Chapter 29 Big Bang Cosmology
11) Which of the following statements best summarizes current evidence concerning dark matter in individual galaxies and in clusters of galaxies? A) Dark matter is the dominant form of mass in both clusters and in individual galaxies. B) Dark matter is present between galaxies in clusters, but not within individual galaxies. C) Dark matter is present in individual galaxies, but there is no evidence that it can exist between the galaxies in a cluster. D) Within individual galaxies, dark matter is always concentrated near the galactic center, and within clusters it is always concentrated near the cluster center.
Answer: A
12) Based on current evidence, a supercluster is most likely to have formed in regions of space where A) the density of dark matter was slightly higher than average when the universe was very young. B) there was an excess concentration of hydrogen gas when the universe was very young. C) supermassive black holes were present in the very early universe. D) the acceleration of the expansion was proceeding faster than elsewhere.
Answer: A
12) Which of the following observations cannot be explained by the Big Bang theory unless we assume that an episode of inflation occurred? A) the fact that the temperature of the cosmic microwave background is almost the same everywhere B) the fact that about 25% of the ordinary matter in the universe consists of helium C) the existence of the cosmic microwave background D) the fact that the universe is expanding
Answer: A
13) Compared to the central regions of spiral galaxies, we expect elliptical galaxies to have A) higher mass-to-light ratios because stars in elliptical galaxies are dimmer than those in spirals. B) lower mass-to-light ratios because stars in elliptical galaxies are dimmer than those in spirals. C) higher mass-to-light ratios because stars in elliptical galaxies do not have high orbital velocities. D) lower mass-to-light ratios because elliptical galaxies have less gas and dust than spirals. E) the same mass-to-light ratio because they are made of the same material, stars and dark matter.
Answer: A
13) What happened to the quarks that existed freely during the particle era? A) They combined in groups to make protons, neutrons, and their antiparticles. B) They froze out of the soup of particles at the end of the era. C) They evaporated. D) They combined in groups to make electrons and neutrinos. E) They combined in groups to make W and Z bosons.
Answer: A
14) Which of the following best sums up current scientific thinking about the nature of dark matter? A) Most dark matter probably consists of weakly interacting particles of a type that we have not yet identified. B) Dark matter consists 90% of neutrinos and 10% of WIMPs. C) There is no longer any doubt that dark matter is made mostly of WIMPs. D) Dark matter probably does not really exist, and rather indicates a fundamental problem in our understanding of gravity.
Answer: A
15) What is the temperature of the universe (as a whole) today? A) 3K B) 300K C) 3000K D) The universe cannot be said to have a single temperature.
Answer: A
16) The critical density of the universe is the A) average density the universe would need for gravity to someday halt the current expansion if dark energy did not exist. B) actual average density of the universe. C) density of dark matter in the universe. D) density of water.
Answer: A
18) Gravitational lensing occurs when A) massive objects bend light beams that are passing nearby. B) massive objects cause more distant objects to appear much larger than they should and we can observe the distant objects with better resolution. C) dark matter builds up in a particular region of space, leading to a very dense region and an extremely high mass-to-light ratio. D) telescope lenses are distorted by gravity.
Answer: A
2) Which of the following best summarizes what we mean by dark energy? A) It is a name given to whatever is causing the expansion of the universe to accelerate with time. B) It is the energy contained in dark matter. C) It is the energy of black holes. D) It is a type of energy that is associated with the "dark side" of The Force that rules the cosmos.
Answer: A
21) Which of the following is an example of baryonic matter? A) you B) the particles produced by physicists in particle accelerators C) electrons and positrons produced by pair production D) WIMPs E) neutrinos
Answer: A
21) Why does the Big Bang theory predict that the cosmic background radiation should have a perfect thermal radiation spectrum? A) The background radiation came from the heat of the universe, with a peak corresponding to the temperature of the universe. B) The spectrum of pure hydrogen is a perfect thermal radiation spectrum. C) The spectrum of 75 percent hydrogen and 25 percent helium is a perfect thermal radiation spectrum. D) The light from all the stars and gas in the sky averaged over the entire universe is a perfect thermal radiation spectrum. E) It doesn't predict that the cosmic background radiation should have a perfect thermal radiation spectrum.
Answer: A
22) Why do we expect the cosmic background radiation to be almost, but not quite, the same in all directions? A) The overall structure of the universe is very uniform, but the universe must have contained some regions of higher density in order for galaxies to form. B) The temperature of the universe can be found by taking an average over the entire sky, but individual stars will create peaks in the spectrum over small angles. C) Dark matter consisting of WIMPs greatly smooths out the spectrum, but the small patches of "light" matter create peaks in the spectrum. D) The overall structure of the universe is very uniform, but the synthesis of different elements produces varying signatures within the background spectrum. E) The overall structure of the universe is very uniform, but intervening gas between us and the era of nuclei absorbs wavelengths depending on the composition and redshift of the gas.
Answer: A
24) What are the two key observational facts that led to widespread acceptance of the Big Bang model? A) the cosmic background radiation and the high helium content of the universe B) the cosmic background radiation and the expansion of the universe C) the cosmic background radiation and the near-critical density of the universe D) the predominance of matter over antimatter and the near-critical density of the universe E) the predominance of matter over antimatter and the large scale structure of galaxies
Answer: A
3) Spiral galaxy rotation curves are generally fairly flat out to large distances. Suppose that spiral galaxies did not contain dark matter. How would their rotation curves be different? A) The orbital speeds would fall off sharply with increasing distance from the galactic center. B) The orbital speeds would rise upward with increasing distance from the galactic center, rather than remaining approximately constant. C) The rotation curve would be a straight, upward sloping diagonal line, like the rotation curve of a merry-go-round. D) The rotation curve would look the same with or without the presence of dark matter.
Answer: A
3) Which of the following statements best explains what we mean when we say that the electroweak and strong forces "froze out" at 10-38 second after the Big Bang? A) These two forces first became distinct at this time. B) These forces are important only at temperatures below the freezing point of water—a temperature that the universe reached at an age of about at 10-38 second. C) Freezing out was a term coined by particle physicists who think that the Big Bang theory is really cool. D) Following this time, neither the strong nor electroweak forces were ever important in the universe again.
Answer: A
2) Although most astronomers assume dark matter really exists, there is at least one other possible explanation for the phenomena attributed to dark matter. What is it? A) The so-called dark matter is really just ordinary stars that are enshrouded in clouds of dust. B) There could be something wrong or incomplete with our understanding of how gravity operates on galaxy-size scales. C) There could be something wrong with our understanding of how atoms produce light. D) We could just be having a hard time understanding the observations because they involve very distant galaxies.
Answer: B
2) What happens when a particle of matter meets its corresponding antiparticle of antimatter? A) They can form a complete atom. B) The combined mass of the two particles is completely transformed into energy (photons). C) They fuse to make a heavier particle. D) The question makes no sense, since antimatter does not really exist.
