Deck 17: Modern Cosmology and the Origin of Structure

Question 1

During inflation when the universe was approximately 1 second old,its size grew by a factor of 10³⁰.

Answer 1

False

Question 2

Even at its earliest moments,the universe had about as much structure in it as it has at the current time.

Answer 2

False

Question 3

The four fundamental forces of nature are gravity,electromagnetism,the weak force,and the strong force.

Answer 3

True

Question 4

The three fundamental forces of nature are gravity,electromagnetism,and the strong force.

Question 5

The force that binds three quarks together to make up a proton or neutron is called the weak force.

Question 6

Dark energy is a force that continually decreases the expansion rate of the universe.

Question 7

The fact that $\varOmega$ _mass + $\varOmega$ _$\wedge$ is very close to 1 means that its value has always been very close to 1.

Question 8

The ratio of the density in luminous matter to the critical density is 0.3.

Question 9

There are fluctuations in the CBR due to the fact that clumps of dark matter had already begun to form in the universe.

Question 10

The theory of inflation assumes that at some point in time dark energy will decay and the universe will expand rapidly by a factor of 10³⁰.

Question 11

The concept of inflation helps solve both the problems of the flatness of the universe and smoothness of the cosmic background radiation.

Question 12

In the superstring theory that successfully unites gravity and quantum mechanics,the universe must have 11 dimensions (10 spatial and 1 temporal).

Question 13

Observations of Type Ia supernovae in distant galaxies confirm that the expansion of the universe is decreasing over time.

Question 14

If the sum of the mass and energy density in the universe yields $\varOmega$ < 1 then the universe will recollapse in a Big Crunch.

Question 15

The ratio of the average density in all forms of matter (luminous and dark)in our universe to the critical density is approximately 0.3.

Question 16

If dark energy were to instantly cease,our universe would continue to expand forever.

Question 17

Current numerical models suggest that most of the universe is composed of hot dark matter.

Question 18

Directly after the Big Bang,the universe was filled with a variety of charged particles,antiparticles,and photons.

Question 19

As structure formed in the universe,galaxy-sized objects formed before cluster-sized objects.

Question 20

The weak force mediates the beta decay of neutrons into protons,electrons,and antineutrinos.

Question 21

The critical density of the universe is approximately equal to:

A) 1 proton/m³
B) 1 kg/m³
C) 1 M _$\oplus$ /m³
D) 1 M _$\odot$ /m³

Question 22

If $\varOmega$ _matter + $\varOmega$ _$\wedge$ = 1 today and dark energy was a cosmological constant,the universe will:

A) expand forever
B) slow its expansion but never reverse it
C) stop expanding and eventually collapse
D) oscillate between expansion and collapse

Question 23

The figure below shows scale factor R_U as a function of time over the age of the universe.Ignoring the presence of dark energy,which curve would represent a plausible open universe?

A) Curve A
B) Curve B
C) Curve C
D) Curve D

Question 24

What can simultaneously solve both the flatness and horizon problems in cosmology?

A) GUTs
B) Quantum mechanics
C) Inflation
D) Dark energy

Question 25

Why would it be very improbable for our universe to have $\varOmega$ _mass + $\varOmega$ _$\wedge$ = 0.9?

A) It would quickly evolve to have a much different value of $\varOmega$ _mass + $\varOmega$ _$\wedge$ .
B) In order to exist,every universe must have $\varOmega$ _mass + $\varOmega$ _$\wedge$ = 1.
C) We know $\varOmega$ _mass = 1,based on the average density of galaxies.
D) The fluctuation in the CBR tells us that $\varOmega$ _mass + $\varOmega$ _$\wedge$ = 0.7.

Question 26

The figure below shows scale factor R_U as a function of time over the age of the universe.Ignoring the presence of dark energy,which curve would represent a flat universe?

A) Curve A
B) Curve B
C) Curve C
D) Curve D

Question 27

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

Question 28

If the fate of the universe were determined SOLELY by what we currently know 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

Question 29

Current observations suggest that the density of luminous matter ( $\varOmega$ _luminous),all matter ( $\varOmega$ _matter),and dark energy ( $\varOmega$ _$\wedge$ )are:

A) " $\varOmega$ _luminous = 0.1, $\varOmega$ _matter = 0.3, $\varOmega$ _$\wedge$ = 0.7"
B) " $\varOmega$ _luminous = 0.02, $\varOmega$ _matter = 0.5, $\varOmega$ _$\wedge$ = 0.5"
C) " $\varOmega$ _luminous = 0, $\varOmega$ _matter = 0.1, $\varOmega$ _$\wedge$ = 0.9"
D) " $\varOmega$ _luminous = 0.02, $\varOmega$ _matter = 0.3, $\varOmega$ _$\wedge$ = 0.7"

Question 30

Why does the overall mass and energy density of the universe decide its ultimate fate?

A) The greater the density of the universe,the more black holes will form,which will devour surrounding material more quickly.
B) The greater the density of the universe,the more gravitationally bound the universe will be.
C) The greater the density of the universe,the more massive stars it will contain,and the faster it will evolve.
D) The greater the density of the universe,the more stars it will form over time and the longer the universe will last.

