The Essential Cosmic Perspective, 8e (Bennett et al.)
Chapter 17 The Birth of the Universe
17.1 Multiple Choice Questions
1) What is the main idea of the Big Bang theory?
A) the idea that the universe formed from the collapse of a previous universe
B) the idea that all matter and energy in the universe began in an unimaginably dense state, and
then space itself began expanding in all directions
C) the idea that the universe as we see it formed from the singularity in a black hole
D) the idea that a massive explosion about 14 billion years ago created all matter and energy that
rushed out to fill the surrounding space
2)
This figure shows the temperature of the universe over time, according to the Big Bang theory.
At what age did the universe cool to 1 million degrees?
A) about 10–3 seconds after the Big Bang
B) about 1 second after the Big Bang
C) about 107 seconds after the Big Bang
D) about 1015 seconds after the Big Bang
3) We have direct experimental evidence (from large particle accelerators) for the physical
conditions in the universe back to about ________ after the Big Bang.
A) 1 million years
B) 380,000 years
C) 300 years
D) 3 minutes
E) 10-10 seconds
4) If the electromagnetic force is stronger than gravity, then why is it overpowered by gravity on
large scales?
A) The electromagnetic force only works on scales of about an atomic nucleus.
B) The electromagnetic force follows an inverse cube law with distance, rather than an inverse
square law.
C) Electrical charge is canceled out by mass.
D) Most objects are electrically neutral.
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.
6) How many forces operated in the universe during the GUT era?
A) One: a single, symmetric “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 four of the known forces
7) Which forces have physicists shown to be the same force under conditions of very high
temperature, 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
8) How long after the Big Bang was the Planck time, the time at which our current theories
become completely unable to describe conditions any earlier in the universe?
A) 10-10 seconds
B) 10-35 seconds
C) 10-43 seconds
D) 3 minutes
E) 380,000 years
9) 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.
10) 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 the antimatter that would have been produced at this
time.
C) We do not yet have a theory that links the weak and electromagnetic forces.
D) We do not yet have a theory that explains how the universe underwent a rapid period of
inflationary expansion.
E) The Planck era was the time before the Big Bang, and we cannot describe what happened
before the beginning of the universe.
11) What do we mean by inflation?
A) the expansion of the universe starting with the instant after the Big Bang
B) a sudden expansion of the universe driven by the energy released when the strong and
electroweak forces froze out from the GUT force
C) the rapid expansion of the universe, driven by white dwarf supernova, that we still observe
today
D) the sudden release of photons when particles and antiparticles annihilate each other
E) the photons released when electrons and protons first combined, forming the Cosmic
Microwave Background Radiation
12) Which event happened first (after the Big Bang)?
A) molecules formed
B) neutral atoms formed
C) protons formed
D) helium formed
13) 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 and electroweak forces froze
out from the GUT force.
14)
This figure shows the relative strength of the four basic forces as a function of temperature. At
what temperature does the strong force become distinct from the electroweak force?
A) about 1015 K
B) about 1027 K
C) about 1032 K
D) These forces were never unified.
15) What direct evidence do we have that the weak and electromagnetic forces were once unified
as a single force?
A) The most advanced telescopes are able to see back to the GUT era in the universe.
B) Detectors on Earth have received photons and high-energy particles from the GUT era.
C) Temperatures in the center of the Sun can reproduce the conditions during the Electroweak
era.
D) Particle accelerators on Earth can reach energies equivalent to the high temperatures of the
Electroweak era and have produced particles predicted by the unified theory.
E) We have no direct evidence of such a unified force.
16) What happened to all of 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.
17) Approximately how long did the nucleosynthesis era last?
A) 10-10 seconds
B) 0.001 seconds
C) 5 seconds
D) 5 minutes
E) 5 years
18) What kinds of atomic nuclei formed during the nucleosynthesis era?
A) only hydrogen
B) only helium
C) hydrogen, helium and trace amounts of lithium, beryllium, and boron
D) roughly equal amounts of hydrogen, helium, lithium, beryllium, and boron
E) essentially all of the chemical elements, except for those heavier than uranium
19) Why did the era of nucleosynthesis end?
A) The density of the universe became too low.
B) The temperature of the universe became too low.
C) Too many heavy elements were produced.
D) Neutrinos carried off too much energy.
20) Why is the nucleosynthesis era so important in determining the chemical composition of the
universe?
A) All the elements except hydrogen were produced in the nucleosynthesis era.
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 a small amount of elements heavier than helium produced later by stars, the
chemical composition of the universe is the same now as at the end of the nucleosynthesis era.