Answer: B
24) What do we mean when we say that a particle is a weakly interacting particle? A) It interacts only through the weak force. B) It interacts only through the weak force and the force of gravity. C) It is so small that it doesn't affect objects in the universe. D) It doesn't interact with any type of baryonic matter. E) It is the only type of particle that interacts through the weak force.
Answer: B
3) The Planck era refers to the time period A) before the Big Bang. B) before the Planck time. C) after the Planck time. D) after inflation. E) after the GUT era.
Answer: B
3) What is the significance of the Planck time? A) It is the time at which inflation is thought to have occurred. B) Before it, conditions were so extreme that our current understanding of physics is insufficient to predict what might have occurred. C) It is the time when the cosmic microwave background was released. D) It is the amount of time required for two protons to fuse to make deuterium.
Answer: B
30) What do peculiar velocities reveal? A) the amount of dark matter in a galaxy B) the distribution of dark matter in large-scale structures C) the composition of dark matter D) the error in our observations of Hubble's law E) the critical density of the universe
Answer: B
31) How do astronomers create three-dimensional maps of the universe? A) through comparison of computer models of the structure formation with observations B) by using the position on the sky and the redshift to determine a distance along the line of sight C) by using the position on the sky and the galaxy brightness as a measure of distance along the line of sight D) by interpreting the peculiar velocities of each galaxy E) by carefully measuring the parallax of each galaxy
Answer: B
32) You are feeling like spaghetti. Although normally only about 2 meters tall, you are now about 25 meters long. (How fortunate, if painful, that the being has arranged for your body to become elastic enough so that it is not ripped apart under these conditions.) As you look up over your head, you see things moving pretty quickly in the universe-but that lasts only for a brief instant, and then all contact with the universe is lost. Where are you? A) You are plunging into the Sun. B) You are crossing the event horizon of a black hole. C) You are being consumed by a "crack" in the universe caused by inflation. D) You are near the center of a star that has just developed an iron core, leading to a supernova. E) You are in a medieval torture chamber somewhere in western Europe.
Answer: B
33) You are once again in a hot, dense place. You are surrounded by protons and neutrons, some rapidly fusing into helium. You notice that your surroundings are cooling (good, because it's really hot!) and rapidly dropping in density. Within about 3 minutes, the fusion reactions stop. Where are you? A) You are in the center of a star very much like our Sun. B) You are in the early universe during the era of nucleosynthesis. C) You are inside a nuclear power plant on Earth. D) You are in the center of a star much smaller than the Sun. E) You are in the center of a massive star near the end of its life.
Answer: B
1) How do we determine the conditions that existed in the very early universe? A) We look all the way to the cosmological horizon, where we can see the actual conditions that prevailed all the way back to the first instant of the Big Bang. B) The conditions in the very early universe must have been much like those found in stars today, so we learn about them by studying stars. C) We work backward from current conditions to calculate what temperatures and densities must have been when the observable universe was much smaller in size. D) We can only guess at the conditions, since we have no way to calculate or observe what they were.
Answer: C
1) Why do we call dark matter "dark"? A) It emits no visible light. B) We cannot detect the type of radiation that it emits. C) It emits no or very little radiation of any wavelength. D) It blocks out the light of stars in a galaxy.
Answer: C
1) Why do we call dark matter "dark"? A) It is dark brown or dark red in color. B) It blocks out the light of stars in a galaxy. C) It emits no radiation that we have been able to detect. D) It contains large amounts of dark-colored dust.
Answer: C
10) If observations had shown that the cosmic microwave background was perfectly smooth (rather than having very slight variations in temperature), then we would have no way to account for A) the relationship between the strong and the weak force. B) the fact that our universe is expanding. C) how galaxies came to exist. D) the existence of helium in the universe.
Answer: C
10) When we say that a cluster of galaxies is acting as a gravitational lens, what do we mean? A) It magnifies the effects of gravity that we see in the cluster. B) It is an unusually large cluster that has a lot of gravity. C) It bends or distorts the light coming from galaxies located behind it. D) The overall shape of the cluster is that of a lens.
Answer: C
10) When we see that a spectral line of a galaxy is broadened, that is, spanning a range of wavelengths, we conclude that A) we do not have very good resolution of a star's orbital velocity. B) there are many stars traveling at extremely high orbital velocities. C) there are different Doppler shifts among the individual stars in the galaxy. D) we are actually measuring the orbital velocity of a cloud of atomic gas. E) we are actually measuring the orbital velocity of dark matter.
Answer: C
11) A large mass-to-light ratio for a galaxy indicates that A) the galaxy is very massive. B) the galaxy is not very massive. C) on average, each solar mass of matter in the galaxy emits less light than our Sun. D) on average, each solar mass of matter in the galaxy emits more light than our Sun. E) most stars in the galaxy are more massive than our Sun.
Answer: C
13) What do we mean when we say that particles such as neutrinos or WIMPs are weakly interacting? A) The light that they emit is so weak that it is undetectable to our telescopes. B) They are only weakly bound by gravity, which means they can fly off and escape from galaxies quite easily. C) They respond to the weak force but not to the electromagnetic force, which means they cannot emit light. D) They interact with other matter only through the weak force and not through gravity or any other force.
Answer: C
15) What kinds of atomic nuclei formed during the era of nucleosynthesis? A) only hydrogen B) only helium C) hydrogen and helium and trace amounts of deuterium and lithium D) roughly equal amounts of each of the following: hydrogen, helium, deuterium and lithium E) nuclei of all the chemical elements
Answer: C
15) Which of the following methods used to determine the mass of a cluster does not depend on Newton's laws of gravity? A) measuring the orbital velocities of galaxies in a cluster B) measuring the temperature of X-ray gas in the intracluster medium C) measuring the amount of distortion caused by a gravitational lens D) none of the above
Answer: C
16) Hubble's constant is related to the age of the universe, but the precise relationship depends on the way in which the expansion rate changes with time. For a given value of Hubble's constant today (such as 24 km/s/Mly), the age of the universe is oldest if what is true? A) The expansion rate has remained nearly constant with time (a coasting universe). B) The expansion rate has slowed by the amount expected for a universe with the critical density (a critical universe). C) The expansion rate has been increasing with time (an accelerating universe). D) The expansion rate is slowing dramatically with time (a recollapsing universe).
Answer: C
16) The Big Bang theory seems to explain how elements were formed during the first few minutes after the Big Bang. Which hypothetical observation below (these are not real observations) would call our current theory into question? A) the discovery of a star-like object made entirely of carbon and oxygen B) the discovery of a planet that with no helium in its atmosphere C) the discovery of a galaxy with a helium abundance of only 10% by mass D) the discovery of a galaxy with 27% helium rather than the 25% that theory tells us was produced in the Big Bang
Answer: C
16) Why is the era of nucleosynthesis so important in determining the chemical composition of the universe? A) All the elements except hydrogen were produced after the era of nucleosynthesis. B) We can observe spectra from this era to determine what the primordial mix of the elements was at the beginning of the universe. C) 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. D) We can study the processes that occurred during the era of nucleosynthesis to determine how most of the elements in the universe were created. E) By knowing how much matter was created during the era of nucleosynthesis, we can determine whether the universe is open or closed.
