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Chapter 21: The
Expanding Universe
Learning
Objectives
Define the bold-faced vocabulary terms within the chapter.
21.1 The Cosmological Principle
Compare and contrast the meaning of homogenous
and isotropic.
Multiple Choice: 1, 2, 4, 10
Illustrate the meaning of “homogenous and
isotropic.”
Multiple Choice: 8
Short Answer: 1
Explain how the cosmological principle implies that there is
no center of the universe.
Illustrate why observers in a uniformly expanding space will
all observe Hubble expansion.
Multiple Choice: 3, 5, 6, 9, 11, 36
Short Answer: 2, 3, 4, 6, 7
Relate redshift to look-back time.
Multiple Choice: 7
Short Answer: 5, 8
21.2 The Universe Began in the Big Bang
Explain why Hubble expansion observed today implies the
universe was smaller and hotter in the past.
Multiple Choice: 29, 30, 31, 37, 56
Distinguish between Hubble expansion arising from the
expansion of space and its arising from an explosion flinging debris through
space.
Multiple Choice: 32, 33, 34, 35
Short Answer: 14
21.3 Expansion Is Described with a Scale
Factor
Characterize how the scale factor changes with time.
Multiple Choice: 45, 46, 47
Short Answer: 18, 19
Illustrate how expanding space leads to the redshift of light
from distant objects.
21.4 Astronomers Observe Cosmic Microwave
Background Radiation
Illustrate why we expect the universe to be filled with a
cosmic microwave background.
Multiple Choice: 55, 71
Short Answer: 20, 22
Relate the image seen in the cosmic microwave background to
the epoch of recombination of hydrogen.
Multiple Choice: 51, 58, 59, 70
Short Answer: 21, 23, 24, 25, 26, 27
Describe the observed characteristics of the cosmic microwave
background.
Multiple Choice: 49, 50, 60, 61, 62, 64, 65, 68
Short Answer: 28, 29, 30
Characterize the conditions in the early universe based on
the currently observed cosmic microwave background.
Multiple Choice: 48, 52, 53, 54, 57, 66, 67, 69, 72
Working It Out 21.1
Use Hubble’s law to estimate the age of the universe.
Multiple Choice: 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22,
23, 24, 25, 26, 27, 28
Short Answer: 9, 10, 11, 12, 13
Working It Out 21.2
Relate redshift to scale factor.
Multiple Choice: 38, 39, 40, 41, 42, 43, 44
Short Answer: 16, 17
Distinguish between different sources of classical and
relativistic redshift.
Short Answer: 15
MULTIPLE CHOICE
1.
What do astronomers
mean when they say that the universe is homogeneous?
a.
All stars in all
galaxies have planetary systems just like ours.
b.
The universe looks
exactly the same no matter what direction you look.
c.
Galaxies are generally
distributed similarly throughout the universe.
d.
Generally speaking,
there is little difference between conditions on Earth, in the Sun, or in outer
space.
e.
The universe looks the
same at all times in its history.
2.
What do astronomers
mean when they say that the universe is isotropic?
a.
Far away parts of the
universe look just like nearby parts.
b.
All galaxies are spiral
galaxies like our own.
c.
Intergalactic gas has
the same density everywhere in the universe.
d.
The laws of physics
apply everywhere in the universe.
e.
The universe looks the
same no matter what direction you look.
3.
According to Hubble’s
law, as the distance of a galaxy __________ its __________ increases.
a.
increases; luminosity
b.
increases; recessional
velocity
c.
decreases; luminosity
d.
decreases; recessional
velocity
e.
decreases; peculiar
velocity
4.
If we lived in a galaxy
1 billion light−years from our own, what would we see?
a.
a universe 1 billion
years younger than ours
b.
a universe 1 billion
years older than ours
c.
much the same universe
we see here
d.
a universe expanding at
a slower rate than we see from Earth
e.
a universe expanding at
a faster rate than we see from Earth
5.
The spectra of most
galaxies tell us that
a.
most galaxies appear to
be moving away from us.
b.
their light comes
predominantly from objects other than stars.
c.
most galaxies contain
clouds of gas that are absorbing their favorite wavelengths.
d.
galaxies in the past
rotated at a faster rate than they do today.
e.
galaxies are rushing
through space at high speeds.
6.
Why are some galaxies’
spectra blueshifted rather than redshifted?
a.
Some distant galaxies
are gravitationally lensed.
b.
Some distant galaxies
show the universe was contracting before the Big Bang started.
c.
Some nearby galaxies
have vigorous star formation and are much bluer than others.
d.
Some distant galaxies
have AGN at their centers.
e.
For some nearby
galaxies the attraction of Milky Way dominates over the Hubble expansion of
space.
7.
If the distance of a
galaxy at a redshift z = 0.5 is 1,900 Mpc, how many years back into the past are we
looking when we observe this galaxy?
a.
500 million years
b.
2 billion years
c.
6 billion years
d.
9 billion years
e.
10 billion years
8.
The cosmological
constant was somehow “artificially” introduced by Einstein in order to
a.
make the universe
stationary.
b.
explain the nature of
dark matter.
c.
explain the riddle of
black holes.
d.
explain the nature of
dark energy.
e.
create a more
interesting mathematical solution to his equations
9.
The spectrum of the
galaxy NGC 7512 reveals a receding velocity of about 7000 km/s. An observer in
that galaxy takes a spectrum of the Milky Way and measures
__________________________.
a.
the same 7000 km/s
receding speed
b.
only 1000 km/s, because
for that observer the Hubble expansion is a lot slower
c.
something that we
cannot possibly know, because the laws of physics apply only within the Milky
Way
d.
23,000 km/s, because
the speed of light has a different value for that observer
e.
no relative motion,
because we are in fact wrong; the universe is static end eternal
10.
In an imaginary
universe, astronomers find that there are thousands of galaxies within a few
million light years in all directions, but beyond those galaxies there is
nothing but empty space. Such a universe would be
a.
isotropic and
homogeneous.
b.
isotropic but not
homogenous.
c.
homogeneous but not
isotropic.
d.
neither homogeneous nor
isotropic.
e.
lacking any evidence
for the Big Bang.
11.
You measure the redshift
of a distant galaxy and find, using Hubble’s law and assuming a Hubble constant
of 70 km/s/Mpc, that its distance is 1 billion ly. Imagine that an observer in
that galaxy is measuring the recession speed of the Milky Way while you
measure. What would be the speed that the remote alien observer would record?
a.
700 km/s
b.
21,500 km/s
c.
3,400 km/s
d.
10,700 km/s
e.
6,300 km/s
12.
Astronomers use
galactic redshift as a measure of
a.
gravity.
b.
luminosity.
c.
velocity.
d.
mass.
e.
distance.
13.
The inverse of the
value of H0 gives a measurement in a unit of
a.
time.
b.
mass.
c.
density.
d.
size.
e.
luminosity.
14.
What would you predict
for the recession velocity of a galaxy whose distance (measured with the help
of Type Ia supernovae) is 42 Mpc?
a.
2940 km/s
b.
1.42 km/s
c.
205,800 km/s
d.
25,000 km/s
e.
386 km/s
15.
Estimate the time it
takes two galaxies to reach a presently measured separation of 55 Mpc.
a.
