Deck 18: Cosmology

Question 1

If Hubble's constant is actually half the value we believe it to be (70 km/(s/Mpc)), the Universe would be...

A) twice as old as we think it is.
B) half as old as we think it is.
C) four times as old as we think it is.
D) the same age.

Answer 1

twice as old as we think it is.

Question 2

The age of the Universe can be deduced from...

A) Hubble's law.
B) Kepler's Third law.
C) the Doppler shift law.
D) the Inverse-square law.
E) Shapley's law.

Answer 2

Hubble's law.

Question 3

The study of the structure and evolution of the Universe is called ______.

A) anthropology
B) cosmology
C) astrology
D) archaeology

Answer 3

cosmology

Question 4

___________ provides experimental evidence that the Universe is expanding.

A) The Big Bang model
B) The cosmological constant
C) Hubble's law
D) Dark matter

Question 5

The inverse of Hubble's constant (1/H) gives the approximate ______________.

A) size of the Universe
B) age of the Universe
C) magnitude of the cosmic horizon
D) density of the Universe

Question 6

According to the present estimates, the Universe is about ______ years old.

A) 14 × 10⁵
B) 14 × 10⁷
C) 14 × 10⁹
D) 14 × 10¹¹

Question 7

The Cosmological Principle states that

A) the Universe began as a hot violent event.
B) there is not a preferred location in the Universe.
C) the expansion of the Universe is speeding up.
D) the Universe will continue to expand forever.
E) the laws of physics apply everywhere in the Universe.

Question 8

When astronomers use Hubble's law to measure the distance to a galaxy they have to measure the ______ of the galaxy.

A) mass
B) luminosity
C) recessional speed
D) rotational speed

Question 9

Why does the observation that all distant galaxies are moving away from Earth not violate the Cosmological Principle?

A) Any other galaxy in the Universe will also see the Universe expanding in the same way.
B) The night sky is still dark.
C) The motion of galaxies relative to Earth has nothing to do with the Cosmological Principle.
D) It does violate the Cosmological Principle but for only the location of Earth.

Question 10

How do astronomers estimate the approximate age of the Universe?

A) The age of the Universe is equal to the Hubble constant (H).
B) The age of the Universe is equal to 1/H.
C) The age of the Universe is approximately the age of our Sun.
D) They measure the distance to the cosmic horizon and divide by the speed of light.

Question 11

Suppose the Hubble constant turned out to be 130 km/sec/Mpc and not 65 km/sec/Mpc. How would that affect our estimate of the age of the Universe?

A) The Universe would be about 30 billion yrs old.
B) The Universe would be about 7 billion yrs old.
C) The Universe would be about 130 billion yrs old.
D) It would have no effect on our estimates of the Universe's age.
E) None of these choices is correct.

Question 12

Dividing the separation of two galaxies by their recession speed is a simple way to estimate...

A) the density of the Universe.
B) if the Universe is flat.
C) if the Universe contains dark matter.
D) the age of the Universe.
E) the temperature of the CMB.

Question 13

When astronomers look at distant galaxies, what sort of motion do they see?

A) The galaxies are all spinning rapidly.
B) The galaxies are all moving rapidly toward us.
C) The galaxies are all moving rapidly away from us.
D) Galaxies are orbiting a single point in the Universe.
E) Galaxies in half of the sky are moving away from us. Those in the other half are approaching.

Question 14

How do astronomers detect the movement of galaxies?

A) the shift in spectral lines of the galaxies
B) the steady dimming of the galaxy's light
C) the rapid brightening of the galaxy's light
D) the disappearance of the most distant galaxies as they move past the cosmic horizon

Question 15

What is meant by the redshift?

A) Distant galaxies appear red in color due to having older stars.
B) The temperature of distant galaxies is decreasing.
C) The spectral lines of the galaxies are shifted to redder wavelengths.
D) Distant galaxies appear red in color as their light passes through dust.
E) None of these choices is correct.

Question 16

What do astronomers infer from the motion of the distant galaxies?

A) The Universe is contracting.
B) The Universe is expanding.
C) The Universe is static.
D) The Universe is spinning.
E) None of these choices is correct.

Question 17

What evidence do astronomers have that the Universe is expanding?

A) There is a measurable redshift in the spectral lines of distant galaxies.
B) The disks of galaxies are getting smaller over time.
C) Distant galaxies are dispersing, pulled apart by the expansion of space.
D) Galaxies disappear when they pass the cosmic horizon.
E) Nearby clusters of galaxies are smaller than more distant ones.

