Unformatted text preview: 1 Chapter 23 Post‐Lecture Quiz 1. Evidence that the cosmic background radiation really is the remnant of a Big Bang comes from predicting characteristics of remnant radiation from the Big Bang and comparing these predictions with observations. Four of the five statements below are real. Which one is fictitious? 1. The cosmic background radiation is expected to have a temperature just a few degrees above absolute zero, and its actual temperature turns out to be about 3 K (actually 2.7 K). 2. The cosmic background radiation is expected to have tiny temperature fluctuations at the level of about 1 part in 100,000. Such fluctuations were found in the COBE data. 3. The cosmic background radiation is expected to look essentially the same in all directions, and it does. 4. The cosmic background radiation is expected to have a perfect thermal spectrum, and observations from the COBE spacecraft verify this prediction. 5. The cosmic background radiation is expected to contain spectral lines of hydrogen and helium, and it does. 2. What are the slight fluctuations seen in maps of the cosmic background radiation? 1. Uncertainties in the map 2. Variations in the instrument’s sensitivity 3. The beginning of the formation of galaxies and clusters of galaxies 4. Dark matter 5. None of the above 3. What kinds of atomic nuclei formed during the era of nucleosynthesis? 1. only helium 2. nuclei of all the chemical elements 3. roughly equal amounts of each of the following: hydrogen, helium, lithium, beryllium, and boron 4. hydrogen and helium and trace amounts of lithium 5. only hydrogen 4. Olbers' paradox is an apparently simple question, but its resolution suggests that the universe is finite in age. What is the question? 1. Can we measure the position and momentum of an electron at the same time? 2. Why is the sky dark at night? 3. What would it be like to ride on a beam of light? 4. How many stars are in the universe? 5. How does the Sun produce energy? 2 5. The theory of inflation suggests that the structure of the universe may have originated as tiny quantum fluctuations. 1. Yes, tiny quantum fluctuations were stretched to enormous sizes by inflation and became large enough to grow into galaxies and galaxy clusters. 2. Yes, quantum uncertainty meant that some regions of the universe expanded more slowly than other regions and these slower moving regions eventually became galaxies and galaxy clusters. 3. No, the theory of inflation suggests that the structure of the universe arose when radiation decoupled from matter. 4. No, quantum fluctuations are on an atomic scale and the structure of the universe is on the scale of galaxies. 6. Why do we think tiny quantum ripples should have been present in the very early universe? 1. Matter and antimatter particles that spontaneously formed from high‐energy photons caused perturbations in the radiation field. 2. Quantum mechanics requires that the energy fields at any point in space be continually fluctuating as a result of the uncertainty principle. 3. The energy released when the strong force froze out of the GUT force caused shock waves that produced ripples in the universe. 4. The shock wave of the Big Bang caused ripples that expanded outward with time. 5. The annihilation of matter and antimatter particles caused tiny explosions that perturbed the radiation field. 7. Which of the following statements about the cosmic background radiation is not true? 1. It is the result of a mixture of radiation from many independent sources, such as stars and galaxies. 2. It has a temperature of about 3 degrees K above absolute zero. 3. It had a much higher temperature in the past. 4. It was discovered by Penzias and Wilson in the early 1960s. 5. It appears essentially the same in all directions (it is isotropic). 8. Why can't current theories describe what happened during the Planck era? 1. We do not know how much energy existed during that time. 2. We do not yet have a theory that links quantum mechanics and general relativity. 3. We do not understand the properties of antimatter. 4. The Planck era was the time before the Big Bang, and we cannot describe what happened before that instant. 3 9. Why is the era of nucleosynthesis so important in determining the chemical composition of the universe? 1. We can observe spectra from this era to determine what the primordial mix of the elements was at the beginning of the universe. 2. All the elements except hydrogen were produced after the era of nucleosynthesis. 3. We can study the processes that occurred during the era of nucleosynthesis to determine how most of the elements in the universe were created. 4. Except for the small amount of matter produced later by stars, the chemical composition of the universe is the same now as at the end of the era of nucleosynthesis. 5. By knowing how much matter was created during the era of nucleosynthesis, we can determine whether the universe is open or closed. 