A) energy.
B) mass.
C) charge.
D) strangeness.
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A) They are not actually particles, but just points in space.
B) Extremely high energies are needed to create these particles.
C) The fundamental strings that make up these particles vibrate at frequencies we cannot detect.
D) The particles do not exist in three-dimensional space.
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A) the change of one type of quark into another type of quark into another type of quark by the weak force
B) the interactions of charged particles by the exchange of virtual photons
C) the bonding between quarks by the exchange of gluons
D) the interactions of nuclear particles by the strong force
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A) Deuterium had to form before helium could form, but deuterium is easily destroyed, thus preventing the formation of helium.
B) Deuterium absorbs neutrons efficiently, thus producing heavier and heavier isotopes of hydrogen instead of heavier elements such as helium.
C) Deuterium had to form before helium could form, but deuterium is almost impossible to create, thus preventing the formation of helium.
D) Helium is used up in the formation of deuterium. However, deuterium is difficult to create, thus leaving us with large amounts of helium.
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A) No, never. Matter is a form of energy, and the spontaneous creation of matter would violate conservation of energy.
B) Yes, but only for extremely short times.
C) Yes, but only if the particles created are electrically neutral.
D) Yes, but only if an equal amount of matter disappears from some other part of the universe.
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A) by nuclear reactions in the cores of stars, and was then thrown out into space by supernovae
B) by the collision of cosmic rays with hydrogen nuclei in interstellar gas clouds
C) by high-energy processes during the collapse of protogalactic clouds during the formation of galaxies
D) by nuclear reactions during the Big Bang
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A) whether dark matter is hot or cold, cold dark matter resulting in the top-down scenario
B) whether dark matter is hot or cold, hot dark matter resulting in the top-down scenario
C) whether neutrinos have mass, massless neutrinos resulting in the top-down scenario
D) whether the early universe had an abundance or a scarcity of metals, an abundance resulting in the bottom-up scenario
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A) immediately, as they were a direct product of the Big Bang
B) about 380,000 years later
C) about 400 million years later
D) not until about 3.2 billion years later
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A) during the first 300,000 years
B) during the first 10-43 second
C) during the first 10-6 second
D) during the first 15 minutes
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A) No, this was not really necessary. Witten was attempting to recast the theory to make its connections with general relativity more apparent.
B) Yes, this was necessary. Mistakes had been found in the earlier theory, and additional dimensions seemed the easiest way to fix these.
C) Yes, this was necessary. Between Kaluza and Witten, two additional forces had been discovered, and the natural solution was to add more dimensions to the theory.
D) Yes, this was necessary. Witten's extra dimensions were specifically an attempt to account for dark matter.
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A) They were created during the cosmic singularity and bounced around until the universe became transparent to radiation.
B) They were given off when the free electrons were captured by protons to form the first hydrogen atoms.
C) As the universe expanded and the radiation cooled, photons no longer had enough energy to create particles by pair production. But particles continued to annihilate and produce additional photons.
D) The "fireball" that we see in the distant past is really a reflection of all the radiation produced before that time bouncing back from the universe in its early opaque state.
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A) The cosmic microwave background itself caused the reionization of hydrogen and helium.
B) Large, hot Population III stars emitted enough high-energy radiation during their lifetimes to cause reionization.
C) The intense background of neutrinos and antineutrinos released much earlier than the cosmic microwave background radiation had enough energy to cause reionization.
D) The explosions of giant Population III stars would cause a shower of high-speed particles that could result in reionization.
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A) 1:10
B) 1:6
C) 1:4
D) 1:1
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A) Because it is a particle with mass, its speed is governed by the temperature of its surroundings because it will always be in thermal equilibrium.
B) Because it is a particle with mass, its speed must be less than the speed of light, c.
C) Its speed must be faster than the speed of light, because this is the only way that a lepton can have mass.
D) Because of its nature, a neutrino can only exist when it is traveling at the speed of light, just like photons of electromagnetic radiation.
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A) It took whatever curvature the early universe had and flattened it.
B) The epoch allowed the early, preinflationary universe to be very small and thus capable of thermal equalization.
C) It permitted matter to move faster than the speed of light for a brief period.
D) It forced the observed density of the universe to be equal to the critical density to great precision.
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A) 3.5 × 10-25 s
B) 1.1 × 10-16 s
C) 2.2 × 10-16 s
D) 7.0 × 10-27 s
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A) 2 × 10-27 kg, about the mass of one hydrogen atom
B) 10-19 kg
C) about 1 kg
D) 2 × 1030 kg, about the mass of the Sun
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A) As the universe expanded rapidly, it cooled rapidly. Thereafter it expanded and cooled at a more moderate rate.
B) Because of the incredible speed of the expansion, there was no time for particles to exchange energy. Thus, the temperature remained constant during the expansion.
C) Because of the tremendous amount of energy available, the temperature actually rose during the expansion.
D) The temperature decreased during the expansion and then rose again to essentially the value it had initially.
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A) The range of the strong nuclear force is 10 times smaller than the size of an atomic nucleus.
B) The range of the strong nuclear force is infinite; it has no limit.
C) The range of the strong nuclear force is the same as the size of the nucleus.
D) The range of the strong nuclear force is 10 times larger than the size of an atomic nucleus.
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A) The first generation of stars had lower metallicity than the present generation, but in each era the formation of large stars and small stars was equally likely.
B) It is easier to make a gas and dust cloud collapse when the metal content is low. Thus, even small stars could be formed in the early universe, but large stars were a rarity.
C) It is harder to make a gas and dust cloud collapse when the metal content is low. Thus, even small stars could be formed in the early universe, but large stars were a rarity.
D) It is harder to make a gas and dust cloud collapse when the metal content is low. Thus, large stars were more likely to be formed in the early universe, but small stars were a rarity.
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