Deck 11: Cosmology in the 21st Century

Question 1

Which of the following changes would make the raisin bread analogy more similar to the actual expansion of the universe?

A) Make the raisin loaf infinitely big.
B) Start with more of the raisins near the centre of the loaf.
C) Use a raisin loaf with the shape of a sphere.
D) Allow the raisin loaf to flatten out as it expands.

Answer 1

Make the raisin loaf infinitely big.

Question 2

What does the resolution of Olbers's paradox say about why it gets dark at night?

A) It gets dark at night because the universe is not infinite in age.
B) It gets dark at night because the universe is static.
C) It gets dark at night because the universe is closed.
D) It gets dark at night because the universe contains dust.

Answer 2

It gets dark at night because the universe is not infinite in age.

Question 3

About how many times larger are the wavelengths of CMB photons today compared to when they were first emitted?

A) 2
B) 10
C) 100
D) 1000

Answer 3

1000

Question 4

What is the approximate redshift of the CMB?

A) 0.1
B) 1
C) 10
D) 1000

Question 5

Why is the cosmic microwave background (CMB) so cold, if the early universe was so hot?

A) Enough time has passed for matter in the universe to release enough heat to cool down.
B) The CMB constantly interacts with atoms, which effectively cools down the photons.
C) The big bang was initially hot but the CMB was released from cold material much later on.
D) The expansion of the universe has redshifted those photons to an effectively cooler temperature.

Question 6

What is meant by the term "observable universe"?

A) the part of the universe that can be observed with current telescopes
B) the part of the universe where the look-back time is smaller than the age of the universe
C) the baryonic matter in the universe that can be observed with light
D) all of the matter that was created during the big bang

Question 7

What happens when a proton and an antiproton collide?

A) They destroy each other and produce energy in the form of gamma rays.
B) One of the protons is converted to a neutron and they form a nucleus of one proton and one neutron.
C) One of the protons is converted to an electron and they form a hydrogen atom.
D) One proton is converted to a neutron and the other is converted to an electron.

Question 8

If the Hubble constant were twice as large and the expansion rate was constant, what would be the approximate age of the universe?

A) 1 billion years
B) 7 billion years
C) 14 billion years
D) 28 billion years

Question 9

What happened when the average energy of gamma rays in the early universe was no longer high enough to create protons and neutrons?

A) Most of the protons combined with antiprotons.
B) Most of the protons combined with neutrons.
C) Most of the protons combined with electrons to form hydrogen atoms.
D) Most of the protons began to clump together due to their gravity.

Question 10

What is the point of the raisin bread analogy for the expanding universe?

A) to show that all observers see other raisins (galaxies) expanding away from them
B) to show that the raisins (galaxies) at the centre of the loaf have a special viewpoint
C) to show that there is an edge to the universe (the crust)
D) to show that the expansion is faster near the edges and slower in the centre

Question 11

Where did the cosmic microwave background (CMB) come from?

A) photons emitted from the first stars
B) photons released from hydrogen in our galaxy
C) light scattered by dust in our solar system
D) photons released when electrons and nuclei combined for the first time

Question 12

Approximately how long after the big bang did all four fundamental forces become distinct?

A) a thousand years
B) several minutes
C) several seconds
D) much less than one second

Question 13

When people hear the phrase "big bang," they often think of an explosion. What word would be a better description than "explosion"?

A) expansion
B) compression
C) combustion
D) extension

Question 14

Galaxy A is twice as far away as Galaxy B (both are very distant) and they happen to appear beside each other in the sky. What would observers in Galaxy A see?

A) Galaxy B and the Milky Way Galaxy would appear on opposite sides of the sky.
B) Galaxy B would have a greater redshift than the Milky Way Galaxy.
C) The Milky Way Galaxy would appear to be receding at twice the rate as Galaxy B.
D) The Milky Way Galaxy and Galaxy B would be approaching Galaxy A.

Question 15

Which of the following statements best describes Olbers's paradox?

A) The night sky should glow in predominantly X-ray wavelengths.
B) The night sky should glow bright.
C) The night sky should be always dark.
D) The night sky should glow in predominantly infrared wavelengths.