13.9 billion years
b.
250 million years
c.
4.6 billion years
d.
less than a second
e.
27 billion years
16.
If a galaxy has an
apparent velocity of 700 km/s, what is its distance if the Hubble constant is
70 km/s/Mpc?
a.
10 Mpc
b.
70 Mpc
c.
100 Mpc
d.
700 Mpc
e.
1,000 Mpc
17.
If the distance of a
galaxy is 10 Mpc, what is its recessional velocity if the Hubble constant is 70
km/s/Mpc?
a.
700 km/s
b.
1,000 km/s
c.
3,500 km/s
d.
5,000 km/s
e.
7,000 km/s
18.
Hubble originally estimated
the “Hubble constant” to be about 500 km/s/Mpc. What age of the universe would
such a number imply?
a.
2 billion years
b.
13.8 billion years
c.
16 billion years
d.
250 million years
e.
500 million years
.
19.
Which of the following
pairs of numbers for recession velocity of galaxies and distance to galaxies is
not correct?
a.
2,100 km/s, 30 Mpc
b.
4,200 km/s, 60 Mpc
c.
7,000 km/s, 100 Mpc
d.
5,600 km/s, 80 Mpc
e.
6,100 km/s, 340 Mpc
20.
You observe the
following three galaxies and measure their respective recession velocities: (A,
2,100 km/s); (B, 4,400 km/s); and (C, 3,050 km/s). Which of the following must
be true about these galaxies?
a.
A is smaller than B.
b.
A has more star
formation than C.
c.
B has more stars than
C.
d.
B is farther than A.
e.
They are all members of
the Local Group.
21.
If the slope of the
graph v vs. D is Ho, the slope of the D
vs. v graph is the
a.
age of the universe.
b.
cosmological constant.
c.
scaling factor of the
universe.
d.
temperature of the CMB.
e.
amount of dark energy
in the universe.
22.
If the Hubble constant
had a value that was half of its current measured value of 70 km/s/Mpc, the age
of the universe would be about
a.
7 billion years.
b.
14 billion years.
c.
22 billion years.
d.
28 billion years.
e.
33 billion years.
23.
Which of the following
would not immediately rule out a Hubble constant of 300 km/s/Mpc?
a.
the age of the Sun
b.
the age of the globular
clusters in the Milky Way
c.
the age of the coolest
known white dwarfs
d.
the age of a main
sequence star 50 times more massive than our Sun
e.
the age of our Milky
Way Galaxy
24.
A Hubble constant of 70
km/s/Mpc is the same as
a.
0.072 Gyr−1.
b.
13.9 km/s/ly.
c.
7 × 10−5 km/s/ly.
d.
0.014 km/s/ly.
e.
0.014 Gyr−1.
25.
Galaxy peculiar
velocities are typically about 300 km/s. How far away do you have to look in
order to see galaxies recessional velocities that are 10 times this peculiar
velocity?
a.
12 Mpc
b.
25 Mly
c.
37 Mpc
d.
43 Mpc
e.
52 Mpc
26.
If you found a galaxy
with an Hα emission line that had a wavelength of 756.3 nm, what would
be the galaxy’s distance if the Hubble constant was 70 km/s/Mpc? (Note that the
rest wavelength of the Hα emission line is 656.3 nm.)
a.
650 Mpc
b.
760 Mpc
c.
3,200 Mpc
d.
6,400 Mpc
e.
7,600 Mpc
27.
If the spectrum of a
distant galaxy is observed to have a calcium K absorption line that occurs at a
wavelength of 500.4 nm, what is this galaxy’s distance if the rest wavelength
of this absorption line is 393.4 nm? Assume the Hubble constant is 70 km/s/Mpc.
a.
720 Mpc
b.
850 Mpc
c.
1,200 Mpc
d.
2,500 Mpc
e.
3,700 Mpc
28.
In the figure shown
below, the upper spectrum is from hydrogen at rest in a laboratory, and the
lower spectrum is from a galaxy. How far away is this galaxy?
a.
110 Mpc
b.
170 Mpc
c.
230 Mpc
d.
280 Mpc
e.
340 Mpc
29.
Galaxies move away from
us in all directions because
a.
the force of gravity
increases with distance.
b.
the force of gravity
weakens with distance.
c.
space is expanding.
d.
our galaxy has expelled
all other galaxies.
e.
we are at the center of
the expansion of the universe.
30.
Hubble’s constant, H0,
represents the
a.
rate of expansion of
the universe.
b.
speed at which galaxies
are moving away from us.
c.
time it takes a galaxy
to move twice as far away from us.
d.
size of the universe.
e.
amount of time since
the Solar System formed..
31.
Choose the incorrect
statement about Hubble’s law.
a.
It allows us to measure
distances to remote galaxies.
b.
It is one fundamental
piece of evidence supporting the expansion of the universe.
c.
It provides information
about the age of the universe.
d.
It applies only to
nearby galaxies, within the Local Group.
e.
It is essentially a
linear proportionality between recession velocity and distance for galaxies.
32.
Where in the universe
did the Big Bang take place?
a.
near the Milky Way
Galaxy
b.
near the Virgo cluster
c.
near some unknown
location on the other side of the universe
d.
everywhere in the
universe
e.
at the center of the
universe, not too far from the center of the cosmic background radiation
33.
Hubble’s law is written
in a mathematical form as
a.
v × D = Ho.
b.
v × D = 1/Ho.
c.
v = Ho × D.
d.
v × Ho = D.
e.
D/v = Ho.
34.
Is dark energy
responsible for the expansion of the universe?
a.
No. The expansion would
happen without dark energy, but dark energy is causing the expansion rate to
decrease.
b.
Yes. Dark energy is
currently the driving force in the universe’s expansion.
c.
No. Dark energy is only
responsible for the observed rapid motions of stars within galaxies.
d.
No. The expansion would
happen without dark energy, but dark energy is causing the expansion rate to
increase.
e.
No. The dark energy has
no effect on the expansion.
35.
The apparent
recessional velocities of galaxies at large distances are due mainly to
a.
the actual motions of
the galaxies through space.
b.
the motion of our Sun
around the galactic center.
c.
a continuously
increasing scaling factor of the universe.
d.
the relativistic jets
launched by supermassive black holes.
e.
incorrect
interpretation of spectra from galaxies.
36.
An expanding universe
a.
was first predicted by
the general theory of relativity.
b.
was first discovered
observationally by Hubble and afterwards rejected on theoretical grounds.
c.
is just an abstract and
meaningless mathematical solution to a purely theoretical equation in
relativity.
d.
is at odds with the
cosmological principle.
e.
it is not consistent
with the predictions of the Big Bang model.
37.
If you measured the
distances and recessional velocities for a sample of galaxies and plotted the
data to get the figure shown below, what value would you derive for the Hubble
constant?
a.
10 km/s/Mpc
b.
50 km/s/Mpc
c.
70 km/s/Mpc
d.
100 km/s/Mpc
e.
500 km/s/Mpc
38.
Scientists indicate
that the first stars probably formed at a redshift z ~ 20. At that time the
universe was about
a.
5 percent of its
current size.
b.