Question 18

The light travel time distance to the cosmic horizon is about _________.

A) 14 × 10⁵ light-years
B) 14 × 10⁷ light-years
C) 14 × 10⁹ light-years
D) 14 × 10¹¹ light-years

Question 19

If the Universe had _________, that would resolve Olbers' paradox.

A) a finite age
B) an infinite extent
C) sources of new matter, like white holes
D) more mass than electromagnetic radiation
E) more electromagnetic radiation than mass

Question 20

Olbers paradox asks...

A) Why isn't the night sky bright as day?
B) Which is the simplest cosmological model?
C) If dark matter is dark, how can we ever see it?
D) How the Universe can be younger than some of the stars in it?

Question 21

The "light travel time distance" measures...

A) the distance light travels in one year.
B) how far the light from a galaxy would have traveled if the Universe was not expanding.
C) the amount of time the sunlight takes to reach Earth.
D) All of these choices are correct.

Question 22

The Big Bang refers to...

A) the creation of the Solar System.
B) the creation of the Moon.
C) the origin of the Universe.
D) the origin of the heavy elements in a supernova.
E) None of these choices is correct.

Question 23

The cosmic microwave background (CMB) radiation is...

A) light from distant stars.
B) radiation from pulsars.
C) light from gravitational lenses.
D) radiation from the birth of the Universe.
E) energy emitted by black holes at the centers of the nearby galaxies.

Question 24

The cosmic background radiation has a low temperature today because...

A) it is rich in heavy elements that absorb radiation very strongly.
B) the Universe has expanded, and expansion causes cooling.
C) it was created with a low temperature.
D) it has gotten so far from the Sun.
E) all the stars that were heating it have burned out.

Question 25

The ___________ is determined by the distance that ____ can travel in a time span equal to the age of the Universe.

A) cosmic horizon; light
B) recession velocity; galaxies
C) event horizon; light
D) cosmological constant; neutrinos

Question 26

Recent measurements of the variations of the cosmic background radiation suggest that the curvature of the Universe is ______.

A) positive
B) negative
C) flat (i.e., no curvature)

Question 27

If the universe had _________, that would resolve Olbers' paradox.

A) an infinite age
B) an edge in space
C) sources of new matter, like white holes
D) more mass than electromagnetic radiation
E) more electromagnetic radiation than mass

Question 28

What is the cosmic horizon?

A) the place where the Big Bang occurred
B) the average distance between galaxies
C) the distance beyond which astronomical objects are invisible because their light has not yet reached us
D) the diameter of the Universe

Question 29

If the Universe is infinitely large, infinitely old, and expanding, the night sky should be bright. But in fact, it is not. What do we call this?

A) the Cosmological Principle
B) Olbers' paradox
C) the Hubble Distance law
D) the Neutrino Discrepancy
E) Grand Unified Theory

Question 30

Astronomers have found the cosmic microwave background (CMB) radiation. What is the nature of this radiation?

A) It is a bright, uniform X-ray glow.
B) It is a faint, uniform radio signal.
C) It is a faint, uniform X-ray glow.
D) It is a weak and very patchy glow at visible wavelengths.
E) It is a weak background of cosmic neutrinos.

Question 31

About what temperature does the CMB have at this time?

A) 30 million K
B) 3 trillion K
C) 3 billion K
D) 3,000 K
E) 3 K

Question 32

Why is the CMB so cool now?

A) The expansion of the Universe has stretched the radiation to longer wavelengths.
B) Clouds of dust have blocked or scattered most of the radiation.
C) Energy from the CMB was transformed into dark energy.
D) The radiation's energy drives the expansion of the Universe.

Question 33

What is the cosmic microwave background?

A) radio noise from Seyfert galaxies
B) radiation from hot gas in intergalactic space
C) radiation from the first stars formed when the Universe was young
D) radiation released when neutral atoms formed in the young Universe

Question 34

Which of the following is evidence that the early Universe was hot and dense?

A) intense X-ray emission from gas in galaxy clusters
B) The ratio of helium to hydrogen is approximately the same in all old stars.
C) the cosmic microwave background
D) the intense luminosity of quasars

Question 35

Which sequence of events is in the correct chronological order?

