Deck 14: Modern Cosmology

Question 1

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.

Answer 1

no stable nuclei exist with masses of 5 or 8 hydrogen masses.

Question 2

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.

Answer 2

recombination.

Question 3

Dark energy 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.

Answer 3

force suspected to cause the current acceleration in the rate of expansion of the universe.

Question 4

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 5

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 6

In the late 1990's, it was discovered from distances of ______in distant galaxies that the expansion of the universe is ___________

A) Cepheid variables; accelerating
B) Cepheid variables; decelerating
C) supernovae; accelerating
D) supernovae; decelerating

Question 7

In the late 1990's, 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 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

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 10

Measured ages of globular clusters suggests that the universe is about

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

Question 11

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 consisting 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 cannot collide because the Coulomb barrier is too great.

Question 12

If gravity alone acts to retard the expansion and nothing acts to accelerate it, the universe is said to be closed if

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

Question 13

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) during 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 14

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.

Question 15

The cosmological principle states that the universe is

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

Question 16

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 17

The ____ view of the universe is that it is eternal and unchanging.

A) inflationary
B) accelerating
C) static
D) big bang

Question 18

The Hubble time is

A) the time it takes a galaxy moving at 1000 km/s 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 19

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 20

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 21

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 22

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 23

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 the Local Group.
D) all of the above.

Question 24

"Seeds" around which galaxies, clusters and walls grew may have been_____before inflation and recombination.

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 initially tiny quantum mechanical fluctuations in space-time

Question 25

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 26

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

Question 27

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 28

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 29

Possible equations (choose the correct one): $\tau$ =10¹²/H; H=v/d. If gravity is unimportant and H equals 75 km/s/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 30

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 31

Astronomers have found the center of the universe to be located in

A) Earth
B) the sun
C) Sagittarius A
D) the Virgo Cluster of galaxies
E) No center is thought to exist.

Question 32

Evidence for a very early "super rapid" inflation of the universe is that the 3-K radiation from opposite sides of the sky (180 degrees about 28 billion light years apart) is of nearly ________ intensity. Time for light to travel this distance is ________ the age of the universe in years.

A) equal; greater than
B) unequal; greater than
C) equal; less than
D) unequal; less than

Question 33

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 34

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 35

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 36

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 37

A frame of the HST deep field image of distant galaxies is shown. By means of optical and radio telescopes astronomers can see distant objects like these as they

A) are right now.
B) will be in the distant future.
C) were in the distant past.
D) all of the above.
E) none of the above.

Question 38

One explanation of the dark sky Olbers's Paradox is that light can reach us only from objects in space out to a distance in light years _______ the age of the universe in years.

A) less than
B) greater than
C) equal to
D) less than or equal to
E) greater than or equal to

Question 39

Astronomers believe that the hydrogen atoms in your body were created

A) in the planets.
B) inside the stars.
C) in the sun.
D) in the big bang.
E) in neutron stars.

Question 40

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

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

Question 41

How is Olbers's paradox explained?

Question 42

The deuterium and lithium-7 in distant quasars and in the interstellar medium suggests that the universe is open.

Question 43

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

Question 44

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

Question 45

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

Question 46

How old is the universe since the Big Bang? Pick the best answer according to radioactive dating in the solar system, light travel times to most distant galaxies, time reversal of the Big Bang, and observations of the 3-K radiation.

A) 1400 years
B) 14,000 years
C) 14,000,000 years
D) 14,000,000,000 years

Question 47

The elements hydrogen and helium were made during the first few minutes after the big bang.

Question 48

During its early history, matter dominated the universe.

Question 49

COBE and WMAP measure the temperature of the cosmic background radiation to be ____________________.

Question 50

The cosmic microwave background radiation was released shortly after the formation of the first stars.

Question 51

Observations of type Ia supernovae reveal that the expansion of the universe is speeding up because of the presence of ____________________ in empty space.

Question 52

The rate of expansion of the universe is currently increasing.

Question 53

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

Question 54

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

Question 55

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

Question 56

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

Question 57

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

Question 58

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

Question 59

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

Question 60

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

Question 61

How could the inflationary universe solve the horizon problem?

Question 62

How do we know there was a big bang?

Question 63

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

Question 64

Why would a value of 500 km/s/Mpc for the Hubble constant contradict theories of stellar evolution?

Question 65

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

Question 66

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

Question 67

Why is the primordial background radiation visible in all directions?

Question 68

What do the size and distribution of small scale temperature variations suggest about the geometry of the universe?

Question 69

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

Question 70

What is the difference between homogeneity and isotropy?

Question 71

What evidence do we have that the universe is expanding?

Question 72

Explain the important aspect(s) of the cosmological principle.

Question 73

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