50 percent of Earth’s
size.
c.
as big as an atom.
d.
about 100 AU across.
e.
the size of a
grapefruit.
39.
The universe was 10
percent its current size when light left objects observed now at redshift
a.
1.
b.
3.
c.
6.
d.
9.
e.
20.
40.
What is the correct
interpretation of a redshift larger than 1?
a.
The object is moving
faster than the speed of light.
b.
The universe has more
than doubled in size since the light from that object was emitted.
c.
The object has an
extremely large peculiar velocity.
d.
The light was shifted
to longer wavelengths from gravitational radiation.
e.
The rate of expansion
of the universe is increasing.
41.
When we look at
galaxies in the universe and measure their star formation rates, we find that
galaxies at redshifts z ≈ 1 have higher star formation rates than they do now. At that
time, the universe was __________ times the size it is today.
a.
0.1
b.
0.2
c.
0.5
d.
0.7
e.
0.9
42.
Distant galaxies we can
see today with a redshift of z ≈ 6 emitted their light when the universe was
a.
five times smaller than
it is today.
b.
six times smaller than
it is today.
c.
seven times smaller
than it is today.
d.
eight times smaller than
it is today.
e.
the same size as it is
today.
43.
The CMB is a snapshot
of the radiation in the universe at a redshift of z ≈ 1,000 when the
universe was about
a.
1,000 times smaller
than it is today.
b.
10 times smaller than
it is today.
c.
two times smaller than
it is today.
d.
the same size as it is
today.
e.
10 times larger than it
is today.
44.
The record for the most
distant galaxy in the universe was recently reported with a redshift of z =
8.68. Compared with the current size of the universe, what
was its size when the light from that galaxy started its long journey to us?
a.
about 10 times smaller
b.
about 50 percent
smaller
c.
about 0.001 percent
smaller
d.
about 99 percent
smaller
e.
about 250 percent
bigger
45.
Which of the following
are changing as the universe is expanding?
a.
the laws of physics
b.
the sizes of atoms
c.
the sizes of planetary
systems
d.
the cosmological
distances
e.
the diameters of stars
and galaxies
46.
Will the Sun get larger
over many billions of years?
a.
Yes, because of changes
taking place in its interior.
b.
Yes, because the rate
of expansion of the universe is increasing.
c.
No, because the Earth
is at center of the universe’s expansion.
d.
Yes, because the
expansion of the universe is pulling the Sun apart.
e.
No. It has always been
the same size.
47.
It is possible for a
galaxy to have an apparent velocity greater than the speed of light. This means
that the galaxy
a.
has an active nucleus
capable of producing relativistic jets.
b.
is approaching us and
the measured speed is a mere artifact of projecting its velocity along the line
of sight.
c.
has been ejected at
tremendous speed by the Big Bang.
d.
is being temporarily
accelerated by large numbers of simultaneous supernovae blasts.
e.
it is being carried by
the expansion of the universe.
48.
Which of the following
is not a prediction of the standard Big Bang theory that has been
successfully verified by observations?
a.
The universe is
expanding.
b.
The most distant
galaxies are redder because they are older.
c.
Helium and lithium were
made as the universe cooled after the initial Big Bang.
d.
The early universe was
very hot and dense.
e.
The most distant
galaxies are redder because their light has been stretched during the time it
took for the light to reach Earth.
49.
In the early 1960s,
physicists Penzias and Wilson detected a persistent noise at a wavelength of
about 1 mm in their radio telescope that came from all directions in the sky
due to
a.
synchrotron emission
from the Crab Nebula.
b.
emission from newly
formed stars in the Orion Nebula.
c.
cellphone usage.
d.
photons left over from
the Big Bang.
e.
television and radio
broadcasting.
50.
The temperature of the
CMB is hotter on one side of the sky than on the other by approximately 3 mK.
What does this tell us?
a.
The Earth has a
peculiar velocity of about 8,000 km/s with respect to the CMB.
b.
The Earth has a
peculiar velocity of about 400 km/s with respect to the CMB.
c.
The Earth is near the
center of the universe’s expansion but not exactly at the middle.
d.
The universe is
expanding faster on one side of us than on the other.
e.
The universe is
homogeneous but not isotropic.
51.
The oldest photons we
detect in the universe come from
a.
distant quasars.
b.
the first generations
of stars.
c.
the most distant
galaxies.
d.
the epoch of
recombination.
e.
the first supernovae.
52.
The cosmic microwave
background radiation was emitted when the universe had a size about 1/1000 of
today’s value. What was the temperature of the microwave background radiation
at the epoch of recombination?
a.
30 K
b.
300 K
c.
3000 K
d.
30,000 K
e.
300,000 K
53.
The existence of the
cosmic background radiation tells us that the early universe was
a.
much hotter than it is
today.
b.
much colder than it is
today.
c.
composed entirely of
radiation at early times.
d.
composed entirely of
stars at early times.
e.
about the same
temperature as today but much more dense.
54.
After the Big Bang, as
the universe cooled and protons and electrons combined, what important
consequence happened?
a.
Protons and neutrons
combined to form nuclei such as deuterium and helium.
b.
Neutrinos ceased to
interact with normal matter.
c.
Dark matter ceased to
interact with normal matter.
d.
Photons began to travel
freely through the universe.
e.
Lithium and other light
elements were formed by the fusion of hydrogen and helium.
55.
Does the temperature of
the cosmic background radiation by itself tell us anything significant about
the age of the universe?
a.
Yes, since it was
produced at a redshift of approximately 1,000.
b.
No, we still need to
know the Hubble constant to know the universe’s age.
c.
No, the temperature
does not, but the magnitude of temperature variations in the CMB does tell us
the age.
d.
Yes, in combination
with information on cosmic nucleosynthesis.
e.
No, the CMB formed at a
wide variety of times and gives no information on the age of the whole
universe.
56.
Choose the incorrect
statement about the CMB.
a.
It is nearly isotropic.
b.
It is a fundamental
confirmation of the Big Bang theory.
c.
It is a thermal
signature described by a temperature of about 3K.
d.
It was discovered
accidentally in the 1960s.
e.
It is thought to be
produced by the first generations of stellar black holes.
57.
The CMB can be regarded
as a “wall” beyond which we cannot see light because
a.
photons couldn’t leave
the hot plasma before the recombination period.
b.
we haven’t discovered
the technology to detect light from earlier epochs.
c.
galaxies absorb all the
photons from earliest times, closer to the Big Bang.
d.
there existed only massive
particles within the universe in the first 380,000 years of existence and no
photons.
e.
behind the CMB “wall”
there is a huge black hole that doesn’t allow light to escape.
58.
If the temperature of
the CMB changes with redshift z as T = T0(1
+ z), where T0 is the currently
measured 2.73K, what is the redshift corresponding to the time when the photons
first escaped from the 3000 K hot bubble of ionized material?
a.
about 10
b.
about 100
c.
about 1
d.
about 1000
e.
about 0.5
59.
How many times smaller
was the universe when the currently observed CMB photons started their journey
to us?
a.
1/1000
b.
1/10
c.
1/100
d.
1/10 5
e.
0.001 percent
60.
The COBE microwave map
shown in the figure below seems to indicate that one part of the sky is 0.003 K
warmer than the other. What is the cause of such an apparent anisotropy?
a.
