative Planetology II: the Origin of Our Solar System

The Living Earth

Our Barren Moon

Mercury, Venus, and Mars: Terrestrial, yet Unique

Jupiter and Saturn: Lords of the Planets

Jupiter and Saturns Satellites of Fire and Ice

Uranus, Neptune, Pluto, and the Kuiper Belt: Remote Worlds

Asteroids, Comets, and Impacts

Our Star, the Sun

The Nature of the Stars

The Birth of Stars

Stellar Evolution: on and After the Main Sequence

Stellar Evolution: The Death of Stars

Stellar Remnants: Neutron Stars and Black Holes

Our Galaxy

Galaxies

Quasars and Active Galaxies

Cosmology: The Origin and Evolution of the Universe

The Search for Extraterrestrial Life

Filters

During the period of cosmic inflation, the universe underwent an extremely rapid expansion, increasing its size by a factor of 10⁵⁰ in a time of perhaps 10^-32 seconds. Did this action violate the postulate of special relativity that nothing can travel faster than the speed of light?

If the average mass density ρ₀ had been greater than the critical density ρ_c in the early universe, what might have been the likely result?