A) Protons form, helium is produced, protons and electrons recombine into atoms, quarks form.
B) Protons form, quarks form, protons and electrons recombine into atoms, helium is produced.
C) Quarks form, protons form, protons and electrons recombine into atoms, helium is produced.
D) Quarks form, protons form, helium is produced, protons and electrons recombine into atoms.

Question 36

When the Universe was young, it was...

A) bigger and colder.
B) smaller and hotter.
C) bigger and more dense.
D) bigger and hotter.
E) smaller and less dense.

Question 37

According to the Big Bang model, most of the _________ in the Universe were formed ________.

A) hydrogen and helium; during the first 3 minutes
B) hydrogen and helium; during supernova explosions
C) hydrogen and helium; in the interior of massive stars
D) heavy elements; during the first 3 minutes

Question 38

According to the Big Bang model, in the earlier state of the Universe gamma rays converted into ________.

A) pairs of matter and antimatter
B) pairs of protons and neutrons
C) hydrogen and helium
D) X-rays

Question 39

When the Universe was young, it was...

A) bigger and colder.
B) smaller and colder.
C) denser.
D) bigger and hotter.
E) smaller and less dense.

Question 40

Where did helium come from the early Universe?

A) The early Universe was so hot and dense that fusion of protons (hydrogen) into helium could occur.
B) Helium was formed in the cores of stars formed in the early Universe.
C) Photons bombarded hydrogen atoms and broke them up into helium atoms.
D) Helium was not formed in the early Universe, because only neutrons were present.

Question 41

What is a quark?

A) a remote active galaxy
B) kind of subatomic particle that protons and neutrons are composed of
C) a burst of radiation seen near black holes
D) a very short wavelength radiation emitted by active galaxies
E) None of these choices is correct.

Question 42

The Big Bang theory can explain

A) the expansion of the Universe
B) the cosmic microwave background radiation
C) the relative abundance of helium in the Universe
D) All of these choices are correct.

Question 43

In a positively-curved Universe (the surface of Earth has positive curvature), the angles of a triangle add up to...

A) exactly 180 degrees.
B) more than 180 degrees.
C) less than 180 degrees.

Question 44

In a negatively-curved Universe (like the surface of a saddle), the angles of a triangle add up to...

A) exactly 180 degrees.
B) more than 180 degrees.
C) less than 180 degrees.

Question 45

The curvature of space can be measured by...

A) drawing triangles on the surface of Earth and adding up the angles.
B) by studying the redshift of light from distant galaxies.
C) by studying the ratio of helium and lithium produced in the Big Bang to hydrogen.
D) studying the fluctuations in the cosmic microwave background radiation.

Question 46

Which of the following are predictions of inflation theories?

A) The Universe expanded rapidly over a short period of time.
B) The smaller initial size of the Universe allowed thorough mixing.
C) The cosmic microwave background must be uniform.
D) All of these choices are correct.

Question 47

Within cosmology, inflation is the idea that...

A) the force of gravity suddenly grew stronger in the distant past.
B) the Universe increased dramatically in size in an extremely brief period of time.
C) the number of galaxies we see at large distances is greater than the number we can see near us.
D) the diameters of distant galaxies are much greater than those of galaxies near us.

Question 48

Which Big Bang "puzzles" does the inflationary model resolve?

A) The energy of expansion is almost exactly equal to the collective gravitational force between galaxies.
B) The Universe is all ordinary matter with almost no antimatter.
C) The cosmic background radiation is smooth, but the distribution of matter in the Universe is lumpy.
D) All of these choices are correct.

Question 49

In a GUT (Grand Unified Theory), what is "unified"?

A) matter and energy
B) the fundamental forces
C) galaxies
D) subatomic particles
E) all of space

Question 50

The discovery that the Universe is expanding faster today than in the past was possible because of observations of...

A) Cepheid variable stars.
B) Type Ia (white dwarf) supernovae.
C) Type II (core collapse) supernovae.
D) galaxy rotation curves.

Question 51

The observational evidence in favor of the existence of dark energy involves using _________ to calculate _________.

A) the method of inflation; the distance to distant galaxies
B) the method of standard candles; the distance to distant galaxies
C) Hubble's law; the distance to distant galaxies
D) Hubble's law; the age of the Universe

Question 52

If the density of the Universe is less than the critical density, then...

A) the Universe will expand forever.
B) the Universal expansion will eventually stop sometime in the future.
C) the Universe will eventually stop expanding, and then begin to collapse until it ends in a Big Crunch
D) the Universe will not change because its evolution does not depend on the critical density.