D) We can study the processes that occurred during the nucleosynthesis era to determine how
most of the elements in the universe were created.
E) By knowing how much matter was created during the nucleosynthesis era, we can determine
whether the universe is open or closed.
21) Why did the era of nuclei end when the universe was about 380,000 years old?
A) All the free particles had combined to form the nuclei of atoms.
B) The universe had expanded and cooled enough for stable, neutral atoms to form.
C) Atomic nuclei were finally able to escape the plasma of the early universe.
D) Photons were finally able to escape the plasma of the early universe and were no longer
available to produce hydrogen and helium nuclei.
E) The nucleosynthesis era that produced the nuclei heavier than helium ended.
22) Evidence that the cosmic background radiation is the remnant of a Big Bang comes from
predicting characteristics of remnant radiation from the Big Bang theory 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 2.73 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 redshifted emission lines from
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.
23) 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 that formed within the first billion years of the Big Bang.
C) It had a much higher temperature in the past.
D) It was discovered by Penzias and Wilson in the mid-1960s.
E) It appears essentially the same in all directions (it is isotropic).
24) From what cosmic epoch 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
25) 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 gas must be a perfect thermal radiation spectrum.
C) The spectrum of 75 percent hydrogen and 25 percent helium must be a perfect thermal
radiation spectrum.
D) The light from all the stars and gas in the sky averaged over the entire universe will be a
perfect thermal radiation spectrum.
E) It doesn’t predict that the cosmic background radiation should have a perfect thermal radiation
spectrum.
26) According to the Big Bang theory, why do we live in a universe that is made of matter rather
than antimatter?
A) 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.
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) 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.
27) 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 temperature over small angles.
C) Dark matter will smooth out the spectrum, but the small patches of “light” matter create
fluctuations in the temperature.
D) The overall structure of the universe is very uniform, but the synthesis of different elements
produces varying signatures within the background radiation.
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.
28) The cosmic microwave background peaks at a wavelength of about 1 mm, and the universe
has a temperature of about 3 K. If the microwave background peaked at a wavelength of 10
micrometers, what would its temperature be? (Hint: see Cosmic Calculations 5.1 and 17.1)
A) about 0.03 K
B) about 0.3 K
C) about 30 K
D) about 300 K
29) Helium originates from
A) only stellar nucleosynthesis.
B) only the Big Bang.
C) mostly from stellar nucleosynthesis with a small contribution from the Big Bang.
D) mostly from the Big Bang with a small contribution from stellar nucleosynthesis.
E) only radioactive decay of elements heavier than carbon.
30) Why did the Big Bang not produce heavier elements?
A) Too many high energy photons were present during the era of nucleosynthesis for heavy
elements to form.
B) By the time helium could survive, the temperature had become too low for heavier elements
to form.
C) They did, but radioactive decay caused these elements to disappear again.
31) What are two key observational facts that led to widespread acceptance of the Big Bang
model?
A) the cosmic background radiation and the helium content of the universe
B) the cosmic background radiation and the large scale structure 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 the universe
32) 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) The principles of quantum mechanics require that matter and antimatter particles formed from
high-energy photons continuously eject energy into the universe causing the ripples.
D) The annihilation of matter and antimatter particles caused tiny explosions that produced
ripples in the radiation field.
E) The principles of quantum mechanics require that the energy fields at any point in space be
continually fluctuating.
33) What is postulated to have caused a sudden inflation of the early universe?
A) the energy released from the annihilation of matter and antimatter
B) the energy absorbed by the separation of the electromagnetic and weak forces
C) the energy released from 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) the energy absorbed by giant quantum fluctuations
34) How does the theory of inflation explain the near-uniformity of the cosmic microwave
background?
A) The expanding universe would have cooled.
B) Matter expanded into regions of space that had no matter, and thus ended up at the same
temperature.
C) Matter was near the critical-density for a universal collapse, which smoothed out the
differences in temperatures.
D) Prior to rapid inflation, all regions of space were close enough to bounce radiation back-and-
forth and reach the same temperature.
35) Olbers’ paradox is an apparently simple question, but its resolution suggests that the universe
is finite in age. What is the simple question posed by Olbers’ paradox?
A) If space and time began with the Big Bang, what was there before that?
B) What caused the Big Bang?
C) How can a singularity have mass but no size?
D) Why is the sky dark at night?
E) Why are you always missing one sock from a pair after doing laundry?
36) What are the two possible explanations for not seeing something glowing brightly along
every line-of-sight in the sky?
I. The universe is infinite in size and infinitely old, but dust absorbs starlight from far away
stars.
