Deck 11: Cosmology in the 21st Century

Question 1

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

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

Answer 1

homogeneous and isotropic

Question 2

Imagine three universes that have the same expansion rate and contain no dark energy: an open universe,a closed universe,and a flat universe.The open universe has its expansion slowed down less by the effects of matter than the closed universe or the flat universe does.Based on this,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.

Answer 2

The open universe will be older than both the flat and closed universes.

Question 3

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.

Answer 3

The total amount detected implies that the universe is open.

Question 4

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

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

Question 5

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)ionization
B)isotropy
C)annihilation
D)recombination

Question 6

What is quintessence?

A)the name of the force that led to the inflationary period of the universe
B)the name of the theoretically-hypothesized five-dimensional space of the universe
C)the name of the force suspected to cause the current acceleration in universe's expansion
D)the name of one of the particles of dark matter related to WIMPs

Question 7

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 8

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 9

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 10

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 based on the Hubble constant

Question 11

What does the resolution of Olbers' 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.

Question 12

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 13

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 14

In 1998,it was announced that the expansion of the universe is accelerating.What does this imply from the perspective of the Big Bang?

A)The acceleration is caused by a previously unknown force.
B)The universe must be closed.
C)The amount of dark matter must be far less than the amount of normal matter.
D)The universe must be infinitely old.

Question 15

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 16

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 17

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 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

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 20

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 21

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 22

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 23

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 expansion of the universe has redshifted those photons to an effectively cooler temperature.
D)The Big Bang was initially hot but the CMB was released from cold material much later on.

Question 24

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 25

What problems are solved by the theory of inflation?

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

Question 26

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 27

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 28

What is the current best determination of the Hubble constant?

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

Question 29

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 30

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 31

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 32

What does the flatness problem state?

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

Question 33

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

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

Question 34

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)redshift of galaxies that change with distance
D)galaxy properties that are constant with distance

Question 35

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

A)because the universe has a finite age
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 radius

Question 36

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 37

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 38

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 39

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

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

Question 40

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 41

How can the Big Bang still be visible? In what form has it been detected?

Question 42

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

Question 43

The rate of expansion of the universe is currently increasing.

Question 44

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

Question 45

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

Question 46

If the density of the universe is equal to the critical density,and H equals 50 km/sec/Mpc,then the true age of the universe is 13.3 billion years.

Question 47

Upon what false assumption is Olbers' paradox based?

Question 48

During its early history,matter dominated the universe.

Question 49

The deuterium in distant quasars and in the interstellar medium suggests that the universe is open.

Question 50

The ____________________ is that the universe is both isotropic and homogeneous.

Question 51

What evidence do we have that the universe is expanding?

Question 52

According to the steady state theory,the universe did not expand.

Question 53

How might we tell whether the universe is open or closed?

Question 54

What is the difference between homogeneity and isotropy?

Question 55

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 56

Most of the elements heavier than helium were made during the first few minutes after the Big Bang.

Question 57

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

Question 58

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

Question 59

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

Question 60

The measured temperature of the cosmic background radiation is ____________________.

Question 61

Describe how we know that the expansion rate of the universe is currently accelerating.

Question 62

Why is the primordial background radiation visible in all directions?

Question 63

How could the inflationary universe solve the horizon problem?

Question 64

How do we know there was a Big Bang?

Question 65

Explain why the principle of homogeneity is an important aspect of the cosmological principle.

Question 66

How could the measurement of the Hubble constant at great distances tell us whether the universe is open or closed?

Question 67

Why would a value of 100 km/sec/Mpc for the Hubble constant contradict theories of stellar evolution?