Deck 25: Cosmology: The Origin and Evolution of the Universe

Question 1

In which of the following areas of scientific study will we never be able to follow the scientific method in repeating the observations of several different "samples" in order to verify the generality of the conclusions?

A)biology, the study of living things
B)cosmology, the study of the structure of our universe
C)archaeology, the study of the past evolution of living creatures
D)geology, the study of Earth as a planet

Answer 1

B

Question 2

The question asked in Olber's paradox of cosmology is:

A)"Why is the sky dark at night?"
B)"How old is the universe?"
C)"What is beyond the edge of the universe?"
D)"Where did the universe come from?"

Answer 2

A

Question 3

Newton reached the conclusion that the universe must consist of an infinite expanse of stars because:

A)he was unable to detect the movement of stars around a common center, which his theory required for stability against collapse in a finite universe.
B)he reasoned that a finite number of stars would eventually fall together under their mutual gravity.
C)of his religious conviction that the creator would create nothing less than an infinite universe.
D)he and his colleagues had observed the uniform distribution of stars all over the sky.

Answer 3

B

Question 4

How does Einstein's view of time compare with Newton's view?

A)They are virtually the same.
B)In Newton's model the passage of time is different near a large mass than when away from a large mass. In Einstein's model this is untrue.
C)In Einstein's model the passage of time is different near a large mass than when away from a large mass. In Newton's model this is untrue.
D)In Einstein's model of time it is possible to have an effect appear before its cause. In Newton's view this never happens.

Question 5

In Newton's model of an infinite universe with stars distributed smoothly throughout, an individual star would feel:

A)a preponderance of force pulling it toward the center of the universe.
B)a preponderance of force pushing it away from the center of the universe.
C)equal forces pulling in every direction, resulting in no net force.
D)forces that would vary greatly from one part of the universe to another.

Question 6

What was Einstein's cosmological constant, denoted by the Greek letter lambda, intended to represent?

A)the rate at which clocks run differently in gravitational fields
B)a pressure that tends to make the universe expand
C)the degree of curvature of space around massive objects
D)the age of the universe

Question 7

The expansion of the universe means that:

A)as time goes by, galaxies move away from each other through empty space.
B)as time goes by, space itself expands carrying the galaxies along with it.
C)each object in the universe expands its size.
D)the light from distant galaxies is Doppler shifted as the galaxies move away from us.

Question 8

When we view a quasar with a redshift z, this means the wavelengths of light emitted from the quasar have been shifted by z = Δλ \ λ₀. This wavelength shift is:

A)a Doppler shift.
B)a gravitational redshift.
C)a cosmological redshift.
D)all three of the above since they are one and the same thing.

Question 9

Which one of the following statements represents a correct description of the expansion of the universe?

A)Space is a vacuum, but the vacuum has real properties. As galaxies (or superclusters of galaxies) hurtle outward, the expansion is gradually slowing down by the resistance of space to the passage of the galaxies.
B)Space is static, but exerts an outward pressure on the galaxies in it. This pressure is accelerating the galaxies (or superclusters of galaxies) outward through space and away from each other.
C)Space has a separate existence, with the galaxies inside it. As space expands, the galaxies (or superclusters of galaxies) are carried along by the expansion.
D)Space is a vacuum, which is really nothing at all. The galaxies (or superclusters of galaxies) are hurtling outward through this nothingness.

Question 10

Where in the universe does the "general" expansion occur?

A)only within individual galaxies, while the space between them and between clusters of galaxies remains static
B)everywhere in the universe, including our local space upon Earth, the solar system, our galaxy, and the space between galaxies
C)only in galaxy-sized and larger structures, such as clusters of galaxies and the voids between them
D)only in the space that separates clusters of galaxies

Question 11

What is the lookback time (i.e., how long ago did the light leave its source) for an object with a redshift z = 0.05, assuming that the Hubble constant is 22.4 km/s/Mly? (Assume nonrelativistic speed for this object.)

A)335 billion years
B)670 thousand years
C)670 million years
D)670 billion years

Question 12

An object has a lookback time of 1 billion years. Assuming it is nonrelativistic, and that the Hubble constant is 22.4 km/s/Mly, what is its velocity?

A)6400 km/s
B)22,400 km/s
C)44,800 km/s
D)129,000 km/s

Question 13

An object has a lookback time of 1 billion years. Assuming it is nonrelativistic, and that the Hubble constant is 22.4 km/s/Mly, what is its cosmological redshift?

A)0.074
B)0.126
C)0.546
D)1.89

Question 14

In our description of the universe, what does the word "homogeneous" mean?

A)Every region is the same as every other region.
B)The universe looks the same in every direction.
C)The universe is expanding uniformly at every point.
D)Every galaxy is moving away from every other galaxy.

Question 15

In our description of the universe, what does the word "isotropic" mean?

A)Every region is the same as every other region.
B)The universe looks the same in every direction.
C)The universe is expanding uniformly at every point.
D)Every galaxy is moving away from every other galaxy.

Question 16

What does z = 0 mean?

A)zero time-that is, the time at which the cosmic singularity occurred
B)zero acceleration-that is, constant velocity
C)zero velocity-that is, only objects at rest with respect to Earth have z = 0
D)zero expansion-that is, no cosmological redshift

Question 17

Is there an advantage in using redshift z to describe the distances to faraway galaxies?