Question 16

What is the Hubble time?

A) the time it takes a galaxy moving at 1000 km/sec to move 1 Mpc
B) the time it takes the galaxy to double its distance from us
C) the time remaining before the universe stops expanding and begins to contract
D) an estimate of the age of the universe assuming a constant expansion rate

Question 17

Why is there a limit to the size of the observable universe?

A) because the universe has a finite radius
B) because galaxies appear to be moving away from us
C) because the sky is dark at night
D) because the universe has a finite age

Question 18

During the first moments of the big bang when elements could be created, nuclear fusion reactions made few heavy elements. Why not?

A) because all nuclei with masses greater than 4 hydrogen masses are unstable
B) because no stable nuclei exist with masses of 5 or 8 hydrogen masses
C) because the helium nucleus is unstable
D) because the temperature and density were too low

Question 19

If we lived in a static, unchanging universe, which of the following would you expect to see?

A) detection of the cosmic microwave background (CMB)
B) dark sky at night
C) galaxy properties that are constant with distance
D) redshift of galaxies that change with distance

Question 20

What property of an antiproton is opposite to that of a proton?

A) mass
B) velocity
C) electric charge
D) direction of spin

Question 21

A universe is finite in time if its expansion will eventually stop, and finite in space if it does not extend indefinitely. What would a closed universe be?

A) infinite in both time and space
B) finite in both time and space
C) infinite in time but finite in space
D) finite in time but infinite in space

Question 22

Which of the following is a characteristic of the first stars to form in the universe?

A) They belong to population I.
B) They are old M dwarfs.
C) They are metal poor.
D) Their spectra have strong absorption lines.

Question 23

Which of the following has the events in the universe's history in chronological order?

A) electron-positron annihilation, proton-antiproton annihilation, reionization, recombination
B) electron-positron annihilation, proton-antiproton annihilation, recombination, reionization
C) proton-antiproton annihilation, electron-positron annihilation, recombination, reionization
D) proton-antiproton annihilation, electron-positron annihilation, reionization, recombination

Question 24

What is the name for the period between when the CMB was emitted and when the first stars formed?

A) the Hubble time
B) the dark age
C) reionization
D) recombination

Question 25

Approximately how long after the big bang did the first galaxies and stars form?

A) a hundred years
B) a thousand years
C) a billion years
D) a million years

Question 26

How long after the big bang could gas begin to clump together due to gravity?

A) 30 min
B) 50 000 years
C) 400 000 years
D) 100 million years

Question 27

The cosmic background radiation comes from a particular time after the origin of the universe. What was that time?

A) when protons and neutrons were first formed
B) when the big bang first began to expand
C) when gamma rays had enough energy to destroy nuclei
D) when electrons began to recombine with nuclei to form atoms

Question 28

As the universe cooled, it eventually reached a temperature of 3,000 K and protons were able to capture and hold electrons to form neutral hydrogen. What is this process called?

A) recombination
B) isotropy
C) annihilation
D) ionization

Question 29

Why did electron-positron annihilation occur after proton-antiproton annihilation?

A) Electrons were created after protons.
B) Electrons have less mass than protons.
C) Electrons are negatively charged while protons are positively charged.
D) Electrons require higher-energy gamma rays to form.

Question 30

What was the temperature of the universe when the recombination took place that produced the cosmic background radiation we observe today?

A) about 2.7 K
B) about 300 K
C) about 3,000 K
D) about 3 billion K

Question 31

How does the geometry of a gravity-dominated universe relate to its density?

A) If the universe is closed, the density is equal to the critical density.
B) If the universe is flat, the density is equal to the critical density.
C) If the universe is open, the density is equal to the critical density.
D) if the universe is open, the density is greater than the critical density.

Question 32

What does a cosmological redshift tell you?

A) how fast a galaxy is moving away from us
B) the strength of gravity where the light was emitted
C) the amount of time dilation caused by a galaxy's motion
D) how much the universe has expanded since the light was emitted

Question 33

Which of the following applies if the universe is closed?