Answer: C
17) Imagine that it turns out that dark matter (not dark energy) is made up of an unstable form of matter that decays into photons or other forms of energy about 50 billion years from now. Based on current understanding, how would that affect the universe at that time? A) Stars would cease to exist when the dark matter is gone. B) Planetary systems would expand and disperse. C) The galaxies in clusters would begin to fly apart. D) The universe would cease its expansion.
Answer: C
17) Which of the following statements about rich clusters of galaxies (those with thousands of galaxies) is not true? A) They are sources of X-ray emission due to the presence of hot, intergalactic gas. B) There likely have been numerous collisions among the member galaxies at some time in the past. C) Galaxies in the central regions are predominantly spirals, while elliptical galaxies roam the outskirts. D) They often have a very large, central dominant galaxy near their center, perhaps formed by the merger of several individual galaxies. E) The speeds of the galaxies in the cluster indicate that most of the cluster mass is dark matter.
Answer: C
39) What is the evidence for an accelerating universe? A) White-dwarf supernovae are the same brightness regardless of redshift. B) White-dwarf supernovae are slightly brighter than expected for a coasting universe. C) White-dwarf supernovae are slightly dimmer than expected for a coasting universe. D) The Andromeda Galaxy is moving away from the Milky Way at an ever-increasing speed. E) There is far more dark matter than visible matter in the universe.
Answer: C
4) The flat rotation curves of spiral galaxies tell us that they contain a lot of dark matter. Do they tell us anything about where the dark matter is located within the galaxy? A) Yes, they tell us that dark matter is concentrated near the center of the galaxy. B) Yes, they tell us that dark matter is spread uniformly throughout the galactic disk. C) Yes, they tell us that dark matter is spread throughout the galaxy, with most located at large distances from the galactic center. D) No, we cannot determine anything about the location of dark matter from the rotation curve.
Answer: C
6) What do we mean by inflation? A) the expansion of the universe that we still observe today B) the sudden release of photons when a particle and antiparticle annihilate one another C) a sudden and extremely rapid expansion of the universe that occurred in a tiny fraction of a second during the universe's first second of existence D) quantum fluctuations by high speed, relativistic particles in a state of false vacuum that caused disturbances in the space-time continuum leading to the process described in the question to which this answer refers
Answer: C
6) When we say that the electromagnetic and weak forces "freeze out" from the electroweak force at 10-10 seconds after the Big Bang, we mean that A) these forces are important only at temperatures below the freezing point of water-a temperature that the universe reached at an age of about 10-10 second. B) "freezing out" was a term coined by particle physicists who think that the Big Bang theory is really cool. C) prior to this time the electromagnetic and weak forces maintained a single identity, but they possessed separate identities following this time. D) following this time neither the electromagnetic nor the weak force was ever important in the universe again. E) 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.
Answer: C
8) How does gravitational lensing tell us about the mass of a galaxy cluster? A) The lensing allows us to determine the orbital speeds of galaxies in the cluster, so that we can determine the mass of the cluster from the orbital velocity law. B) The lensing broadens spectral lines, and we can use the broadening to "weigh" the cluster. C) Using Einstein's general theory of relativity, we can calculate the cluster's mass from the precise way in which it distorts the light of galaxies behind it. D) Newton's universal law of gravitation predicts how mass can distort light, so we can apply Newton's law to determine the mass of the cluster.
Answer: C
8) Which statement about the cosmic microwave background is not true? A) Its spectrum corresponds to a temperature of just under 3 degrees above absolute zero. B) With the exception of very small variations, it appears essentially the same in all directions in which we look into space. C) It is the result of a mixture of radiation from many independent sources, such as stars and galaxies. D) It is thought to be radiation that began its journey to our telescopes when the universe was about 380,000 years old.
Answer: C
10) Is space expanding within clusters of galaxies? A) No, because the universe is not old enough yet for these objects to have begun their expansion. B) No, because expansion of the universe affects only empty space, not space in which matter is present. C) Yes, and that is why clusters tend to grow in size with time. D) No, because their gravity is strong enough to hold them together even while the universe as a whole expands.
Answer: D
11) Which of the following statements about large-scale structure is probably not true? A) Galaxies and clusters have grown around tiny density enhancements that were present in the early universe. B) Voids between superclusters began their existence as regions in the universe with a slightly lower density than the rest of the universe. C) Many cluster and superclusters are still in the process of formation as their gravity gradually pulls in new members. D) Clusters and superclusters appear to be randomly scattered about the universe, like dots sprinkled randomly on a wall.
Answer: D
12) How does the idea of inflation account for the existence of the "seeds" of density from which galaxies and other large structures formed? A) Inflation predicts that gravity would have been very strong and thereby would have concentrated mass into seeds. B) Inflation tells us that the universe should have a "flat" overall geometry, and this led to the flat disks of galaxies. C) Inflation predicts that temperatures and densities should have become nearly equal throughout the universe. D) Inflation would have caused random, microscopic quantum fluctuations to grow so large in size that they became the seeds of structure.
Answer: D
12) What direct evidence do we have that the weak and electromagnetic forces were once unified as a single electroweak force? A) The most advanced telescopes are able to see back to this era in the universe. B) Detectors on Earth have received photons and high-energy particles from this era. C) Temperatures in the center of the Sun can reproduce the conditions during this era. D) Particle accelerators on Earth can reach energies equivalent to the high temperatures of this era and have produced particles predicted by the electroweak theory. E) We have no direct evidence of the electroweak force.
Answer: D
12) What is the distinguishing characteristic of what we call ordinary or baryonic matter? A) It emits a great deal of light. B) It can attract other matter through the force of gravity. C) It is made of subatomic particles that scientists call WIMPs. D) It consists of atoms or ions with nuclei made from protons and neutrons.
Answer: D
12) What is the mass-to-light ratio for the inner region of the Milky Way Galaxy, in units of solar masses per solar luminosity? A) 1,000 B) 600 C) 100 D) 6 E) 0.1
Answer: D
13) Which of the following is not consistent with recent observations of the cosmic microwave background by the WMAP satellite? A) The universe is geometrically "flat" (in the four dimensions of spacetime). B) The matter density (both luminous and dark matter combined) in the universe is only about one-fourth of the critical density. C) Dark energy, whatever it is, represents the majority of the energy content of the universe. D) The universe is at least 20 billion years old.
Answer: D
14) Approximately how long did the era of nucleosynthesis last? A) 10-10 second B) 0.001 second C) 5 seconds D) 5 minutes E) 5 years
Answer: D
14) Based on the results from the WMAP satellite, the overall composition of the universe is A) 100% ordinary (baryonic) matter. B) 15% ordinary (baryonic) matter, 85% nonbaryonic dark matter. C) 1% ordinary (baryonic) matter, 99% nonbaryonic dark matter. D) 4% ordinary (baryonic) matter, 23% nonbaryonic dark matter, 73% dark energy.
