Deck 14: Modern Cosmology

Question 1

The assumption of isotropy states that

A) the universe looks the same at all epochs.
B) the universe looks the same from all locations over sufficiently great distances.
C) the universe looks the same in all directions over sufficiently great distances.
D) all of the above
E) none of the above

Answer 1

the universe looks the same in all directions over sufficiently great distances.

Question 2

The universe is said to be closed if
I. gravity is strong enough to stop the expansion in a finite time.
II. the density of the universe is less than the critical density.
III. the universe is finite.

A) I II
B) I,III
C) II III
D) I, I, III
E) none of the above

Answer 2

I,III

Question 3

The cosmological principle states that the universe is
I. expanding.
II. accelerating.
III. homogeneous.
IV. isotropic.

A) I and II
B) III and IV
C) I and III
D) II and IV
E) I, II, III, and IV

Answer 3

III and IV

Question 4

If the universe is closed and finite, then

A) the universe will expand forever
B) the universe has a center
C) the universe has an edge
D) none of the above

Question 5

If the universe is closed and finite, then

A) the universe has a center and an edge.
B) the universe will expand forever.
C) the final fate of the universe will be very cold and of extremely low density .
D) the space-time of the universe is negatively curved.
E) none of the above

Question 6

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 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.
E) A proton and an antiproton can not collide because the Coulomb barrier is too great.

Question 7

During the first moments of the big bang when elements could be created, nuclear fusion reactions made few heavy elements because

A) all heavy nuclei are unstable.
B) no stable nuclei exist with masses of 5 or 8 hydrogen masses.
C) the helium nucleus is unstable.
D) the temperature and density were too low.
E) no nuclei heavier than helium could form since there weren t any electrons formed.

Question 8

Current observations indicate that the amount of baryonic matter and dark matter in the universe

A) is sufficient great enough to overcome the expansion of the universe.
B) implies that the universe is closed.
C) is mostly in the form of black holes and quasars.
D) are roughly equal.
E) implies that the universe is open.

Question 9

If the universe is closed, then its age will be

A) less than two-thirds of 1/H.
B) more than two-thirds of 1/H.
C) equal to 1/H.
D) equal to H squared.
E) equal to the square-root of H.

Question 10

The ________ theory was based on the assumption that the universe was eternal and unchanging.

A) inflationary
B) accelerating
C) steady-state
D) big bang

Question 11

The Hubble time is

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 size.
C) the time since recombination occurred.
D) the time remaining before the universe stops expanding and begins to contract.
E) an estimate of the age of the universe based on the Hubble constant.

Question 12

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. This process is known as

A) ionization.
B) isotropy.
C) annihilation.
D) recombination.
E) hydration.

Question 13

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) A force exists that we knew nothing about that causes the acceleration.
B) The universe must be closed.
C) The universe is finite.
D) The amount of dark matter must be greatly less than the amount of normal matter.
E) The universe must be infinitely old.

Question 14

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 3000 K
D) about 3 million K
E) about 3 billion K

Question 15

An open universe

A) has a negative curvature.
B) has zero curvature.
C) has a positive curvature.
D) is finite.
E) has a center.

Question 16

Quintessence is the name of the

A) force that lead to the inflationary period of the universe.
B) five dimensional space of the universe.
C) force suspected to cause the current acceleration in the rate of expansion of the universe.
D) one of the particles of dark matter related to WIMPs.
E) the force that holds the proton together.

Question 17

Measured ages of globular clusters suggests that the universe is about ...

A) 1.4 billion years
B) 14 billion years
C) 140 billion years old.

Question 18

The resolution of Olbers paradox suggests that it gets dark at night because

A) the universe is not infinite in age.
B) the universe is static.
C) the universe is closed.
D) a and b
E) all of the above

Question 19

Space-time will be flat if

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

Question 20

The assumption of homogeneity states that

A) the universe looks the same at all epochs.
B) the universe looks the same from all locations over sufficiently great distances.
C) the universe looks the same in all directions over sufficiently great distances.
D) all of the above
E) none of the above

Question 21

If gravity is unimportant, and H equals 75 km/sec/Mpc, then the age of the universe is about

A) 8.9 billion years.
B) 13 billion years.
C) 16.6 billion years.
D) 26 billion years.
E) 74 billion years.

Question 22

If galaxy A is four times more distant than galaxy B, then according to the Hubble Law, galaxy A will recede ____ than galaxy B.

A) 16 times faster
B) 4 times faster
C) 2 times faster
D) 1.2 times faster
E) 0.25 times faster

Question 23

What observational evidence supports the fact that our universe is static and unchanging?

A) Detection of the cosmic microwave background (CMB)
B) Dark sky at night
C) Redshift of galaxies
D) Evolution of galaxies with distance
E) None of the above

Question 24

The cosmic background radiation comes from a time after the origin of the universe

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

Question 25

If a galaxy is located at a distance of 18 Mpc and is found to have recessional velocity of 1170 km/sec, what is Hubble s constant based only on this galaxy?