Earth and Sun are
moving at 368 km/s in the direction of the constellation Crater relative to the
CMB frame.
b.
The map was obtained
when the Sun was at its peak of activity within a given 11−year cycle.
c.
It is due to
interference with the many microwave ovens people use in homes.
d.
The boundaries between
the warmer and cooler areas are sites of strong supernova activity.
e.
It indicates that
galaxies could form in only half of the universe.
61.
The apparently “grainy”
CMB distribution shown in the WMAP in the figure below represents temperature
fluctuations of about
a.
0.001 percent.
b.
0.1 percent.
c.
10 percent.
d.
50 percent.
e.
27.4 percent.
62.
The CMB fluctuations
seen in the WMAP temperature distribution measures are of crucial importance in
that
a.
they prove that the
cosmological principle is incorrect, the universe is in fact anisotropic.
b.
they reveal the
signatures of the large mass concentrations where subsequent galaxies and
clusters of galaxies formed.
c.
they reveal the
technical limitation of the detectors on board the WMAP satellite.
d.
they give us clues
about the black hole evaporation happening in the early universe.
e.
they emphasize the
limited value of general relativity.
63.
The CMB fluctuations of
0.001 percent seen in the WMAP sky map are due to
a.
gravitational
redshifts.
b.
technical artifacts.
c.
faulty instrumentation.
d.
Hubble expansion.
e.
explosive supernovae.
64.
The CMB spectrum shown
in the figure below is
a.
a thermal spectrum.
b.
an emission line
spectrum.
c.
an absorption line spectrum.
d.
identical to the
spectrum of our Sun.
e.
blueshifted into the
microwaves domain.
65.
Why is it not possible
to look all the way back to the Big Bang itself?
a.
Photons are not
produced until the stars begin to shine at a redshift of z ≈ 20.
b.
From redshifts of z
= 0 to 100, photons are gravitationally lensed by the dark
matter in the universe.
c.
At redshifts of z
> 1,000, most of the photons are blocked by large amounts of
cold gas and dust.
d.
For redshifts of z
> 1,000, photons cannot travel freely because they easily
interact with individual protons and electrons in the universe.
e.
Photons from the Big
Bang would be so strongly redshifted that we could never detect them.
66.
If the wavelength of
the background radiation peaked at 1 µm at the time of
recombination, how old was the universe then compared with its age today?
a.
one second old
b.
1/100th of a second old
c.
1/1,000th of a year old
d.
3,000 years old
e.
several hundred
thousand years old
67.
The current temperature
of the cosmic background radiation of 2.73 K means that the peak of its
spectrum occurs at a wavelength of
a.
0.1 µm.
b.
1 µm.
c.
10 µm.
d.
100 µm.
e.
1,000 µm.
68.
Why did the Big Bang
nucleosynthesis only produces elements less massive than lithium and beryllium?
a.
The universe expanded
and cooled rapidly.
b.
The universe was never
hot enough for nucleosythesis by fusion before stars formed.
c.
There was no black hole
to provide sufficient energy for advanced nucleosythesis.
d.
The laws of physics do
not allow the formation of massive nuclei outside stars.
e.
More massive elements
did form, but they decayed very fast into lighter ones.
69.
Which of the following
objects would be the oldest?
a.
a 4000K WD
b.
the Sun
c.
the CMB
d.
a 20 solar mass main
sequence star
e.
a halo star with 1/250
heavy element abundance relative to the Sun’s
70.
Which of the following
scientists is not directly connected to the prediction or discovery of the CMB?
a.
Arno Penzias
b.
Robert Wilson
c.
George Gamow
d.
Robert Dicke
e.
Georges Lemaître
71.
Which of the following
particles was not produced in the immediate aftermath of the Big Bang?
a.
hydrogen
b.
helium
c.
protons
d.
iron
e.
photons
SHORT ANSWER
1.
Describe the two
assumptions regarding the universe that the cosmological principle makes.
2.
We see the universe
around us expanding, at a rate of 70 km/s/Mpc. If you were an astronomer living
today in a galaxy that was located 1 billion light years away from us, at what
rate would you see the galaxies moving away from you?
3.
Does the expansion of
the universe make the Sun bigger? What about the Milky Way? Why or why not?
4.
Why did Einstein call
his cosmological constant his “biggest blunder”?
5.
The spectrum of a
galaxy is observed to have an Hα emission line at
a wavelength of 928.7 nm. What is its redshift? Note that the rest wavelength
of the Hα emission line is 656.3 nm.
6.
Does Hubble’s law imply
that our galaxy is sitting at the center of the universe? Explain.
7.
Imagine a balloon that
you can inflate to visualize the expansion of the universe. The space is
symbolized by the surface of the balloon. You use a marker to draw/paint
galaxies on its outside surface and you start pumping out air inside the
balloon. How would this model conform or not with the correct view of an
expanding universe?
8.
Explain the difference
between the universe and the observable universe.
9.
The spectrum of a
galaxy is observed to have an Hα emission line at
a wavelength of 856.3 nm. What is its distance if the Hubble constant is 70
km/s/Mpc? (Note that the rest wavelength of the Hα emission line is
656.3 nm.)
10.
Employing Hubble’s law,
calculate the distance to the Andromeda Galaxy, which is moving at 110 km/s.
The directly measured distance to Andromeda is 2.5 million light−years. How would
the two numbers agree or disagree. Explain.
11.
If the oldest known
globular clusters are about 13 billion years old, how is this constraining the
Hubble constant value?
12.
If the Hubble constant
were equal to 50 km/s/Mpc, what would the approximate age of the universe (the
Hubble time) be, assuming that the expansion rate has stayed approximately
constant over time? Note that 1 Mpc = 3.086 × 1019
km and 1 year = 3.154 × 107 s.
13.
Give two examples of
very old objects that could help astronomers set a lower limit on the age of
the universe.
14.
Why is the typical
visual depiction of the Big Bang in movies and television shows scientifically
incorrect?
15.
Explain the different
types of redshift you encountered in this chapter.
16.
The Hubble Space
Telescope can be used to study galaxies at a redshift equal to 2. How much has
the universe expanded since that light was emitted from these galaxies?
17.
You observe a distant
quasar in which the Lyman alpha line (Lα) of hydrogen
(rest wavelength = 121.6 nm) is found at a wavelength of 547.2 nm. When the
light from this quasar was emitted, how large was the universe compared to its
current size?
18.
What does the value of RU,
the scale factor of the universe, tell us?
19.
In the late 1940s,
various scientists hypothesized the existence of a background radiation, a
leftover signature from the Big Bang, although they also predicted a rather
cool temperature for it, in the range of 5−50K. Why did they
expect such a cold radiation to permeate the universe?
20.
Briefly explain how an
accurate determination of Hubbleconstant has improved our understanding of
cosmology.
21.
Why is the
“recombination” term used to describe the epoch when the universe became
transparent to photons sort of a misnomer?
22.
What are the three
different tests that support the Big Bang cosmology?
23.
If the temperature of
the CMB changes with redshift z as T = T0(1 + z), what
is the redshift corresponding to the time when the photons escaped from the hot
bubble of ionized material?
24.