A) The universe will expand forever.
B) The universe has a centre.
C) The universe has an edge.
D) The universe has a high density.

Question 34

What is the assumption of homogeneity?

A) that the large-scale appearance of the universe is the same in all epochs
B) that the large-scale appearance of the universe is the same from any point
C) that the large-scale appearance of the universe is the same in every direction
D) that the large-scale appearance of the universe is the same at any temperature

Question 35

What characteristic of the universe governs whether the universe is open, closed, or flat?

A) density
B) temperature
C) radius
D) rotation rate

Question 36

What properties does the cosmological principle require the universe to have?

A) homogeneous and isotropic
B) homogeneous and expanding
C) isotropic and accelerating
D) isotropic and expanding

Question 37

Under what conditions will space-time be flat?

A) if the universe is expanding
B) if the universe is finite
C) if the average density of the universe is equal to the critical density
D) if the universe is homogeneous and isotropic

Question 38

Suppose you found a gas cloud, the atoms of which had never been part of a star. What would you expect its composition to be?

A) 100% hydrogen
B) 75% hydrogen and 25% helium
C) 70% hydrogen, 25% helium, and 5% other elements (carbon, oxygen, etc.)
D) 50% hydrogen and 50% helium

Question 39

Imagine three universes that have the same expansion rate and contain no dark energy: an open universe, a closed universe, and a flat universe. What can you say about the age of the open universe compared to the other two?

A) The open universe will be older than both the flat and closed universes.
B) The open universe will be younger than both the flat and closed universes.
C) All three universes will be the same age.

Question 40

What is the assumption of isotropy?

A) that the large-scale appearance of the universe is the same in all epochs
B) that the large-scale appearance of the universe is the same from any point
C) that the large-scale appearance of the universe is the same in every direction
D) that the large-scale appearance of the universe is the same at any temperature

Question 41

What property of the universe includes filaments, walls, and voids?

A) quantum fluctuations
B) large-scale structure
C) homogeneity
D) isotropy

Question 42

What is the current best determination of the Hubble constant?

A) about 0.07 km/sec/Mpc
B) about 7 km/sec/Mpc
C) about 70 km/sec/Mpc
D) about 700 km/sec/Mpc

Question 43

Which of the following best describes the horizon problem?

A) the nearness of the universe to critical density
B) the isotropy of the cosmic microwave background
C) the existence of the inflationary big bang
D) the limited size of the observable universe

Question 44

What is quintessence?

A) the force that led to the inflationary period of the universe
B) the theoretically hypothesized five-dimensional space of the universe
C) the theoretically hypothesized form of dark energy that can change in strength
D) the cosmological constant

Question 45

What does the flatness problem state?

A) that the universe is one-dimensional
B) that the density of the universe is much greater than the critical density
C) that the universe is two-dimensional
D) that the density of the universe is very close to the critical density

Question 46

The detections of gravitational waves by LIGO represented a striking confirmation of which theory?

A) general relativity
B) the big bang theory
C) inflationary theory
D) cosmic microwave background theory

Question 47

What elements would you measure the abundance of if you wanted to infer the amount of normal ("baryonic") matter in the early universe?

A) lithium and boron
B) carbon and oxygen
C) lithium and deuterium
D) hydrogen and helium

Question 48

Which of the following does current evidence suggest about the universe?

A) It is flat, infinite, and neither expanding nor contracting.
B) It is closed, finite, and its expansion is slowing.
C) It is open, infinite, and its expansion is slowing.
D) It is flat, infinite, and its expansion is accelerating.

Question 49

What do current observations indicate about the amount of baryonic matter and dark matter in the universe?

A) The total amount detected is sufficient to overcome the expansion of the universe.
B) The total amount detected implies that the universe is closed.
C) The amounts of the two kinds of matter are roughly equal.
D) The total amount detected implies that the universe is open.

Question 50

What could be the origin of the galaxy seeds around which galaxies, clusters, and walls grew?

A) hot dark matter
B) baryons
C) the separation of the electromagnetic and weak forces
D) quantum fluctuations in space-time

Question 51

How old was the universe when dark energy began to accelerate its expansion?