Answer: D
14) Olbers's paradox is an apparently simple question, but its resolution suggests that the universe is finite in age. What is the question? A) What would it be like to ride on a beam of light? B) How many stars are in the universe? C) Can we measure the position and momentum of an electron at the same time? D) Why is the sky dark at night?
Answer: D
15) When we speak of the large-scale structure of the universe, we mean A) the structure of any large galaxy. B) the structure of any individual cluster of galaxies. C) the overall shape of the observable universe. D) the overall arrangement of galaxies, clusters of galaxies, and superclusters in the universe.
Answer: D
16) Why wasn't the intracluster medium in galaxy clusters discovered until the 1960s? A) We did not know how much dark matter existed before then. B) We didn't have the resolution to observe galaxy clusters until then. C) The Milky Way was blocking our view of distant galaxy clusters. D) The medium emits X rays, which are blocked by the Earth's atmosphere and require X-ray satellites in space in order to be observed. E) Radiation emitted by the medium was so dim that we couldn't detect it until we built much larger telescopes.
Answer: D
17) What is the primary form of evidence that has led astronomers to conclude that the expansion of the universe is accelerating? A) observations of the speeds of individual galaxies in clusters B) measurements of the rotation curve for the universe C) measurements of how galaxy speeds away from the Milky Way have increased during the past century D) observations of white dwarf supernovae
Answer: D
20) Where do the photons in the cosmic background radiation originate? A) the moment of the Big Bang B) the end of the Planck era C) during the era of nucleosynthesis D) the end of the era of nuclei E) during the era of galaxy formation
Answer: D
23) Based on current evidence concerning the amount of deuterium in the universe, we can conclude that A) ordinary (baryonic) matter makes up most of the mass of the universe. B) neutrons greatly outnumber protons in the universe. C) most of the deuterium that was created during the era of nucleosynthesis has since been destroyed. D) the density of ordinary (baryonic) matter is between 1 percent and 10 percent of the critical density. E) we live in a critical-density universe.
Answer: D
23) Helium originates from A) stellar nucleosynthesis only. B) the Big Bang only. C) stellar nucleosynthesis with a small contribution from the Big Bang. D) the Big Bang with a small contribution from stellar nucleosynthesis. E) radioactive decay of heavier elements only.
Answer: D
25) Why can't the dark matter in galaxies be made of neutrinos? A) There are not enough neutrinos to make up all the dark matter. B) Neutrinos do not have any mass they interact only through the weak force. C) We know that dark massive objects such as planets and neutron stars are not made of neutrinos. D) Neutrinos travel at extremely high speeds and can escape a galaxy's gravitational pull. E) Big Bang nucleosynthesis constrains how many neutrinos there are in the Universe.
Answer: D
27) Olbers' paradox is an apparently simple question, but its resolution suggests that the universe is finite in age. What is the question? A) What would it be like to ride on a beam of light? B) Can we measure the position and momentum of an electron at the same time? C) How does the Sun produce energy? D) Why is the sky dark at night? E) How many stars are in the universe?
Answer: D
28) Why isn't space expanding within systems such as our solar system or the Milky Way? A) Hubble's law of expansion applies only to the space between galaxies. B) We are so close to these systems that we don't observe their expansion. C) The universe is not old enough yet for these objects to begin their expansion. D) Their gravity is strong enough to hold them together against the expansion of the universe.
Answer: D
29) You are in a place that is extremely hot and dense, making you feel quite sweaty and claustrophobic. You can't see far because your surroundings are opaque to light. Around you, nuclear fusion is converting carbon into oxygen and other elements. Where are you? A) You are in the center of a star very much like our Sun. B) You are in the early universe during the era of nucleosynthesis. C) You are inside a nuclear power plant on Earth. D) You are in the center of a massive star near the end of its life. E) You are in the center of a star much smaller than the Sun.
Answer: D
32) What does the universe look like on very large scales? A) Galaxies are uniformly distributed. B) Galaxies are randomly distributed. C) Galaxies are distributed in a hierarchy of clusters, superclusters, and hyperclusters. D) Galaxies appear to be distributed in chains and sheets that surround great voids. E) Galaxies are distributed in a great shell expanding outward from the center of the universe.
Answer: D
34) At last you are in a place where the heat and high density are no longer bothering you. However, although the density is very low, the gas around you is extremely high in temperature. In fact, the temperature is so high that it is emitting lots of X rays, which are creating cancer-causing mutations in your body at a rapid rate. Well, at least the view is great! There are no stars anywhere within about 10,000 light-years of you, but at slightly greater distances your sky is brightened by many beautiful, star-filled structures, some with majestic spiral shapes. Where are you? A) You are in the universe when it was about 200 million years old, just before galaxies began forming. B) You are in the center of the Milky Way Galaxy, looking outward into the Local Group. C) You are somewhere between the Andromeda and Milky Way galaxies in the Local Group. D) You are in intergalactic space within a rich cluster of thousands of galaxies. E) You are in the outskirts of a galaxy whose nucleus is a powerful quasar.
Answer: D
6) If there is no dark matter in the Milky Way Galaxy, what is the best alternative explanation for the observations? A) We are not measuring the orbital velocities of atomic clouds and stars properly. B) We are not measuring the distances to atomic clouds and stars properly. C) We are not attributing enough mass to the visible or "bright" matter. D) We are not observing all the visible or "bright" matter in the galaxy. E) Our understanding of gravity is not correct for galaxy-size scales.
Answer: E
8) 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? A) gravity and the weak force B) gravity and the strong force C) the strong and weak forces D) the strong and electromagnetic forces E) the electromagnetic and weak forces
Answer: E
1) To date, physicists have investigated the behavior of matter and energy at temperatures as high as those that existed in the universe as far back as ________ after the Big Bang. A) 1 million years B) 300,000 years C) 300 years D) 3 minutes E) 10-10 second
E
1) Which of the following best summarizes what we mean by dark matter? A) matter that we have identified from its gravitational effects but that we cannot see in any wavelength of light B) matter that may inhabit dark areas of the cosmos where we see nothing at all C) matter consisting of black holes D) matter for which we have theoretical reason to think it exists, but no observational evidence for its existence
Answer: A
10) (From a science quiz that appeared in the weekly magazine The Economist.) Economic history is easier to write than the history of the universe. Nevertheless, most cosmologists now think that when the universe was formed, A) first there was a Big Bang, then inflation (of space) caused recession (of all matter, away from the Big Bang). B) first there was inflation, which caused the Big Bang, then recession. C) first there was a Big Bang. There has not been any inflation yet, but if it comes it will cause recession.
Answer: A
11) In stars, helium can sometimes be fused into carbon and heavier elements (in their final stages of life). Why didn't the same fusion processes produce carbon and heavier elements in the early universe? A) By the time stable helium nuclei had formed, the temperature and density had already dropped too low for helium fusion to occur. B) Helium fusion occurred, but the carbon nuclei that were made were later destroyed by the intense radiation in the early universe. C) Temperatures in the early universe were never above the roughly 100 million Kelvin required for helium fusion. D) No one knows—this is one of the major mysteries in astronomy.