If the temperature of
the CMB changes with redshift z as T = T0(1
+ z), and the recombination happened when the universe
was about 1,000 times smaller than at the present time, what was the
temperature at the time the universe became transparent to photons?
25.
If the temperature of
the CMB changes with redshift z as T = T0 (1
+ z), what was the peak wavelength of this
thermal/Plank signature when the universe was 1 percent of its current size?
26.
What important event in
the universe’s early history marked the creation of the cosmic background
radiation?
27.
Show in a graph format
how the scaling factor Ru changes with redshift.
28.
The cosmic microwave
background (CMB) has a temperature of approximately 2.73 K and a Planck
blackbody spectrum. Calculate the wavelength where the CMB spectrum peaks.
29.
What is the
significance of the 0.001 percent fluctuations detected in the CMP map by
modern satellites like WMPA and Plank, as in the figure shown below?
30.
The COBE and WMAP
satellites detected fluctuations in the CMB. On average, how big were these
fluctuations, and what do they that tell us about the universe at a redshift of
z = 1,000?
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Chapter 22: Cosmology
Learning
Objectives
Define the boldfaced vocabulary terms within the chapter.
22.1 Gravity and the Expansion of the
Universe
Illustrate why gravity determines the fate of the universe.
Multiple Choice: 1
Explain why density, rather than mass, determines the
evolution of the universe (i.e., expansion, contraction, acceleration,
deceleration).
Short Answer: 2
Relate the value of
the density parameter Ω to the evolution of the universe (i.e., expansion,
contraction, acceleration, deceleration).
Multiple Choice: 2, 3
Short Answer: 1
22.2 The Accelerating Universe
Summarize the evidence that there is a nonzero cosmological
constant.
Multiple Choice: 7, 8, 11, 13, 18, 19
Explain the effects of dark energy.
Multiple Choice: 6, 17
Short Answer: 4, 8, 12
Characterize how the amounts of matter and
dark energy in the universe determine its evolution and fate.
Multiple Choice: 12, 22, 23, 24, 27, 28, 30, 31, 32
Differentiate between the Big Crunch, Big Rip, and Big Chill.
Multiple Choice: 14, 15, 16, 20, 21
Short Answer: 11
Identify how gravity and dark energy influence the age of the
universe.
Multiple Choice: 9, 25
Short Answer: 5, 7
Illustrate the causes and behavior of different shapes
(geometries) of the universe.
Multiple Choice: 10, 26, 29
Short Answer: 6, 9, 10
22.3 Inflation Solves Several Problems in
Cosmology
Explain how inflation solves the horizon and flatness
problems.
Multiple Choice: 34, 35, 37, 38, 39
Short Answer: 16, 17, 18
Illustrate the effects of inflation on the early universe.
Multiple Choice: 36
Short Answer: 15
22.4 The Earliest Moments of the Universe
Connect the Very Largest Size Scales to the Very Smallest
List the four forces of nature.
Multiple Choice: 40, 46, 47, 48, 49, 50, 54, 64
Short Answer: 19, 21, 24
Illustrate the relationship between temperature of the
universe and unification of forces.
Multiple Choice: 44, 53, 61, 65, 66
Short Answer: 20
Explain how the events that occurred in the early universe
are related to the forces that operate in the universe today.
Multiple Choice: 43, 45, 51, 52, 57, 58, 59, 60, 62, 63, 67,
68
Short Answer: 22, 23, 25, 26
Illustrate the processes of pair production and annihilation.
Multiple Choice: 41, 42, 55, 56
Short Answer: 27
22.5 String Theory and Multiverses
Describe the motivation for string theory.
Short Answer: 29, 30
Assess whether string theory is a scientific theory.
Multiple Choice: 69, 70
Short Answer: 28
Assess whether multiverses are a scientific theory.
Multiple Choice: 71
Working It Out 22.1
Calculate the critical density of the Universe.
Multiple Choice: 4, 5
Short Answer: 3
Working It Out 22.2
Calculate the temperature and energy above which pair
production of different particles can occur.
Multiple Choice: 33
Short Answer: 13, 14
MULTIPLE CHOICE
1.
If there were no dark
energy in the universe, the value of __________ would solely determine the
evolution and fate of the universe.
a.
H0
b.
1/H0
c.
G
d.
Ωm
e.
ΩΛ
2.
If Ωm = 0.5 today and there were no dark energy, the universe would
a.
expand forever.
b.
slow its expansion but
never reverse it.
c.
stop expanding and
eventually collapse.
d.
oscillate between
expansion and collapse.
e.
expand so quickly that
the universe is ripped apart.
3.
If the fate of the
universe were determined solely by what is currently known to be
the total mass of the universe in luminous and dark matter (excluding dark
energy), astronomers would predict that we live in a universe that will
a.
expand forever.
b.
slow its expansion but
never reverse it.
c.
stop expanding and
eventually collapse.
d.
oscillate between
expansion and collapse.
e.
expand so quickly that
it will rip apart.
4.
If the Hubble constant
had a value of 50 km/s/Mpc, the value of the critical density ρc would be about
a.
twice larger.
b.
twice smaller.
c.
the same.
d.
1.4 times smaller.
e.
1.4 times larger.
5.
The critical density of
the universe is closest to
a.
6 protons/m3.
b.
5 g/m3.
c.
1 kg/m3.
d.
1 MEarth/m3.
e.
1 M⊙/m3.
6.
Gravity acts to
_________ the expansion of the universe, and dark energy acts to __________ the
expansion.
a.
slow down; slow down
b.
slow down ; speed up
c.
speed up; slow down
d.
speed up; speed up
7.
To determine how the
expansion rate of the universe has changed over time, astronomers directly
measure the _____________________ for a sample of Type Ia supernovae in distant
galaxies.
a.
redshift and luminosity
b.
redshift and brightness
c.
redshift and distance
d.
distance and luminosity
e.
distance and brightness
8.
The observations that
show that the expansion of the universe is speeding up tell us the universe
must contain
a.
gravity.
b.
dark matter.
c.
a force opposing
gravity.
d.
black holes.
e.
cosmic microwave
background radiation.
.
9.
What two properties of
the universe are determined by the values of Ωm and ΩΛ?
a.
size and temperature
b.
expansion rate and size
c.
size and age
d.
age and expansion rate
e.
age and temperature
10.
In a closed (spherical)
universe, the sum of the angles in a triangle is
a.
180 degrees.
b.
< 180 degrees.
c.
120 degrees.
d.
> 180 degrees.
e.
240 degrees.
11.
The accelerated
expansion of the universe was observationally discovered using
a.
Type Ia supernovae.
b.
Cepheid variables.
c.
RR Lyrae.
d.
stellar parallax.
e.
colors of galaxies.
12.
In a universe
undergoing an accelerated expansion,
a.
ΩΛ must be exactly zero.
b.
the fate of the
universe is exclusively dictated by Ωm.
c.
the mass density must
be larger than the critical density.
d.
the only possible
outcome is the Big Crunch.
e.
the age of the universe
is greater than the Hubble time.
13.
In modern cosmology,
Einstein’s cosmological constant is
a.
an example of dark
energy that causes an accelerated expansion of the universe.
b.
vanishingly zero.
c.
another name for the
critical density of the universe.
d.
the only explanation
for an infinite universe.
e.
of no use, as it
predicts a static universe.