Question 53

Astronomers have found that the expansion of the Universe is _________.

A) speeding up
B) slowing down
C) changing randomly
D) constant

Question 54

Dark energy appears to make up approximately ______ of the Universe.

A) 90%
B) 70%
C) 10%
D) 1%

Question 55

If the density of the Universe is ___ than the critical density, then the Universe will ________.

A) larger; expand forever
B) larger; eventually collapse in a "Big Crunch"
C) less; not change in size
D) less; eventually collapse in a "Big Crunch"

Question 56

The critical density for the Universe is about

A) equal to six hydrogen atoms per cubic meter.
B) the same as the density of Earth.
C) the same as the density of the Sun.
D) equal to 6,000 hydrogen atoms per cubic meter.
E) equal to 600,000 hydrogen atoms per cubic meter.

Question 57

Within cosmology, the critical density is...

A) the density of the Universe.
B) the density of the most massive black hole in the Universe.
C) the density that determines whether the Universe expands forever or recollapses.
D) the density of Universes in the multiverse.
E) None of these choices is correct.

Question 58

If its density is less than the critical density, then a universe ________.

A) expands forever
B) will re-collapse
C) contains only antimatter
D) never expands

Question 59

Astronomers have found evidence that the expansion of the Universe is accelerating. Such acceleration...

A) is evidence for a cosmic repulsion related to the cosmological constant of relativity theory.
B) is deduced because nearby galaxies are receding faster than expected from the Hubble law.
C) is deduced because distant galaxies are receding faster than expected from the Hubble law.
D) was predicted by the Big Bang model in cosmology.

Question 60

Astronomers have found evidence that the expansion of the Universe is accelerating. Such acceleration...

A) is deduced because nearby galaxies are receding faster than expected from the Hubble law.
B) is deduced because distant galaxies are receding more slowly than expected from the Hubble law.
C) is deduced because distant galaxies are receding faster than expected from the Hubble law.
D) was predicted by the Big Bang model in cosmology.

Question 61

How does the observed density of luminous matter (stars and galaxies) in the Universe compare with the critical density?

A) The density of luminous matter is far smaller than the critical density.
B) Amazingly, the density of stars and galaxies exactly equals the critical density.
C) The density of stars and galaxies is vastly bigger than the critical density.

Question 62

Observations of the tiny irregularities in the cosmic microwave background support the idea that the Universe...

A) will collapse in the distant future.
B) contains no dark matter.
C) will continue to expand forever.
D) is composed primarily of neutrinos.
E) is composed primarily of matter, rather than antimatter.

Question 63

Observations of the tiny irregularities in the cosmic microwave background support the idea that the Universe...

A) must contain about 5 times more dark matter than regular matter.
B) does not contain dark energy.
C) must contain hidden pockets of antimatter.
D) must be one of many "island universes".

Question 64

Olbers' paradoxasks...

A) Why isn't the night sky bright as day?
B) Which is the simplest cosmological model?
C) If dark matter is dark, how can we ever see it?
D) How the Universe can be younger than some of the stars in it?

Question 65

One limit on the age of the Universe is that it must be older than the oldest stars.

Question 66

We are at the center of the Universe, and hence, everything is expanding away from us.

Question 67

An astronomer claims to have measured the spectrum of a nearby galaxy and finds that the spectral lines are slightly blueshifted. This result is unreliable because it violates Hubble's law.

Question 68

It is difficult to use light from distant galaxies to compute the true physical distance to those galaxies today because the Universe has expanded since it was emitted.

Question 69

As space expands, everything in it is also getting bigger.

Question 70

The cosmic horizon is the distance beyond which there are no more stars or galaxies.

Question 71

The cosmic microwave background radiation argues in favor of the Big Bang model.

Question 72

At the time of recombination, all of the Universe was about as hot as the core of the Sun.

Question 73

The Big Bang produced all the observed helium that we see today.

Question 74

Dark energy can exist in completely empty space.

Question 75

Dark energy is speeding up the expansion of the Universe.

Question 76

All the ordinary matter, both luminous and nonluminous, makes up less than 5% of the Universe.

Question 77

If the density of the Universe is greater than the critical density, then the expansion of the Universe will continue indefinitely.

Question 78

The inflation theories of the Universe allow for the existence of other unobservable Universes that may be expanding or collapsing.