Answer: A
11) The idea of dark matter arose to explain gravitational effects observed in galaxies and clusters of galaxies. However, studies of the early universe (especially of the cosmic microwave background and of chemical abundances) also tell us something about dark matter. What do they tell us? A) They add further support to the idea that dark matter really exists and is made of non-ordinary (nonbaryonic) matter, such as WIMPs. B) They do not support the conclusion that dark matter is the dominant form of matter in the universe. C) They tell us that dark matter probably exists, but that it must be made of ordinary (baryonic) matter in the form of MACHOs. D) They tell us that dark matter was produced during the era of nuclei.
Answer: A
29) What are peculiar velocities? A) velocities perpendicular to our line of sight B) velocities directly along our line of sight C) velocities that we cannot explain by only the force of gravity D) velocities caused by the expansion of the universe E) velocities of distant objects that are not caused by the expansion of the universe
Answer: E
3) Why do we believe 90 percent of the mass of the Milky Way is in the form of dark matter? A) The orbital speeds of stars far from the galactic center are surprisingly high, suggesting that these stars are feeling gravitational effects from unseen matter in the halo. B) Although dark matter emits no visible light, it can be seen with radio wavelengths, and such observations confirm that the halo is full of this material. C) Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least 10 times as much matter as we see in the Milky Way disk, suggesting that the halo is full of dark matter. D) Our view of distant galaxies is sometimes obscured by dark blotches in the sky, and we believe these blotches are dark matter located in the halo.
Answer: A
31) It sure is bright everywhere you've been able to travel around a bit, and it's clear that you are not in a star. Yet it is as bright as looking directly at the Sun. In your extensive travels through your current surroundings, you cannot find a single neutral atom anywhere, nor can you find a nucleus besides hydrogen or helium. And, while it is hot (a few thousand degrees Kelvin), it is nowhere near the temperature needed for nuclear fusion. Where are you? A) You are in the universe during its first 300,000 years. B) You are in the universe more than 10100 years in the future. C) You are in an accretion disk around a supermassive black hole. D) You are in the central regions of a quasar. E) You are where the Sun should be located, but about 5 billion years from now.
Answer: A
33) What fraction of the mass needed to halt expansion is known to exist in the form of visible mass in the universe? A) 1 percent B) 4 percent C) 22 percent D) 74 percent E) 100 percent
Answer: A
35) If all the "dark matter" in the Universe were to be, somehow, instantaneously removed, which of the following would not happen? A) The Solar System would fly apart. B) The Milky Way would fly apart. C) Clusters of galaxies would fly apart. D) The Universe would expand forever. E) all of the above
Answer: A
36) Which model of the universe gives the youngest age for its present size? A) a recollapsing universe B) a coasting universe C) a critical universe D) an accelerating universe E) all models give the same age
Answer: A
4) The four fundamental forces that operate in the universe today are A) strong force, weak force, electromagnetic force, gravity. B) strong force, weak force, electric force, magnetic force. C) nuclear force, electromagnetic force, gravity, tidal force. D) nuclear force, gravity, electric force, magnetic force.
Answer: A
4) Why can't current theories describe what happened during the Planck era? A) We do not yet have a theory that links quantum mechanics and general relativity. B) We do not understand the properties of antimatter. C) We do not know how much energy existed during that time. D) It was a time period from which we cannot receive radiation. E) The Planck era was the time before the Big Bang, and we cannot describe what happened before that instant.
Answer: A
42) What is not a main source of evidence for the existence of dark matter? A) massive blue stars B) rotation curves of disk galaxies C) stellar motions in elliptical galaxies D) velocities and positions of galaxies in clusters of galaxies E) gravitational lensing by clusters of galaxies
Answer: A
5) It is more difficult to determine the total amount of dark matter in an elliptical galaxy than in a spiral galaxy. Why? A) Elliptical galaxies lack the atomic hydrogen gas that we use to determine orbital speeds at great distances from the centers of spiral galaxies. B) Elliptical galaxies contain much less dark matter than spiral galaxies, so it's much more difficult to measure. C) Stars in elliptical galaxies are dimmer, making them harder to study. D) We cannot observe spectral lines for elliptical galaxies.
Answer: A
5) Laboratory experiments conducted with particle accelerators confirm predictions made by the theory that unifies A) the electromagnetic and weak forces into the electroweak force. B) the strong, weak, and electromagnetic forces into the GUT force. C) the unification of all four forces into a single "superforce." D) the strong and weak forces into the combined nuclear force.
Answer: A
5) What evidence suggests that the Milky Way contains dark matter? A) We observe clouds of atomic hydrogen far from the galactic center orbiting the galaxy at unexpectedly high speeds, higher speeds than they would have if they felt only the gravitational attraction from objects that we can see. B) We see many lanes of dark material blocking out the light of stars behind them along the band of the Milky Way. C) We see many dark voids between the stars in the halo of the Milky Way. D) When we observe in different wavelengths, such as infrared or radio, we see objects that don't appear in visible-light observations. E) When we look at the galactic center, we are able to observe a large black hole that is composed of dark matter.
Answer: A
7) According to the Big Bang theory, why do we live in a universe that is made of almost entirely of matter rather than antimatter? A) During the first 0.001 second after the Big Bang, particles and antiparticles were made in almost but not perfectly equal numbers. Everything annihilated except the very slight excess of matter particles. B) GUT theories predict that under the conditions that prevailed in the early universe, the normal laws of physics would have been suspended so that only matter particles were created, and no particles of antimatter. C) The fact that we live in a universe made of matter is not surprising, because antimatter has never been shown to exist for real. D) Einstein's famous equation E = mc2 tells us that energy can turn into matter, but does not tell us that it can turn into antimatter.
Answer: A
7) Although we know less about dark matter in elliptical galaxies than in spiral galaxies, what does current evidence suggest? A) Elliptical galaxies probably contain about the same proportion of their mass in the form of dark matter as do spiral galaxies. B) Elliptical galaxies probably contain far less dark matter than spiral galaxies. C) Elliptical galaxies probably contain far more dark matter than spiral galaxies. D) Unlike the broad distribution of dark matter in spiral galaxies, elliptical galaxies probably contain dark matter only near their centers.
Answer: A
40) What might be causing the universe to accelerate? A) WIMPs B) neutrinos C) white-dwarf supernovae D) dark gravity E) We don't know!-but we call it "dark energy."
Answer: E
7) Which of the following statements correctly summarizes the events in the early universe according to the Big Bang theory? A) The universe began with the forces unified. During the first fraction of a second, the forces separated and there was a brief but important episode of inflation. Subatomic particles of both matter and antimatter then began to appear from the energy present in the universe. Most of the particles annihilated to make photons, but some became protons, neutrons, electrons, and neutrinos. The protons and neutrons underwent some fusion during the first three minutes, thereby determining the basic chemical composition of the universe. B) An episode of what we call inflation initiated the event of the Big Bang. Once the Big Bang got underway, particles and forces began to appear one by one. The forces produced protons, which fused to make hydrogen and helium until the universe was about 380,000 years old. Then gravity began to act, turning the hydrogen and helium into galaxies. C) Forces and various subatomic particles began to appear during the first second after the Big Bang. For reasons not understood, the particles were all made of ordinary matter and none were made of antimatter, thus explaining why we live in a universe made of matter. The particles underwent some fusion for the first 380,000 years after the Big Bang, at which time the first stars were born. D) The Big Bang began with the initiation of what we call inflation, which gradually slowed to the current expansion rate of the universe. Forces came to exist for a different reason, having to do with quantum fluctuations in the space-time continuum. Particles came to exist as a result of cracks made when forces froze. Once there were particles, gravity brought them together to make stars, and the stars then turned the particles into hydrogen, helium, and other elements.