Question 31

The figure below shows scale factor R_U as a function of time over the age of the universe.Ignoring the presence of dark energy,which curve would represent a closed universe?

A) Curve A
B) Curve B
C) Curve C
D) Curve D

Question 32

The figure below shows scale factor R_U as a function of time over the age of the universe.Ignoring the presence of dark energy,which curve would represent an implausible open universe?

A) Curve A
B) Curve B
C) Curve C
D) Curve D

Question 33

Is Einstein's "biggest blunder" still considered a mistake?

A) No,the cosmological constant is nonzero.
B) Yes,the cosmological constant turned out to be zero.
C) Somewhat,because he could have predicted that the universe was expanding even before Hubble observed it.
D) Both a and c are correct.

Question 34

We currently find ourselves in the stelliferous era in the history of our universe.

Question 35

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

Question 36

In a closed (spherical)universe,the sum of the angles in a triangle is:

A) 180 degrees
B) < 180 degrees
C) > 180 degrees
D) 240 degrees

Question 37

How does the addition of a nonzero cosmological constant 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 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.

Question 38

The flatness problem arises because only a universe with __________ can have that value forever.

A) " $\varOmega$ _mass + $\varOmega$ _$\wedge$ = 0"
B) " $\varOmega$ _mass + $\varOmega$ _$\wedge$ = 1"
C) " $\varOmega$ _luminous + $\varOmega$ _$\wedge$ = 1"
D) " $\varOmega$ _luminous + $\varOmega$ _$\wedge$ = 0"

Question 39

If $\varOmega$ _matter = 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

Question 40

Due to the fact that we live in a universe with an accelerating expansion rate,the actual age of the universe is __________ the Hubble time.

A) larger than
B) smaller than
C) the same as
D) independent of

Question 41

Even with infinitely powerful telescopes,we can look back in time only until:

A) when galaxies were first formed
B) when hydrogen and helium were formed
C) when gravity was quantum mechanical
D) the time of recombination

Question 42

By the time the universe was 5 minutes old,approximately 24 percent of the normal matter in it had been turned into:

A) protons
B) neutrons
C) hydrogen
D) helium

Question 43

How would astronomers describe the antiparticle of an electron?

A) It would have the same mass but opposite charge.
B) It would have the same charge but opposite spin.
C) It would have the opposite charge and higher mass.
D) It would have the opposite spin and higher mass.

Question 44

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,but it would be completely composed of energy.

Question 45

Soon after the Big Bang,we believe 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) gravity
D) nucleosynthesis

Question 46

Which of the following CANNOT be dark matter?

A) Axions
B) Positrons
C) Photinos
D) Neutrinos

Question 47

Why is the fact that the cosmic background radiation (CBR)is very smooth considered a problem?

A) A universe as smooth as predicted by the CBR should not have formed as many galaxies as have been observed.
B) A universe as smooth as predicted by the CBR should have collapsed by now.
C) A universe as smooth as predicted by the CBR should be expanding much faster than we are now.
D) A universe as smooth as predicted by the CBR should never occur because quantum mechanical fluctuations would have been imprinted on it.

Question 48

About what was the temperature of the universe when a typical CBR photon was no longer able to spontaneously create an electron and positron pair?

A) 1000 K
B) 100,000 K
C) 1 million K
D) 1 billion K

Question 49

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 seven spatial dimensions are tightly wrapped around each other and have not expanded.
B) The other nine spatial dimensions are too small to be noticeable.
C) The other seven spatial dimensions undergo inflation and flatten themselves out.
D) The other nine spatial dimensions wrap around each other and form the temporal dimension.

Question 50

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 theory of everything
C) Around the time the strong force separated out of the grand unified theory
D) Around the time the weak force and electromagnetism separated

Question 51

Inflation happened:

A) when the universe was < 10^-33 s old
B) when the universe expanded by a factor of approximately 10³⁰
C) when the average energy of the vacuum of spacetime changed
D) all of the above

Question 52

When the universe was __________ old,approximately 24 percent of the normal matter in it had been turned into helium.

A) 5 minutes
B) 8 hours
C) 1,000 years
D) 4.5 billion years

Question 53

The standard model of particle physics is incomplete because it leaves which question(s)unanswered?

A) Why do neutrinos have mass?
B) Why is the strong nuclear force much stronger than the weak nuclear force?
C) How is gravity related to the other three fundamental forces?
D) All of the above

Question 54

In the superstring theory that successfully unites gravity and quantum mechanics,the universe must have:

A) 11 dimensions (10 spatial and 1 temporal)
B) 4 dimensions (3 spatial and 1 temporal)
C) 9 dimensions (8 spatial and 1 temporal)
D) 6 dimensions (3 spatial and 3 temporal)

Question 55

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 energy in the CBR becomes less than the mass of the unified force's carrier particles.
C) Dark energy becomes significant at later times and forces the two to split.
D) The spatial dimensions split and so must the forces.

Question 56

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 CBR.