14.
Which of the curves in
the figure shown below would best describe the scenario of a Big Rip for the
universe?
a.
A
b.
B
c.
C
d.
All three of them
e.
None of them
15.
Which of the curves in
the figure shown below would best describe the scenario of a Big Crunch for the
universe?
a.
A
b.
B
c.
C
d.
All three of them
e.
None of them
16.
In a scenario in which
dark energy is changing significantly over time, which of the following
outcomes are possible?
a.
Big Crunch and Big Rip
b.
Big Crunch and Big
Chill
c.
Big Rip and Big Freeze
d.
Big Crunch and Big
Freeze
e.
Big Chill and Big
Freeze
17.
Which of the following
is false?
a.
When the universe was
young, matter worked to slow the expansion rate of the universe.
b.
The Big Bang occurred
approximately 13.8 billion years ago.
c.
Only in the last 5 billion
to 6 billion years has dark energy caused the universe’s expansion rate to
increase over time.
d.
Throughout the age of
the universe, dark energy has caused its expansion rate to increase over time.
e.
Astrophysicists are
unsure whether or not dark energy always will continue to increase the
expansion rate of the universe.
18.
In the 1990s,
astronomers found that distant Type Ia supernovae were __________ than they
expected, leading them to conclude that ___________________.
a.
brighter; the
universe’s expansion rate was decreasing with time
b.
brighter; the universe
was finite in size
c.
fainter; the universe’s
expansion rate has been increasing with time
d.
fainter; the universe
was infinite in size
e.
fainter; the universe
was finite in size
19.
Observations of Type Ia
supernovae in distant galaxies have shown that
a.
the star formation rate
in galaxies decreases with increasing redshift.
b.
the expansion rate of
the universe is increasing.
c.
the cosmological
constant is zero.
d.
dark energy is
negligible at the present time.
e.
there were more stars
in the past than at the present time.
20.
The Big Rip could occur
in a universe where the effect of _____________ increases with time.
a.
quantum mechanics
b.
luminous matter
c.
dark energy
d.
gravity
e.
dark matter
21.
Current observations
suggest that the density of all matter and the density of dark energy are
a.
Ωm = 0.3; ΩΛ = 0.7
b.
Ωm = 0.02; ΩΛ = 0.5
c.
Ωm = 0.0; ΩΛ = 0.9
d.
Ωm = 0.7; ΩΛ = 0.3
e.
Ωm = 0.02; ΩΛ = 0.0
22.
What has had the
largest effect on the change in the expansion rate of the present-day universe?
a.
dark matter
b.
luminous matter
c.
dark energy
d.
radiation pressure
e.
gravity
23.
If Ωm + ΩΛ = 1 today and dark energy were a cosmological constant, the
universe would
a.
expand forever.
b.
slow its expansion but
never reverse it.
c.
stop expanding and
eventually collapse.
d.
oscillate between
expansion and collapse.
e.
expand so quickly that
the universe is ripped apart.
24.
How does the existence
of dark energy affect the expansion of the universe?
a.
It is possible for the
mass density of the universe to be below the critical density and still
collapse.
b.
It is possible for the
mass density of the universe to be below the critical density and still expand
forever.
c.
It is impossible to
have a collapsing universe, regardless of its density.
d.
It is impossible to
have an expanding universe, regardless of its density.
e.
It is impossible for
the mass density of the universe to be above the critical density and still
expand forever.
25.
In a universe
undergoing an accelerated expansion rate, the actual age of the universe is
__________ the Hubble time.
a.
older than
b.
younger than
c.
negligible compared
with
d.
the same as
e.
independent of
26.
The universe can be
infinite in size for which shapes of the universe?
a.
open
b.
closed
c.
flat
d.
closed and flat
e.
open and flat
27.
The figure below shows
a graph of the value of Ωm as a function of time
in a universe with no dark energy. The five different curves correspond to
universes with slightly different values for Ωm one second after the
Big Bang.
Which line corresponds to a universe with the largest value
of Ωm one second after the Big Bang?
a.
A
b.
B
c.
C
d.
D
e.
E
28.
The figure below shows
a graph of the value of Ωm as a function of time
in a universe with no dark energy. The five different curves correspond to
universes with slightly different values for Ωm one second after the
Big Bang.
Which line corresponds to a universe with the smallest value
of Ωm one second after the Big Bang?
a.
A
b.
B
c.
C
d.
D
e.
E
29.
Which of the following
statements is not valid?
a.
ΩΛ + Ωm = 1 indicates a flat universe.
b.
ΩΛ + Ωm = 1 ties into the flatness problem.
c.
ΩΛ and Ωm both affect the predictions about the fate and age of the
universe.
d.
In an open or closed
universe, Euclidian geometry is still applicable.
e.
Current observational
data seem to suggest that the universe is quite flat.
30.
The figure below shows
five graphs of the scale factor of the universe as a function of time. Which of
these graphs would occur for a universe with Ωm > 1 and ΩΛ = 0?
a.
A
b.
B
c.
C
d.
D
e.
E
31.
The figure below shows
five graphs of the scale factor of the universe as a function of time. Which of
these graphs would occur for a universe with Ωm < 1 and ΩΛ = 0?
a.
A
b.
B
c.
C
d.
D
e.
E
32.
The figure below shows
five possible graphs of the scale factor of the universe as a function of time.
Which of these graphs represent our universe where Ωm = 0.3 and ΩΛ = 0.7?
a.
A
b.
B
c.
C
d.
D
e.
E
33.
What was the
temperature of the universe when photons were no longer able to spontaneously
create electron and positron pairs? (Note that a photon’s energy is equal to 
, the cosmic background at any point in time
has a blackbody spectrum that peaks at a wavelength 
, and the mass of a single electron is 9.11 × 10-31
kg.)
, the cosmic background at any point in time
has a blackbody spectrum that peaks at a wavelength , and the mass of a single electron is 9.11 × 10-31
kg.)
a.
2,000 K
b.
400,000 K
c.
2 million K
d.
40 million K
e.
8 billion K
34.
The flatness problem
arises because only a universe with a value of __________ can have that value
forever.
a.
Ωm + ΩΛ = 0
b.
Ωm + ΩΛ = 1
c.
Ωm + ΩΛ = 0.7
d.
Ωm + ΩΛ = 0.02
e.
Ωm = ΩΛ = 0
35.
What can simultaneously
solve both the flatness and horizon problems in cosmology?
a.
GUT
b.
quantum mechanics
c.
TOE
d.
inflation
e.
dark energy
36.
Which of the following
is a false statement about inflation?
a.
Inflation occurred when
the universe was < 10−33 seconds old.
b.
Inflation occurred when
the universe expanded by a factor of approximately 1030.
c.
Inflation solves the
horizon problem.
d.
Inflation is currently
driving the expansion of the universe.
e.
Inflation solves the
flatness problem.
37.
Choose the correct
statement about inflation.
a.
It helps solve both the
problems of the flatness of the universe and the smoothness of the cosmic
background radiation.
b.
It assumes that at some
point in the future dark energy will decay and the universe will expand rapidly
by a factor of 1030.
c.