Answer: A
9) If WIMPs really exist and make up most of the dark matter in galaxies, which of the following is not one of their characteristics? A) They travel at speeds close to the speed of light. B) They are subatomic particles. C) They can neither emit nor absorb light. D) They tend to orbit at large distances from the galactic center.
Answer: A
1) Based on our current understanding of physics, we can understand the conditions that prevailed in the early universe as far back in time as about A) 380,000 years after the Big Bang. B) one ten-billionth of a second after the Big Bang. C) 10-45 seconds after the Big Bang. D) 10 billion years ago.
Answer: B
10) Measuring the amount of deuterium in the universe allows us to set a limit on A) the total amount of mass in the universe. B) the density of ordinary (baryonic) matter in the universe. C) the acceleration of the universe. D) the current age of the universe.
Answer: B
13) Based on current evidence, how does the actual average density of matter in the universe compare to the critical density? A) If we include dark matter, the actual density equals the critical density. B) The actual density, even with dark matter included, is less than about a third of the critical density. C) The actual density of dark matter and luminous matter combined is no more than about 1% of the critical density. D) The actual density of matter is many times higher than the critical density.
Answer: B
13) The idea of inflation makes one clear prediction that, until the discovery of an accelerating expansion, seemed to contradict the available observations. What is this prediction? A) Inflation predicts that the early universe should have regions of enhanced density that could have acted as "seeds" for the formation of galaxies and large structures. B) The universe should be geometrically "flat" (in the four dimensions of spacetime). C) Inflation predicts that the temperature of the cosmic microwave background should be almost (but not exactly) the same everywhere. D) Inflation predicts that the entire universe must be far larger than the observable universe.
Answer: B
14) If a galaxy's overall mass-to-light ratio is 100 solar masses per solar luminosity, and its stars account for only 5 solar masses per solar luminosity, how much of the galaxy's mass must be dark matter? A) 100 percent B) 95 percent C) 80 percent D) 50 percent E) 5 percent
Answer: B
14) Which of the following statements best describes the current state of understanding regarding the apparent acceleration of the expansion of the universe? A) The cause of the acceleration is well-understood, and attributed to the particles that make up dark energy. B) We have moderately strong evidence that the acceleration is real, but essentially no idea what is causing it. C) The acceleration is very important in the cosmos today, but the evidence indicates that it will eventually slow down, allowing the universe to recollapse. D) The acceleration probably is not real, and what we attribute to acceleration is probably just a misinterpretation of the data.
Answer: B
15) Some people wish that we lived in a recollapsing universe that would eventually stop expanding and start contracting. For this to be the case, which of the following would have to be true (based on current understanding)? A) Dark energy is the dominant form of energy in the cosmos. B) Dark energy does not exist and there is much more dark matter than we are aware of to date. C) Neither dark energy nor dark matter really exist. D) Dark energy exists but dark matter does not.
Answer: B
15) Which adjective does not necessarily describe a known feature of the early universe? (Be sure to consider the universe as a whole, not just the observable universe.) A) dense B) small C) hot D) filled with intense radiation
Answer: B
16) Which of the following statements cannot be tested by science today? A) Our universe is flat. B) Prior to the Planck time, our universe sprouted from another universe. C) The universe is 14 billion years old. D) The expansion of the universe is now accelerating.
Answer: B
17) Why did the era of nuclei end when the universe was about 300,000 years old? A) All the free particles had combined to form the nuclei of atoms. B) The universe had expanded and cooled to a temperature of about 3,000 K, cool enough for stable, neutral atoms to form. C) Neutrinos and electrons were finally able to escape the plasma of the early universe and no longer heated the other particles. D) Photons were finally able to escape the plasma of the early universe and no longer heated the hydrogen and helium ions. E) No theory can explain this.
Answer: B
19) Which of the following statements about the cosmic background radiation is not true? A) It has a temperature of about 3 degrees K above absolute zero. B) It is the result of a mixture of radiation from many independent sources, such as stars and galaxies. C) It had a much higher temperature in the past. D) It was discovered by Penzias and Wilson in the early 1960s. E) It appears essentially the same in all directions (it is isotropic).
Answer: B
4) How do we know that there is much more mass in the halo of our galaxy than in the disk? A) There are so many globular clusters in the halo that their total mass is greater than the mass of stars in the disk. B) Stars in the outskirts of the Milky Way orbit the galaxy at much higher speeds than we would expect if all the mass were concentrated in the disk. C) Although the question of mass in the halo was long mysterious, we now know it exists because we see so many brown dwarfs in the halo. D) The recent discovery of photinos, combined with theoretical predictions, tells us that there must be a huge mass of photinos in the halo. E) We don't know that there is more mass in the halo it is only a guess based on theory.
Answer: B
4) What is a rotation curve? A) a precise description of the shape of a star's orbit around the center of the Milky Way Galaxy B) a graph showing how orbital velocity depends on distance from the center for a spiral galaxy C) a curve used to decide whether a star's orbit places it in the disk or the halo of a spiral galaxy D) a graph that shows a galaxy's mass on the vertical axis and size on the horizontal axis
Answer: B
6) What do we mean when we say that the rotation curve for a spiral galaxy is "flat"? A) The amount of light emitted by stars at different distances is about the same throughout the galaxy. B) Gas clouds orbiting far from the galactic center have approximately the same orbital speed as gas clouds located further inward. C) The disk of a spiral galaxy is quite flat rather than spherical like the halo. D) All the galaxy's mass is concentrated in its flat, gaseous disk.
Answer: B
6) What was the significance of the end of the era of nucleosynthesis, when the universe was about 5 minutes old? A) The proportions of dark matter and luminous matter had been determined. B) The basic chemical composition of the universe had been determined. C) It marks the time at which the first stars formed. D) It marks the time at which the expansion of the universe had settled down to its current rate.
Answer: B
7) How are rotation curves of spiral galaxies determined beyond radii where starlight can be detected? A) by extrapolation B) through observations of the 21 cm line of atomic hydrogen C) through observations of spectral lines of dark matter D) by watching the galaxies rotate over a period of years E) by measuring the broadening of absorption lines
Answer: B
7) How many forces operated in the universe during the GUT era? A) one, what we call the "super force" B) two, gravity and the GUT force C) two, gravity and the electroweak force D) three, gravity, the strong force, and the electroweak force E) all of the above forces
Answer: B
7) Why does the temperature of the gas between galaxies in galaxy clusters tell us about the mass of the cluster? A) The temperature is always directly related to mass, which is why massive objects are always hotter than less massive objects. B) The temperature tells us the average speeds of the gas particles, which are held in the cluster by gravity, so we can use these speeds to determine the cluster mass. C) The temperature of the gas tells us the gas density, so we can use the density to determine the cluster's mass. D) The question is nonsense—gas temperature cannot possibly tell us anything about mass.