A) 65 km/sec
B) 75 km/sec
C) 55 km/sec
D) 85 km/sec
E) 95 km/sec

Question 26

If a galaxy is found receding from us at 894 km/sec and it is located at a distance of 12 Mpc, what is the age of the universe if the universe is flat?

A) about 20 billion years
B) about 1.3 billion years
C) about 13 billion years
D) about 9 billion years
E) about 90 billion years

Question 27

The best determination of the Hubble constant using Cepheid variables found in distant galaxies by the Hubble telescope suggests

A) that the Hubble constant is about 0.07 km/sec/Mpc.
B) that the Hubble constant is about 7 km/sec/Mpc.
C) that the Hubble constant is about 70 km/sec/Mpc.
D) that the Hubble constant is about 700 km/sec/Mpc.

Question 28

Galaxy seeds around which galaxies, clusters, and walls grey may have been

A) caused by hot dark matter.
B) caused by baryons.
C) the result of the separation of the electromagnetic and weak forces.
D) the result of freezing water molecules shortly after the universe became transparent to photons.
E) caused by defects in space-time.

Question 29

Current evidence suggests that the universe is

A) flat, infinite, and neither expanding nor contracting.
B) closed, finite, and slowing its expansion.
C) open, infinite, and slowing in its expansion.
D) static with no expansion.
E) flat, infinite, and accelerating in its expansion.

Question 30

The age of the universe can be estimated or constrained from

A) the age of the oldest objects such as globular clusters
B) the distances of galaxies beyond our Local Group of galaxies
C) the rate of recession of the galaxies beyond Local Group
D) All of the above

Question 31

The density of the universe is

A) equal to the critical density if the universe is closed.
B) equal to the critical density if the universe is flat.
C) greater than the critical density if the universe is flat.
D) greater than the critical density if the universe is open.
E) none of the above

Question 32

What is the fate of an open universe?

A) Expansion forever
B) Eventual collapse
C) Gradual halt to the expansion
D) Can t be known without density information.

Question 33

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

Question 34

Which of the following is not an assumption of cosmology?

A) Isotropy
B) Universality
C) Congruency
D) Homogeneity

Question 35

The flatness problem and horizon problem

A) are solved if there was a sudden inflation of the universe at time before recombination occurred.
B) show that the universe can be described as static and unchanging.
C) show that dark matter must be a small fraction of the total mass of the universe.
D) imply that the universe was once much colder than it is now.
E) imply that the inflationary theory is incorrect.

Question 36

If the universe is flat

A) its age will be equal to 1/H.
B) its age will be equal two-thirds of 1/H.
C) the density of the universe is less than the critical density.
D) the density of the universe is greater than the critical density.
E) dark matter accounts for a small fraction of the density of the universe.

Question 37

If a two-dimensional universe has a negative curvature,

A) the area of a circle will be greater than πr²
B) the area of a circle will be equal to πr²
C) the universe is infinite.
D) the universe is finite but bounded.
E) the universe will have a center.

Question 38

Whether the universe is open, closed or flat depends on the ____ of the universe.

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

Question 39

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 40

The flatness problem states that

A) the density of the universe is very close to the critical density.
B) the density of the universe is much larger than the critical density.
C) the density of the universe is much less than the critical density
D) the universe is two dimensional
E) the universe is one-dimensional

Question 41

During its early history, matter dominated the universe.

Question 42

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

Question 43

What evidence do we have that the universe is expanding?

Question 44

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

Question 45

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

Question 46

The rate of expansion of the universe is currently increasing.

Question 47

The ____________________ are theories that unify the electromagnetic, weak and strong forces at extremely high energies.

Question 48

The measured temperature of the cosmic background radiation is ____________________.

Question 49

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

Question 50

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

Question 51

What is the difference between homogeneity and isotropy?

Question 52

The red shifts of the galaxies imply that the universe is expanding and that we are at the center.

Question 53

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 54

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

A) Discovery of quasars
B) Discovery of superclusters
C) Supernovae appear fainter than expected at large redshifts.
D) Uniform nature of the cosmic microwave background (CMB).

Question 55

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

Question 56

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

Question 57

____________________ are a form of dark matter that consists of very low mass stars and planets too faint to be seen.

Question 58

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

Question 59

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

Question 60

Upon what false assumption is Olbers paradox explained?

Question 61

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

Question 62

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

Question 63

How could the inflationary universe solve the horizon problem?

Question 64

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

Question 65

Why is the primordial background radiation visible in all directions?

Question 66

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

Question 67

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

Question 68

How can the big bang still be visible? In what form has it been detected?

Question 69

How do we know there was a big bang?