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COBE found that the cosmic background radiation has a perfect thermal radiation spectrum, with a peak corresponding to a temperature of 2.73 K. However, it also found slight fluctuations in the radiation. The temperature varies very slightly from one place to another by a few parts in 100,000.
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A) mostly from stellar nucleosynthesis with a small contribution from the Big Bang.
B) radioactive decay of elements heavier than carbon.
C) stellar nucleosynthesis only.
D) mostly from the Big Bang with a small contribution from stellar nucleosynthesis.
E) the Big Bang only.
G) C) and D)
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B) False
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A) There would have needed to be ionized hydrogen (which would contradict the idea that the CMB originates at the time the universe cooled enough for protons and electrons to combine, making neutral atoms) .
B) There would have needed to be cooler hydrogen clouds (which would contradict the observation of a uniform temperature in all directions) .
C) There would have needed to be even warmer hydrogen clouds (which would contradict the observation of a uniform temperature in all directions) .
E) A) and C)
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Hubble's discovery showed that the unive...View Answer
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A) The expanding universe would have cooled.
B) Matter was near the critical- density for a universal collapse, which smoothed out the differences in temperatures.
C) Prior to rapid inflation, all regions of space were close enough to bounce radiation back- and- forth and reach the same temperature.
D) Matter expanded into regions of space that had no matter, and thus ended up at the same temperature.
F) A) and B)
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A) It marks the time at which the first stars formed.
B) The basic chemical composition of the universe had been determined.
C) The proportions of dark matter and luminous matter had been determined.
D) It marks the time at which the expansion of the universe had settled down to its current rate.
F) A) and B)
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A) the predominance of matter over antimatter and the near- critical density of the universe
B) the cosmic background radiation and the near- critical density of the universe
C) the cosmic background radiation and the expansion of the universe
D) the cosmic background radiation and the helium content of the universe
E) the predominance of matter over antimatter and the large scale structure of the universe
G) B) and D)
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A) 1 force that represented the unification of all four forces that operate today
B) 2 forces: the strong force and the electroweak force
C) 3 forces: gravity, the strong force, and the electroweak force
D) 2 forces: gravity and a single force that later became the strong, weak, and electromagnetic forces
F) B) and D)
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A) the discovery of two galaxies at the same distance, moving away with slightly different speeds
B) the discovery of a galaxy moving toward us
C) the discovery that the temperature of the universe is only 2.73 K
D) the discovery of a galaxy with 10% helium abundance
E) the discovery of a galaxy with 30% helium abundance
G) B) and C)
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A) before the Planck time.
B) after the GUT era.
C) before the Big Bang.
D) after inflation.
E) after the Planck time.
G) B) and C)
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A
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A) The electromagnetic force only works on scales of about an atomic nucleus.
B) Most objects are electrically neutral.
C) Electrical charge is canceled out by mass.
D) The electromagnetic force follows an inverse cube law with distance, rather than an inverse square law.
F) None of the above
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In the steady state universe hypothesis,...View Answer
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A) They combined in groups to make protons, neutrons, and their antiparticles.
B) They evaporated.
C) They froze out of the soup of particles at the end of the era.
D) They combined in groups to make electrons and neutrinos.
F) B) and C)
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B) False
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The era of nucleosynthesis is important because during this time, all the primordial hydrogen and helium was created by nuclear fusion. Except for the few percent of matter that stars later fused into heavier elements, the chemical composition set in the nucleosynthesis era remains unchanged today.
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A) The universe had expanded and cooled enough for stable, neutral atoms to form.
B) The nucleosynthesis era that produced the nuclei heavier than helium ended.
C) All the free particles had combined to form the nuclei of atoms.
D) Atomic nuclei were finally able to escape the plasma of the early universe.
E) Photons were finally able to escape the plasma of the early universe and were no longer available to produce hydrogen and helium nuclei.
G) D) and E)
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B) False
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B) False
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A) Temperatures in the early universe were never above the roughly 100 million Kelvin required for helium fusion.
B) Helium fusion occurred, but the carbon nuclei that were made were later destroyed by the intense radiation in the early universe.
C) By the time stable helium nuclei had formed, the temperature and density had already dropped too low for helium fusion to occur.
D) No one knows-this is one of the major mysteries in astronomy.
F) None of the above
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