Answer: B
8) In general, when we compare the mass of a galaxy or cluster of galaxies to the amount of light it emits (that is, when we look at it mass-to-light ratio), we expect that A) the higher amount of mass relative to light (higher mass-to-light ratio), the lower the proportion of dark matter. B) the higher the amount of mass relative to light (higher mass-to-light ratio), the greater the proportion of dark matter. C) the amount of light should be at least one solar luminosity for each solar mass of matter (mass-to-light ratio less than or equal to 1). D) the higher the amount of mass relative to light (higher mass-to-light ratio), the older the galaxy or cluster.
Answer: B
8) The distribution of the dark matter in a spiral galaxy is A) approximately spherical and about the same size as the galaxy halo. B) approximately spherical and about ten times the size of the galaxy halo. C) flattened in a disk and about the same size as the stellar disk. D) flattened in a disk but about ten times larger than the stellar disk. E) predominantly concentrated in the spiral arms.
Answer: B
9) How do we determine the amount of dark matter in elliptical galaxies? A) We measure the orbital velocities of star-forming gas clouds around the outer portions of the galaxy. B) We measure the speeds of stars at different radii from the galactic center and determine how much mass is interior to the orbit. C) We count the number of stars in the galaxy and determine its volume, so that we can calculate the galaxy's density. D) We search for dark lanes of dust and black holes within the galaxy. E) We measure how fast the galaxy rotates as a whole.
Answer: B
9) In principle, if we could see all the way to the cosmological horizon we could see the Big Bang taking place. However, our view is blocked for times prior to about 380,000 years after the Big Bang. Why? A) Before that time, the universe was too crowded with stars. B) Before that time, the gas in the universe was dense and ionized and therefore did not allow light to travel freely. C) Before that time, the universe was dark so there was no light to illuminate anything. D) 380,000 years after the Big Bang marks the time when stars were first born, and thus began to shine the light by which we can see the universe.
Answer: B
9) What do we mean by inflation? A) what happened the instant after the Big Bang B) a sudden expansion of the universe after the strong force froze out from the GUT force C) the expansion of the universe that we still observe today D) the sudden release of photons when a particle and antiparticle annihilate each other E) the separation that occurs after two photons collide and create a particle and an antiparticle
Answer: B
Refer to this scenario for the following questions: 28) You find yourself in a place that looks (except for your own presence) perfectly symmetrical. There is no way to distinguish one place from another, and all forces are one. With this perfect symmetry, there is no obvious way to define the flow of time. Where are you? A) You are in the center of a young star. B) You are in the early universe before the Planck time. C) You are floating somewhere in the universe near its end, 10100 years from now. D) You are inside the nucleus of an atom. E) You are in the universe shortly after inflation.
Answer: B
18) 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? A) 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). B) The cosmic background radiation is expected to have a perfect thermal spectrum, and observations from the COBE spacecraft verify this prediction. C) The cosmic background radiation is expected to contain spectral lines of hydrogen and helium, and it does. D) The cosmic background radiation is expected to look essentially the same in all directions, and it does. E) 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.
Answer: C
18) Which of the following best sums up current scientific thinking about the nature of dark energy? A) Dark energy most likely consists of a form of photons that we can't see or detect. B) Dark energy is most likely made up of weakly interacting particles that do not interact with light. C) Dark energy probably exists, but we have little (if any) idea what it is. D) Dark energy is the source of the mind weapon used by Sith Lords in Star Wars.
Answer: C
2) What is meant by "dark energy"? A) the energy associated with dark matter through E=mc2 B) any unknown force that opposes gravity C) the agent causing the universal expansion to accelerate D) highly energetic particles that are believed to constitute dark matter E) the total energy in the Universe after the Big Bang but before the first stars
Answer: C
2) Why can't current theories describe what happened during the Planck era? A) We do not know how hot or dense the universe was during that time. B) We do not understand the properties of antimatter. C) We do not yet have a theory that links quantum mechanics and general relativity. D) The Planck era was the time before the Big Bang, and we cannot describe what happened before that instant.
Answer: C
20) Which of the following particles are baryons? A) electrons B) neutrinos C) protons D) quarks E) photons
Answer: C
22) Measuring the amount of deuterium in the universe allows us to set a limit on A) the temperature of the universe at the end of the era of nuclei. B) the total amount of mass in the universe. C) the density of ordinary (baryonic) matter in the universe. D) the expansion rate of the universe. E) the current age of the universe.
Answer: C
26) What is postulated to have caused a sudden inflation of the early universe? A) the annihilation of matter and antimatter B) the separation of the electromagnetic and weak forces C) the "freezing out" of the strong force from the GUT force D) the energy released in the fusion of protons and neutrons to produce helium E) giant quantum fluctuations
Answer: C
27) Why do we expect WIMPs to be distributed throughout galactic halos, rather than settled into a disk? A) They are light enough that they have expanded out into the halo. B) WIMPs were produced at the early stages of galaxy evolution, and objects in the halo, such as globular clusters, were formed at the beginning of the galaxy. C) Since they do not interact with the electromagnetic force, they do not feel friction or drag and hence do not contract with the rest of the protogalactic cloud. D) Shock waves from supernovae have blown the WIMPs out into the halo. E) Jets from the early active stage of a galaxy's life shot out most of the WIMPs from the disk.
Answer: C
3) The text states that luminous matter in the Milky Way seems to be much like the tip of an iceberg. This refers to the idea that A) luminous matter emits white light, much like the light reflected from icebergs. B) black holes are much more interesting than ordinary stars that give off light. C) dark matter represents much more mass and extends much further from the galactic center than the visible stars of the Milky Way. D) the luminous matter of the Milky Way is essentially floating on the surface of a great sea of dark matter.
Answer: C
30) You are on the surface of an object, and you have a fairly clear view out into space. It might be very nice, except for one major drawback: You are very squashed. Also, light you observe from distant objects is apparently slightly blueshifted (compared to what it normally looks like). The surface of the object is composed primarily of carbon and oxygen, and the horizon distance is about the same as that on Earth. By observing the stellar background for a few weeks, you realize that there are several planets orbiting your object. Where are you? A) You are on the surface of Earth. B) You are on the surface of a planet that is somewhat more massive than Earth. C) You are on the surface of a white dwarf. D) You are "on" an accretion disk around a black hole. E) You are on the surface of a neutron star.
Answer: C
34) Based on inventoried matter in the universe, including dark matter known to exist in galaxies and clusters, the actual density of the universe is what fraction of the critical density? A) 1 percent B) 10 percent C) 26 percent D) 74 percent E) 100 percent
Answer: C
37) What is the ultimate fate of an open universe? A) the Big Crunch B) Stars will expand away from each other and galaxies effectively "evaporate." C) All matter decays to a low-density sea of photons and subatomic particles. D) All matter eventually ends up in massive black holes. E) Individual stars die but their gas is recycled through the interstellar medium and new stars form in a never-ending process.