Question 57

A grand unified theory unites which forces?

A) Only electromagnetism,weak nuclear,and strong nuclear
B) Only gravity and strong nuclear
C) Only electromagnetism,gravity,and weak nuclear
D) All four known forces

Question 58

Grand unified theories are very attractive because they can explain:

A) why the universe consists mostly of matter
B) why the Big Bang never made any antimatter
C) why we have five fundamental forces in the universe today
D) why the CBR is very smooth

Question 59

What does the large-scale structure of the universe look most like?

A) A sponge with many large holes
B) A loaf of wheat bread with many tiny holes
C) A plate of flat noodles
D) A jar of marbles

Question 60

Which of the following are NOT considered carrier particles used to mediate forces between other particles?

A) Photons
B) Gluons
C) Quarks
D) W+ particles

Question 61

What do astronomers believe will be the final state of our universe?

A) A "Big Crunch" in which everything collapses back in on itself
B) An ever-expanding universe filled with nothing but hydrogen and helium gas
C) A universe that stops expanding and is filled with nothing but white dwarfs,neutron stars,and black holes
D) An ever-expanding universe filled with photons and elementary particles

Question 62

What process is most responsible for shaping the large-scale structure of the universe?

A) Supernovae from the first generation of stars
B) Gravity
C) Matter/antimatter annihilation
D) Magnetic fields

Question 63

Structure formation in our universe:

A) proceeds from the top down
B) proceeds from the bottom and moves up
C) begins on all spatial scales at the same time
D) begins after clusters form

Question 64

We expect the galaxies that we see at a redshift of 4 will be __________ than galaxies today.

A) more irregular and redder
B) larger and redder
C) smaller and bluer
D) smaller and redder

Question 65

What will happen to the expansion of the universe in the future if: (a) $\varOmega$ > 1,(b) $\varOmega$ = 1,and (c) $\varOmega$ < 1?

Question 66

How much of the total mass of the universe is made up of hot dark matter?

A) 5 percent
B) 25 percent
C) 45 percent
D) 90 percent

Question 67

Structure formation in the universe proceeds hierarchically,meaning that:

A) large objects collapse then fragment to form smaller objects
B) large objects form at the same times as smaller objects
C) small objects collapse then merge to form larger objects
D) only small objects form and are stable over time

Question 68

Is the theory behind Type IV multiverses testable?

A) Yes,because if you wait long enough you can see past your current horizon.
B) Yes,because your universe is a part of a larger structure.
C) No,because the different multiverses cannot communicate with one another.
D) No,because quantum mechanics forbids it.

Question 69

Why can't dark matter halos collapse to be the same size as the visible parts of galaxies?

A) Dark matter can't dissipate its energy through collisions.
B) Dark matter is mostly made of mini-black holes.
C) Dark matter has much more angular momentum.
D) Dark matter annihilates when it begins to get that dense.

Question 70

We expect the kinds of galaxies that we see at a redshift of 4 (that is,when the universe was much younger)to be:

A) much like what we see today
B) smaller and much more irregular looking than today
C) smaller versions of what we see today
D) far more numerous but with fewer spiral galaxies

Question 71

In order from first to last,the specific eras in the universe's history are known as the:

A) primordial,stelliferous,degenerate,and dark eras
B) stelliferous,black hole,and entropy eras
C) primordial,stelliferous,black hole,and entropy eras
D) primordial,stelliferous,degenerate,black hole,and dark eras

Question 72

Why does the sum of $\varOmega$ _mass and $\varOmega$ _$\wedge$ determine the shape of our universe?

Question 73

Our current ideas on galaxy formation suggest that the visible parts of galaxies:

A) form first and are incorporated into dark matter halos later
B) form only in the densest parts of dark matter halos
C) can tell you the total size of the dark matter halo
D) can tell you everything about the formation history of that galaxy

Question 74

Which is NOT an ingredient needed to build a cosmological simulation of large-scale structure formation?

A) The spectrum of density fluctuations that quantum mechanics imprints on the early universe
B) The density of dark matter and luminous matter in the universe
C) The grand unified theory
D) The density of dark energy in the universe

Question 75

Why does the critical mass density of the universe depend on the value of Hubble's constant,H₀?

Question 76

What are two observations that when combined tell us that the universe has $\varOmega$ _mass + $\varOmega$ _$\wedge$ = 1 and is flat?

Question 77

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?

Question 78

We currently live in the universe during its:

A) era of stars
B) era of degeneracy
C) era of black holes
D) era of darkness

Question 79

If neutrinos have mass but do not interact much with normal matter,why can't they be the dominant form of dark matter in the universe?

A) Structure formation would have started with large objects fragmenting into smaller objects.
B) Structure formation would have started with small objects merging to form larger objects.
C) Neutrinos would decay over time and disappear,causing galaxies to fall apart.
D) Neutrinos would not gravitationally lens background galaxies.

Question 80

If the quantum fluctuations imprinted on the dark matter halos at the time of the formation of the CBR were ten times larger,galaxies would likely be:

A) smaller
B) larger
C) more numerous
D) nonexistent