10. A GUT (grand unified theory) refers to theories that 1. unify the strong force and the electromagnetic and weak forces. 2. unify all four forces. 3. unify gravity and the electromagnetic and weak forces. 4. unify gravity and the strong and weak forces. 5. unify the electromagnetic and weak forces. 11. Although the universe today appears to be made mostly of matter and not antimatter, the Big Bang theory suggests that the very early universe had nearly equal amounts of matter and antimatter. 1. Yes, the Big Bang theory predicts that high temperatures in the early universe generated matter‐antimatter pairs, and the amounts of each were therefore virtually equal. 2. Yes, the Big Bang was started by the mutual annihilation of virtually equal numbers of matter and antimatter particles. 3. No, the amount of matter and antimatter in the early universe should be exactly the same as it is today. 4. No, the amount of matter and antimatter in the early universe should be in the same proportion as it is today. 12. Where do the photons in the cosmic background radiation originate? 1. the end of the era of nuclei 2. during the era of galaxy formation 3. the moment of the Big Bang 4. the end of the Planck era 5. during the era of nucleosynthesis 4 13. Helium originates from 1. stellar nucleosynthesis only. 2. mostly from the Big Bang with a small contribution from stellar nucleosynthesis. 3. mostly from stellar nucleosynthesis with a small contribution from the Big Bang. 4. radioactive decay of heavier elements only. 5. the Big Bang only. 14. Why did the era of nuclei end when the universe was about 300,000 years old? 1. The universe had expanded and cooled to a temperature of about 3,000 K, cool enough for stable, neutral atoms to form. 2. Neutrinos and electrons were finally able to escape the plasma of the early universe and no longer heated the otherparticles. 3. All the free particles had combined to form the nuclei of atoms. 4. No theory can explain this. 15. Which forces have physicists shown to be the same force under conditions of very high temperature or energy, as confirmed by experiments in particle accelerators? 1. the strong and weak forces 2. the strong and electromagnetic forces 3. gravity and the weak force 4. the electromagnetic and weak forces 5. gravity and the strong force 16. Some of the static “snow” (random noise) you see on an antenna‐fed TV (uses an antenna instead of satellite or cable) when it is not tuned to a broadcasting channel, is left over radiation from the Big Bang. 1. True 2. False 17. Why should it not be surprising that some galaxies contain little more than 25% helium, but it would be very surprising if some galaxies contained less. 1. Because a star converts about 25% of its hydrogen into helium before it dies. Galaxies with multiple generations of star formation can have a higher percentage. 2. Because the Big Bang fused 25% of normal matter in the universe into helium and stellar nucleosynthesis can increase, but not decrease, this amount. 3. The helium fraction decreases with age so younger galaxies have more than 25%, but galaxies with less helium would be older than the estimated age of the universe. 4. Helium is more massive than hydrogen so it cannot readily escape the gravitational field of a galaxy. A percentage lower than 25% would indicate that the galaxy had no dark matter. 5 18. When we say that the electromagnetic and weak forces "freeze out" from the electroweak force at 10 to power of ((‐10)) seconds after the Big Bang, we mean that 1. prior to this time the electromagnetic and weak forces maintained a single identity, but they possessed separate identities following this time. 2. following this time neither the electromagnetic nor the weak force was ever important in the universe again. 3. quantum fluctuations by high‐speed, relativistic particles in a state of false vacuum cause disturbances in the spacetime continuum, leading to the process described in the question this answer refers to. 4. "freezing out" was a term coined by particle physicists who think that the Big Bang theory is really cool. 5. these forces are important only at temperatures below the freezing point of water—a temperature that the universe reached at an age of about 10 to power of ((‐10)) second. 19. The Planck era refers to the time period 1. after the GUT era. 2. before the Planck time. 3. after the Planck time. 4. after inflation. 5. before the Big Bang. 20. Measuring the amount of deuterium in the universe allows us to set a limit on 1. the temperature of the universe at the end of the era of nuclei. 2. the density of ordinary (baryonic) matter in the universe. 3. the current age of the universe. 4. the total amount of mass in the universe. 5. the expansion rate of the universe. ...
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This note was uploaded on 03/03/2011 for the course RSM 100 taught by Professor Oesch during the Spring '08 term at University of Toronto.
- Spring '08