When the universe was
approximately 1 second old, its size grew by a factor of 1030.
d.
It is the best version
for a TOE.
e.
Scientists have
obtained direct and undisputable observational evidence that inflation did
occur.
38.
Why would it be very
improbable for our universe to have Ωm + ΩΛ = 0.9?
a.
It would quickly evolve
to have a much different value of Ωm + ΩΛ.
b.
In order to exist,
every universe must have Ωm + ΩΛ = 1.
c.
We know Ωm = 1, based on the average density of galaxies.
d.
The CMB fluctuations
tell us that Ωm+ ΩΛ = 0.7.
e.
Dark energy studies
tell us ΩΛ = 0.9.
39.
Why is the smoothness
of the cosmic microwave background radiation (CMB) considered a problem?
a.
A universe as smooth as
predicted by the CMB should not have formed as many galaxies as have been
observed.
b.
A universe as smooth as
predicted by the CMB should have collapsed by now.
c.
A universe as smooth as
predicted by the CMB should be expanding much faster than we are now.
d.
A universe as smooth as
predicted by the CMB should never occur, because quantum mechanical
fluctuations would have been imprinted on it.
e.
A universe as smooth as
predicted by the CMB should never have formed any stars or galaxies.
40.
Quantum chromodynamics
(QCD) describes how __________ works.
a.
gravity
b.
the strong nuclear
force
c.
electricity
d.
magnetism
e.
light
41.
The figure below
illustrates pair production in the early universe, with one particle labeled
with a question mark.
What type of particle must this be?
a.
proton
b.
electron
c.
Antiproton
d.
positron
e.
neutron
42.
What is the minimum
combined energy of the photons that would produce a pair of massive particles
electron-positron? (Note: me is the rest mass of an electron.)
a.
2mec2
b.
mec2
c.
1/2mec2
d.
E = mec2
e.
This cannot happen.
43.
A grand unified theory
(GUT) unites which forces?
a.
only electromagnetism,
weak nuclear forces, and strong nuclear forces
b.
only gravity and strong
nuclear forces
c.
only electromagnetism,
gravity, and weak nuclear forces
d.
only gravity and
electromagnetism forces
e.
all four known forces
44.
Scientists think that,
soon after the Big Bang, the four fundamental forces of nature were united into
one superforce, and __________ was the first to split off from the others.
a.
the strong force
b.
electromagnetism
c.
the weak force
d.
gravity
e.
nucleosynthesis
45.
Which list correctly
orders objects from the first one to form after the Big Bang to the last one to
form.
a.
neutral atoms, protons,
nuclei
b.
protons, nuclei,
neutral atoms
c.
nuclei, neutral atoms,
protons
d.
protons, neutral atoms,
nuclei
e.
nuclei, protons,
neutral atoms
46.
Which of the
fundamental forces in nature have an infinite range of action?
a.
electromagnetic and
gravity
b.
strong nuclear and
gravity
c.
strong and weak nuclear
d.
electromagnetic and
strong nuclear
e.
all four fundamental
forces have an infinite range of action
47.
What particles are the
carriers of the electromagnetic force?
a.
electrons
b.
magnetic monopoles
c.
gluons
d.
photons
e.
W+
48.
Which of the four
fundamental forces is the weakest of all?
a.
electromagnetic
b.
gravity
c.
weak nuclear
d.
magnetic
e.
strong nuclear
49.
Which of the four
fundamental forces governs the nuclear fusion inside stars?
a.
electromagnetic
b.
gravity
c.
weak nuclear
d.
magnetic
e.
strong nuclear
50.
What fundamental force
is responsible for holding the nucleons together inside atomic nuclei?
a.
electromagnetic
b.
gravity
c.
weak nuclear
d.
gluons
e.
strong nuclear
51.
Which of the following
is not true about the standard model?
a.
All particles are
created without mass.
b.
It is a complete
description of nature.
c.
Forces between
particles are mediated by carrier particles.
d.
Particles acquire mass
as they interact with the Higgs boson.
e.
Every particle in
nature has a corresponding antiparticle.
52.
Which of the following
would represent the unification of all fundamental forces?
a.
the electroweak theory
b.
quantum chromodynamics
(QCD)
c.
quantum electrodynamics
(QED)
d.
grand unified theories
(GUT)
e.
the Theory of
Everything (TOE)
53.
The TOE breaks within
___________ of the Big Bang.
a.
10-43 s
b.
10-35 s
c.
10-13 s
d.
15 s
e.
3 min
54.
Which of the following
are not considered carrier particles used to mediate forces
between other particles?
a.
photons
b.
gluons
c.
Zo particles
d.
quarks
e.
W+ particles
55.
How would scientists
describe the antiparticle of an electron?
a.
It would have the same
charge but opposite spin.
b.
It would have the same
mass but opposite charge.
c.
It would have the
opposite charge and higher mass.
d.
It would have the
opposite spin and higher mass.
e.
It would have the
opposite charge but same spin.
56.
In the very early
universe, which type of particles and antiparticles first stopped being
spontaneously formed out of photons any why?
a.
protons and neutrons,
because their formation requires a larger number of photons
b.
electrons and
positrons, because their formation requires a smaller number of photons
c.
protons and
antiprotons, because their formation requires higher energy photons
d.
electrons and
neutrinos, because their formation requires lower energy photons
e.
protons, antiprotons,
electrons, and neutrinos stopped forming at the same time.
57.
What would the universe
be like if there were complete symmetry between matter and antimatter?
a.
It would look similar
to our universe, but half of it would be composed of antimatter.
b.
We would observe two
universes, one an antimatter reflection of the other.
c.
There would be no
universe, because all of the matter and antimatter would have been annihilated.
d.
There would be a
universe devoid of matter, entirely composed of photons.
e.
It would look similar
to our universe, but the charges of all of the particles would be reversed.
58.
To verify whether or
not some grand unified theories are correct, physicists are searching for
a.
the Big Rip.
b.
mini−black holes.
c.
antimatter.
d.
protons that decay.
e.
dark matter that
decays.
59.
Grand unified theories
are very attractive because they can explain
a.
why we have five
fundamental forces in the universe today.
b.
why the Big Bang never
made any antimatter.
c.
why the universe
consists mostly of matter.
d.
why the CMB is very
smooth.
e.
what happens inside a
black hole.
60.
What is the Planck era?
a.
the earliest moments
after the Big Bang
b.
a period when quantum
mechanics is needed to describe both spacetime and particles
c.
the time period when a
theory of everything (TOE) is needed to understand the universe
d.
when spacetime can be
described as a quantum mechanical “foam” rather than a smooth sheet
e.
all of the above
61.
As the universe cooled
shortly after the Big Bang, which was the first fundamental force to separate
itself out from the others?
a.
electromagnetism
b.
gravity
c.
the nuclear force
d.
the strong force
e.
the weak force
62.
Which of the following
is an invalid statement?
a.
The inflation epoch
must have occurred before all four forces broke apart.
b.
Scientists have
confirmed the Grand Unified Theory by observing the decay of protons in
laboratory experiments.
c.
In the superstring
theory that successfully unites gravity and quantum mechanics, the universe
must have 11 dimensions (10 spatial and 1 temporal).
d.