A) less than 1 second old
B) 400 000 years old
C) 1 billion years old
D) 8 billion years old

Question 52

What is the fate of an open universe that has no dark energy?

A) expansion forever
B) eventual collapse
C) gradual halt to the expansion
D) can't be known without density information

Question 53

What would be different if dark matter were "hot" rather than "cold"?

A) It would heat up baryonic matter.
B) It would be able to fuse hydrogen into helium.
C) It would be more uniformly distributed.
D) It would increase the temperature of the CMB.

Question 54

What is dark energy?

A) the energy associated with dark matter
B) the energy associated with the cosmic microwave background
C) the energy causing the universe to expand
D) the energy causing the universe's expansion to accelerate

Question 55

Which of the following correctly describes the history of the universe's expansion rate after inflation ended?

A) always accelerating
B) slowing down then accelerating
C) accelerating then slowing down
D) always slowing down

Question 56

What property of the cosmic microwave background indicates that the universe is flat?

A) the temperature of 2.7 K
B) the distribution of sizes of tiny irregularities
C) the isotropic nature of the radiation
D) the peak wavelength of 0.1 cm

Question 57

Why did Einstein say that the cosmological constant was his "biggest blunder"?

A) It made his equations unable to describe the universe.
B) When he introduced it, he didn't know about the expanding universe.
C) When he introduced it, he didn't know about the accelerating universe.
D) When he introduced it, he didn't know about the existence of galaxies.

Question 58

In 1998, it was announced that very distant type Ia supernovae were dimmer than expected based on their redshifts. What did this imply about the state of the universe?

A) The expansion of the universe is accelerating.
B) The universe must be closed.
C) The universe contains the critical density of dark matter.
D) The universe must be infinitely old.

Question 59

What problems are solved by the theory of inflation?

A) flatness and horizon
B) dark matter and dark energy
C) Olbers's paradox and the cosmological principle
D) homogeneity and isotropy

Question 60

What observation has prompted astronomers to ponder the possible existence of dark energy?

A) discovery of quasars
B) discovery of superclusters
C) supernovae appearing fainter than expected at large redshifts
D) uniform nature of the cosmic microwave background (CMB)

Question 61

When a proton meets an antiproton they annihilate each other and produce ___________ _____________.

Question 62

The inflationary theory of the universe may explain why the background radiation is so isotropic.

Question 63

The night sky is dark because the universe is not infinitely old.

Question 64

The part of the universe from which light has had time to reach Earth is called the ____________ ________________.

Question 65

The observation that the universe looks the same in every direction is called ____________________.

Question 66

The spectrum of the CMB has many peaks corresponding to emission lines.

Question 67

The set of interferometers that detected the first gravitational waves is called _________.

Question 68

What does the Large Hadron Collider have to do with cosmology?

A) It is accelerating electrons so that they can travel across the universe.
B) It is accelerating protons to energies like those in the very early universe.
C) Its superconducting magnets are the same temperature as most of the universe.
D) It will produce deuterium and helium by fusion, as in the very early universe.

Question 69

A universe can be infinite in space but finite in age.

Question 70

The cosmological principle states that any observer in any galaxy will see the same general features of the universe.

Question 71

Most of the elements heavier than helium were made during the first few minutes after the big bang.

Question 72

If the average density of the universe is less than the critical density, the universe is open.

Question 73

If the acceleration of the universe is caused by quintessence rather than the cosmological constant it will experience a ______ _______ in the far future.

Question 74

The redshifts of the galaxies imply that the universe is expanding and that we are at the centre.

Question 75

The ________________________ _____________________ is that the universe is both isotropic and homogeneous.

Question 76

Hubble's law implies that on large scales, all galaxies are receding from the centre of the universe.

Question 77

The amount of deuterium found in the universe suggests that the universe is open.

Question 78

During its early history, matter dominated the universe.

Question 79

A(n) ____________________ universe is infinite and would have a density equal to the critical density.

Question 80

The ____________ constant is believed to be responsible for the force causing the accelerating expansion of the universe.