II. The universe has a finite number of stars.
III. The universe is changing in some way as to prevent us from seeing an infinite number of
stars.
A) I and II
B) I and III
C) II and III
D) I, II and III
17.2 True/False Questions
1) In the cosmic timeline for the universe starting at the Big Bang, we live in the Planck era.
2) The Big Bang produced no elements heavier than helium because it was never hot enough for
helium to undergo fusion.
3) In the particle era, particles of matter outnumbered particles of antimatter by about 1 particle
in one billion.
4) The observed composition of ordinary matter in the universe—roughly 75 percent hydrogen
and 25 percent helium by mass—closely matches theoretical predictions based on the Big Bang
model.
5) A postulated inflationary era in which the early universe expanded in size by a factor of 1030
in approximately 10-36 seconds is incompatible with the theory of relativity because the universe
would have expanded faster than the speed of light.
6) If inflation really occurred, then our observable universe is only a tiny portion of the entire
universe born in the Big Bang.
7) Observations of the cosmic background radiation from the COBE satellite revealed tiny
variations in its temperature by about 1 part in 100,000.
8) The Big Bang predicts that the universe should be 25 percent hydrogen and 75 percent helium.
9) Recent measurements of the temperature fluctuations in the cosmic microwave background
radiation support the prediction of inflation that the overall geometry of the universe is flat.
10) The formation of galaxies would not have been possible without the tiny density
perturbations that formed prior to the inflationary period.
17.3 Process of Science Questions
1) The Cosmic Microwave Background Radiation: The CMB is one of the true observational
bonanzas of 20th– and 21st-century astronomy. Make as complete a list as possible of the various
observations of the cosmic microwave background that have been used to confirm, challenge,
and extend the Big Bang theory for the origin and evolution of the universe.
2) Evidence for Inflation: What is the observational evidence the universe underwent a brief but
very rapid period of inflation at the end of the GUT era, early in the history of the universe?
Does any of this evidence count as direct observational evidence? Does the validity of the Big
Bang depend on inflation being correct?
3) Falsifying a theory: The steady state universe was an alternate hypothesis to the Big Bang.
Summarize this hypothesis, and explain the two observations which disproved it.
17.4 Short Answer Questions
1) Briefly explain how Hubble’s discovery of a relationship between galactic distance and
redshift led to the idea of the Big Bang. (Hint: review chapter 16)
2) What do we mean by inflation, and why might it have occurred at the end of the GUT era?
3) Why is the era of nucleosynthesis so important in determining the chemical composition of
the universe?
4) Briefly explain why radiation was trapped for 380,000 years during the era of nuclei, and why
the cosmic background radiation was formed at the end of this era.
5) The discovery of the expansion of the universe led to the realization that everything must have
been in one place at one time, which gave rise to the Big Bang theory. Briefly describe the two
key pieces of evidence, other than expansion, that support the Big Bang theory.
6) What did the COBE, WMAP and Planck satellites find regarding the smoothness of the
cosmic background radiation?
7) Why weren’t many elements heavier than helium produced during the nucleosynthesis era?
8) What is Olbers’ paradox, and what is its resolution?
9) Briefly describe one of the three features of the universe that was left unexplained by the
standard Big Bang theory, but is explained by inflation. That is, describe either the structure
problem, the uniformity (or smoothness) problem, or the density (or flatness) problem.
17.5 Mastering Astronomy Reading Quiz
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) 10-45 seconds after the Big Bang
B) 380,000 years after the Big Bang
C) one ten-billionth of a second after the Big Bang
D) 10 billion years ago
2) What happens when a particle of matter meets its corresponding antiparticle of antimatter?
A) They fuse to make a heavier particle.
B) The question makes no sense, since antimatter does not really exist.
C) They can form a complete atom.
D) The combined mass of the two particles is completely transformed into energy (photons).
3) What is the significance of the Planck time?
A) Before it, conditions were so extreme that our current understanding of physics is insufficient
to predict what might have occurred.
B) It is the time when the cosmic microwave background was released.
C) It is the time at which inflation is thought to have occurred.
D) It is the amount of time required for two protons to fuse to make deuterium.
4) The four fundamental forces that operate in the universe today are ________.
A) nuclear force, electromagnetic force, gravity, tidal force
B) strong force, weak force, electromagnetic force, gravity
C) strong force, weak force, electric force, magnetic force
D) nuclear force, gravity, electric force, magnetic force
5) What property of the universe is uniquely predicted by the Big Bang theory?
A) the existence of both spiral and elliptical galaxies
B) the existence of cosmic background radiation
C) the existence of elements heavier than helium
D) the existence of the solar system
6) What do we mean by inflation in the context of the Big Bang theory?