Answer: C
38) Recent measurements of the expansion rate of the universe reveal that the expansion rate of the universe is doing something astronomers did not expect. What is that? A) The measurements show that the universe may not be expanding at all. B) The measurements show that the universe may be shrinking rather than expanding. C) The measurements show that the expansion is accelerating, rather than slowing under the influence of gravity. D) The measurements indicate that the universe is at least 30 billion years old, meaning that more than 10 billion years passed between the Big Bang and the formation of the first stars and galaxies. E) The data show that the expansion rate varies widely in different parts of the universe.
Answer: C
41) What is Einstein's cosmological constant? A) the value of the expansion rate of the universe B) the value of the acceleration of the universe C) the value that measures the strength of gravity across the universe D) the size of the cosmological horizon E) a repulsive force that counteracts gravity and was introduced to allow for a static universe
Answer: E
35) At last, someplace fairly comfortable. Very weak gravity is holding you to the surface of the small object on which you sit. Your object is apparently moving away from a star, perhaps one that it orbits with a period of thousands of years. Around you, geysers are spouting gas into space. Looking back along the object's orbit, you see particles of dust that the geysers apparently blew off the object when it was nearer to the star that it is now leaving behind. You conclude that the geysers were recently much more active but are now settling down into a quiescent state that may last for millennia. You also soon realize that you are closer to home than you have been in all your previous journeys. Perhaps if you can somehow find a small rocket, a heat shield, and a good parachute, you can escape and head home for your final exam. Where are you? A) You are on an asteroid near the center of a galaxy, heading in toward a massive black hole. B) You have been shrunk in size and are riding a grain of interstellar dust that is carrying you on an orbit about our very own Sun. C) You are riding a jet of gas from a quasar that is headed in the direction of an ordinary star. D) You are on comet Hale-Bopp, circa May 1997. E) You are at Disneyland on the Moon, riding the new "wild and wet" roller coaster.
Answer: D
36) Which of the following observations is not a piece of evidence supporting the Big Bang theory? A) Darkness of the night sky B) Recession speeds of far away galaxies relative to close ones C) Observed helium abundance in the universe D) Relative motions of galaxies in the Local Group
Answer: D
4) According to the Big Bang theory, how many forces—and which ones—operated in the universe during the GUT era? A) 1 force that represented the unification of all four forces that operate today B) 3 forces: gravity, the strong force, and the electroweak force C) 2 forces: the strong force and the electroweak force D) 2 forces: gravity and a single force that later became the strong, weak, and electromagnetic forces
Answer: D
5) A "GUT" (grand unified theory) refers to theories that A) unify gravity with the strong and weak forces. B) unify the electromagnetic and weak forces. C) unify all four forces together. D) unify the strong force with the electromagnetic and weak forces.
Answer: D
5) A GUT (grand unified theory) refers to theories that A) unify all four forces. B) unify gravity and the electromagnetic and weak forces. C) unify gravity and the strong and weak forces. D) unify the strong force and the electromagnetic and weak forces. E) unify the electromagnetic and weak forces.
Answer: D
5) What is the primary way in which we determine the mass distribution of a spiral galaxy? A) We calculate its mass-to-light ratio. B) We apply Newton's version of Kepler's third law to the orbits of globular clusters in the galaxy's halo. C) We count the number of stars we can see at different distances from the galaxy's center. D) We construct its rotation curve by measuring Doppler shifts from gas clouds at different distances from the galaxy's center.
Answer: D
6) How do we know that galaxy clusters contain a lot of mass in the form of hot gas that fills spaces between individual galaxies? A) We infer its existence by observing its gravitational effects on the galaxy motions. B) The hot gas shows up as bright pink in visible-light photos of galaxy clusters. C) We can observe the frictional effects of the hot gas in slowing the speeds of galaxies in the clusters. D) We detect this gas with X-ray telescopes.
Answer: D
8) Which of the following is not an observed characteristic of the cosmic microwave background? A) It has a perfect thermal radiation spectrum. B) Its temperature is the same everywhere, except for small variations at the level of 1 part in 100,000. C) Its temperature is a little less than 3 Kelvin (3 degrees above absolute zero). D) It contains prominent spectral lines of hydrogen, the primary chemical ingredient of the universe.
Answer: D
9) The Big Bang theory is supported by two major lines of evidence that alternative models have not successfully explained. What are they? A) (1) the theory correctly predicts that the universe should be expanding (2) the theory predicts the existence of and the specific characteristics of the observed cosmic microwave background B) (1) the theory predicts the episode of inflation that we think occurred in the early universe (2) the theory predicts the existence of large quantities of dark matter. C) (1) the theory correctly predicts that the universe should be expanding (2) the theory correctly predicts the observed ratio of spiral to elliptical galaxies in the universe. D) (1) the theory predicts the existence of and the specific characteristics of the observed cosmic microwave background (2) the theory correctly predicts the observed overall chemical composition of the universe.
Answer: D
9) Which of the following is not one of the three main strategies used to measure the mass of a galaxy clusters? A) measuring the speeds of galaxies orbiting the cluster's center B) studying X-ray emission from hot gas inside the cluster C) observing how the cluster bends light from galaxies located behind it D) measuring the temperatures of stars in the halos of the galaxies
Answer: D
11) Why might inflation have occurred at the end of the GUT era? A) Gravity was an extremely weak force at this period in time. B) Large amounts of matter and antimatter annihilated at this time. C) There wasn't enough matter present to slow down the expansion at that time. D) The universe was too small and needed to grow quickly. E) An enormous amount of energy was released when the strong force froze out from the GUT force.
Answer: E
19) Which of the following is not evidence for dark matter? A) the flat rotation curves of spiral galaxies B) the broadening of absorption lines in an elliptical galaxy's spectrum C) X-ray observations of hot gas in galaxy clusters D) gravitational lensing around galaxy clusters E) the expansion of the universe
Answer: E
25) Why do we think tiny quantum ripples should have been present in the very early universe? A) The shock wave of the Big Bang caused ripples that expanded outward with time. B) The energy released when the strong force froze out of the GUT force caused shock waves that produced ripples in the universe. C) Matter and antimatter particles that spontaneously formed from high-energy photons caused perturbations in the radiation field. D) The annihilation of matter and antimatter particles caused tiny explosions that perturbed the radiation field. E) Quantum mechanics requires that the energy fields at any point in space be continually fluctuating as a result of the uncertainty principle.
Answer: E
26) Which of the following are candidates for dark matter? A) brown dwarfs B) Jupiter-size objects C) WIMPs D) faint red stars E) all of the above
Answer: E
2) How long after the Big Bang was the Planck time, before which our current theories are completely unable to describe conditions in the universe? A) 10-10 second B) 10-35 second C) 10-43 second D) 3 minutes E) 300,000 years
C