The weak force mediates
the beta decay of neutrons into protons, electrons, and antineutrinos.
e.
The four fundamental
forces of nature are gravity, electromagnetism, the weak and the strong nuclear
forces.
63.
At what stage in the
universe’s history do we think the asymmetry between matter and antimatter was
created?
a.
at the very moment the
Big Bang occurred
b.
around the time gravity
separated out of the single superforce
c.
around the time the
strong force separated out of the grand unified theory
d.
around the time the
weak force and electromagnetism separated
e.
around the time the
electric and magnetic forces separated
64.
Which was a triumph of
quantum electrodynamics (QED)?
a.
QED predicted the
existence of three carrier particles before they were discovered in laboratory
experiments.
b.
QED unites the strong
and weak nuclear forces.
c.
QED is an example of a
theory of everything.
d.
QED successfully
explains the origin of quantum mechanical fluctuations in the CMB.
e.
QED combined the
electric and magnetic forces.
65.
The standard model of
particle physics is incomplete because it leaves which question(s) unanswered?
a.
Do neutrinos have mass?
b.
Why is the strong
nuclear force so much stronger than the weak nuclear force?
c.
Why was there an
imbalance between matter and antimatter?
d.
Does gravity have a
corresponding charge carrier?
e.
all of the above
66.
Why does a unified
force split to become two separate forces?
a.
The universe expands so
much that carrier particles become too dense.
b.
The average energy of
photons was not enough to produce particles mediating the interactions
c.
Dark energy becomes
significant at later times and forces the two to split.
d.
The spatial dimensions
split and so must the forces.
e.
Too many particles are
created for the unified force to manage.
67.
Even with infinitely
powerful telescopes, we can look back in time only until the time when
a.
galaxies first formed.
b.
hydrogen and helium
formed.
c.
stars first formed.
d.
gravity split off from
a superforce.
e.
recombination happened.
68.
Which of the following
have both been predicted and conclusively confirmed experimentally?
a.
the decay of proton
b.
the inflationary model
c.
the carrier particles
for the force of gravity
d.
the Higgs boson
e.
the 10 spatial
dimensions in superstring theory
69.
In the superstring
theory that successfully unites gravity and quantum mechanics, the universe
must have
a.
four dimensions (three
spatial and one temporal).
b.
six dimensions (three
spatial and three temporal).
c.
seven dimensions (six
spatial and one temporal).
d.
nine dimensions (eight
spatial and one temporal).
e.
eleven dimensions (10
spatial and 1 temporal).
70.
In some particle
physics theories, the universe must have more than three spatial dimensions,
but we experience only three. Why would we not see the other spatial
dimensions?
a.
The other nine spatial
dimensions are too small to be noticeable.
b.
The other seven spatial
dimensions are tightly wrapped around each other and have not expanded.
c.
The other seven spatial
dimensions undergo inflation and flatten themselves out.
d.
The other nine spatial
dimensions wrap around each another and form the temporal dimension.
e.
The other seven spatial
dimensions are completely full of dark matter.
71.
Which of these are
possible types of multiple universes that could exist?
a.
parallel universes with
different physics and different mathematical explanations
b.
other parts of an
infinite universe that are so far away that we cannot observe them
c.
quantum mechanical
parallel universes, which are created each time something happens that has a
probability of occurring in a different way, such as a roll of dice
d.
a multiverse with
constant inflation, where each universe forms due to quantum fluctuations
stopping that inflation
e.
all of the above
SHORT ANSWER
1.
In a universe with no
dark energy, what will happen to the expansion of the universe in the future if
(a) Ωm > 1, (b) Ωm = 1, and (c) Ωm < 1?
2.
Why does the critical
mass density of the universe depend on the value of Hubble’s constant, H0?
3.
The critical mass
density of the universe today is 9.5 × 10−27 kg/m3.
Using (only) the currently observed amount of luminous matter, what would be
the average mass density in the universe? If protons were spread evenly
throughout the universe, what would be their typical separation? (Note that the
typical separation between protons would be roughly equal to the cubic root of
the average volume occupied by one proton, and the mass of a proton is 1.67 × 10−27 kg.)
4.
If dark energy is
currently causing the expansion rate of the universe to increase with time,
does this mean that you should worry that the Sun, the Earth, and your body
itself are expanding? Why or why not?
5.
If you found a globular
cluster that had an age of 20 billion years, what cosmological observations
would conflict with this observation?
6.
Why does the sum of Ωm and ΩΛ determine the shape of our universe?
7.
If the Hubble constant
were larger than it is, how would that change the measured age of the universe?
Explain your answer.
8.
Outline the essential
difference between the view of the empty space employed by Friedmann and the
properties of the empty space in modern cosmology.
9.
Indicate two different
experiments that offer evidence for a flat universe.
10.
Summarize the possible
shapes of the universe and indicate if the Euclidian geometry is applicable in
each case.
.
11.
Briefly explain the
possible scenarios for the fate of the universe assuming that: (i) dark energy
decreases in time, (ii) it increases in time, and (iii) it is a constant.
12.
If there were enough
mass to slow down the expansion rate of the universe, how would the Hubble
constant measured using very distant galaxies be different from what is
observed in galaxies that are closer to us? Explain your answer. Is this what
we observe in our universe?
13.
Explain why the
production of electron-positron pairs requires less energetic photons than the
production of proton-antiproton pairs?
14.
What was the
temperature of the universe when photons were no longer able to spontaneously
create proton-antiproton pairs? (Note that a photon’s energy is equal to 
, the cosmic background at any point in time
has a blackbody spectrum that peaks at a wavelength 
, and the mass of a single proton is 1.67 × 10−27 kg.)
, the cosmic background at any point in time
has a blackbody spectrum that peaks at a wavelength , and the mass of a single proton is 1.67 × 10−27 kg.)
15.
Why does inflation not
violate the fundamental rule that nothing can travel through space faster than
the speed of light?
16.
What is the “flatness
problem” in cosmology?
17.
What can solve the
flatness and horizon problem in cosmology, and why?
18.
Explain what the
uncertainty principle means and how it relates to the horizon problem.
19.
What are the names of
the two particles that mediate the electromagnetic force in quantum
electrodynamics (QED) and the strong force in quantum chromodynamics (QCD)?
20.
What is the difference
between a grand unified theory (GUT) and a theory of everything (TOE)?
21.
Indicate the four
fundamental forces of nature by listing their names and describing what effect
each force has on objects in the universe.
22.
What is the main reason
that GUT theories are being pursued?
23.
Explain why the Higgs
bosons are important in the context of the standard model.
24.
In quantum
electrodynamics (QED), what mediates the electromagnetic force between
particles?
25.
Explain why astronomers
cannot accurately model the exact history of the universe in the first few
fractions of a second after the Big Bang.
26.
Outline two essential
problems/questions to which the standard model doesn’t offer an answer.
27.
How would the
antiparticle of the neutron be different from the neutron itself?
28.
Explain why the
superstring theory is considered more like a speculative idea or hypothesis
rather than a scientific theory.
29.
According to
superstring theory, how are different varieties of elementary particles
similar? How do they differ?
30.
Explain why inflation
could lead to an infinite number of multiverses inside our own universe. Are
they likely to be similar or different than our own universe?
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