A) the sudden release of photons when a particle and antiparticle annihilate one another
B) the expansion of the universe that we still observe today
C) 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
D) 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
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 very rapid 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 five 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) 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.
D) 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.
8) Which statement about the cosmic microwave background is true?
A) It is radiation that began its journey to our telescopes at the end of the nucleosynthesis era.
B) It is the result of a mixture of radiation from many independent sources, such as stars and
galaxies.
C) Its spectrum corresponds to a temperature of about 30 degrees above absolute zero.
D) With the exception of very small variations, it appears essentially the same in all directions in
which we look into space.
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 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.
B) (1) The theory predicts the existence of large quantities of dark matter; (2) the theory predicts
the existence of and the specific characteristics of the observed cosmic microwave background.
C) (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.
D) (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.
10) Which of the following observations cannot be explained by the Big Bang theory unless we
assume that an episode of inflation occurred?
A) the existence of the cosmic microwave background
B) the fact that about 25% of the ordinary matter in the universe consists of helium
C) the fact that the temperature of the cosmic microwave background is almost the same
everywhere
D) the fact that the universe is expanding
11) Why is the sky dark at night?
A) because of the vast distances between the galaxies
B) because dark matter fills the spaces between the galaxies and blocks their light
C) because there are dark dust clouds blocking the light of distant stars
D) because the universe is not infinitely old, so the distance we can see is limited
12) What is the temperature of the universe today?
A) 3000 K
B) 300 K
C) 3 K
D) The universe cannot be said to have a temperature.
13) Which of the following statements cannot be tested by science today?
A) Our universe is flat.
B) The universe is 14 billion years old.
C) Prior to the Planck time, our universe sprouted from another universe.
D) The expansion of the universe is now accelerating.
17.6 Mastering Astronomy Concept Quiz
1) How do we determine the conditions that existed in the very early universe?
A) We work backward from current conditions to calculate what temperatures and densities must
have been when the observable universe was much smaller in size.
B) 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.
C) 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.
D) We can only guess at the conditions, since we have no way to calculate or observe what they
were.
2) Which of the following observations (if made) would disprove an important prediction of the
Big Bang theory?
A) the discovery of a star with no elements heavier than hydrogen and helium
B) the discovery of a galaxy with 10% helium abundance
C) the discovery that some lithium was created during the nucleosynthesis era
D) the discovery of a galaxy with 30% helium abundance
3) Which of the following statements best explains what we mean when we say that the strong
force “froze out” at 10–38 second after the Big Bang?
A) This force first became distinct at this time.
B) This force is 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) This force caused the material in the universe to behave like a solid for a brief instant at this
time.
D) Following this time, the force was never important in the universe again.
4) According to the Big Bang theory, how many forces, and which ones, operated in the universe
during the GUT era?
A) 2 forces: gravity and a single force that later became the strong, weak, and electromagnetic
forces
B) 1 force that represented the unification of all four forces that operate today
C) 3 forces: gravity, the strong force, and the electroweak force
D) 2 forces: the strong force and the electroweak force
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
6) What was the significance of the end of the era of nucleosynthesis, when the universe was
about 5 minutes old?
A) The basic chemical composition of the universe had been determined.
B) The proportions of dark matter and luminous matter 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.
7) According to the Big Bang theory, why do we live in a universe that is made 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 was 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.
8) Why is the Big Bang theory the only theory of the universe you learn about in a typical
astronomy class?
A) Belief in the Big Bang theory is an important characteristic of an educated person.
B) Astronomers dismiss alternative theories because they don’t like them.
C) No competing theory has survived the test of evidence.
9) In principle, if we could see all the way back in time 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.
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
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.
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 would have caused random, tiny quantum fluctuations in energy fields to grow into
the density differences in the primordial gas from which galaxies formed.
B) Inflation predicts that gravity would have been very strong and thereby would have
concentrated mass into seeds.
C) Inflation tells us that the universe should have a “flat” overall geometry, and this led to the
flat disks of galaxies.
D) Inflation predicts that temperatures and densities should have become nearly equal throughout
the universe.
13) Which of the following is not consistent with observations of the cosmic microwave
background?
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.
14) 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) small
B) dense
C) hot
D) filled with intense radiation
15) 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 galaxy with a hydrogen abundance of only 50% by mass
B) the discovery of a star-like object made entirely of carbon and oxygen
C) the discovery of a planet that with no helium in its atmosphere
D) the discovery of a galaxy with 27% helium rather than the 25% that theory tells us was
produced in the Big Bang