A) No. Because z is a known function of v (which function depends on whether the situation is relativistic or nonrelativistic) and v = H0d, there is no real advantage to using z rather than d.
B) No. Not all objects at the same d have the same z, so using z is actually a disadvantage.
C) Yes, z can be determined rather easily from spectra, whereas H0 is rather difficult to determine. So there is a real advantage in using z rather than d.
D) No. Because one cannot always be sure whether to use relativistic or nonrelativistic equations for z, z is somewhat ambiguous while d is unambiguous.

Question 18

An object has a lookback time of 1 billion years. Assuming it is nonrelativistic, and that the Hubble constant is 22.4 km/s/Mly, what would be the measured value of its H_" $\alpha$ (656.3-nm) line?

A)621 nm
B)656.3 nm
C)705 nm
D)1209 nm

Question 19

Astronomers currently estimate the age of the universe to be:

A)about 4.5 billion years old.
B)about 13.7 billion years old.
C)almost 1000 billion years old.
D)infinitely old.

Question 20

For any object moving uniformly, velocity = distance/time. If so, in the Hubble relationship for the expansion of the universe, V = H₀d, what is the significance of the constant 1/H₀?

A) It is the inverse of the velocity that the object would have at a standard distance of 10 pc.
B) It represents the average spacing between objects in the universe at the present time.
C) It is merely a constant of proportionality, to allow for the different units of V and d.
D) It represents the time since the expansion began, or the age of the universe, assuming the expansion has been uniform.

Question 21

If the Hubble constant is found to be 25 km/s/Mly, what would then be an upper estimate for the age of the universe?

A)1.2 billion years or 1.2 × 10⁹ years
B)12 billion years or 1.2 × 10¹⁰ years
C)12 million years or 1.2 × 10⁷ years
D)380 billion years or 3.8 × 10¹¹ years

Question 22

The farthest object we have seen (in 2011) has a redshift z of about 7.09, which corresponds to a recessional velocity v = 0.970c. What is the light travel time for this object as a percentage of the estimated age of the universe, 13.4 billion years?

A)55.9%
B)64.0%
C)94.0%
D)97.0%

Question 23

A few decades ago many astronomers used a value 42 km/s/Mpc for the Hubble constant. What was the age of the universe based on this value?

A)11.2 billion years
B)13.4 billion years
C)19.6 billion years
D)23.3 billion years

Question 24

If the uncertainty in the Hubble constant H₀ = 73 km/s/Mpc is 10%, leading to values of between 65.7 km/s/Mpc and 80.3 km/s/Mpc, what is the corresponding range in the estimated age of the universe?

A)1.7 billion years, from 12.2 to 14.9 billion years
B)2.8 billion years, from 12.8 to 15.6 billion years
C)There is insufficient information to calculate this uncertainty from the given numbers.
D)1.4 billion years, from 12.7 to 13.9 billion years

Question 25

If the Hubble constant is 73 km/s/Mpc then the age of the universe is 13.4 billion years, assuming a uniform expansion. Suppose it were discovered that the Hubble constant is actually larger than 73 km/s/Mpc. What effect would this have on the calculated age of the universe?

A)Without another factor, the average mass density of the universe, the age of the universe cannot be estimated from this information.
B)It would decrease the calculated age of the universe.
C)Because the Hubble constant simply relates galaxy motion to its distance from our galaxy, it has no connection with the age of the universe.
D)It would increase the calculated age of the universe.

Question 26

What major problem would arise if the value of the Hubble constant turned out to be 100 km/s/Mpc?

A)Some galaxies would be farther away than the edge of the universe.
B)Galaxies would have had to have traveled faster than our observations indicate.
C)Galaxies would be traveling too fast for the universe to be gravitationally bound.
D)The age of the universe would be less than the ages of some of the stars in it.

Question 27

Suppose it is discovered that the Hubble constant is half the value we have been using. (The redshifts have all been measured correctly.) What would this mean for the calculated distances to distant galaxies?

A)The distance calculations would be unaffected.
B)All calculated distances would be halved.
C)All calculated distances would be doubled.
D)All calculated distances would more than double.

Question 28

If the elliptical galaxy in Hydra, shown at the bottom of Figure 23-16 (Universe, 11th ed.), were to be at a distance of 3 billion ly, what would be a lower limit to the age of the universe? (Be careful with units.)

A)0.47 billion years
B)4.5 billion years
C)15 million years
D)15 billion years

Question 29

What is the z value for an object on our cosmic light horizon?

A)0
B)0.137
C)1
D)infinity

Question 30

What was it that caused the apparent expansion of the universe?

A)our point of view, the expansion being a projection effect resulting from Earth's motion in the galaxy
B)the centrifugal force upon all matter in the universe, caused by motion around its center
C)a universal repulsive force, stronger than the gravitational attraction between matter in the universe
D)No cause has yet been found, but the expansion started suddenly and has continued to this time.

Question 31

The first 10^-43 seconds of the age of the universe, during which time matter was so compressed that all known science fails us, is called the:

A)inflationary epoch.
B)event horizon.
C)Hubble time.
D)Planck time.

Question 32

Within which time frame from the initial Big Bang is it felt that the present laws of physics completely fail us, because time and space as we know them did not exist?

A)t = 0 to 1 s, during which time photons interchanged freely with electron-positron pairs
B)t = 0 to 10^-35 s, after which the strong nuclear force "froze out" of the universe
C)t = 0 to 10^-43 s, the Planck time, after which gravity "froze out" of the universe
D)t = 0 to 10⁶ years, over which radiation dominated the universe

Question 33

We see distant objects as they were at the time that light left them. Assuming a Hubble constant, H₀, of 73 km/s/Mpc, what would be the age of the universe?

A)13.7 million years
B)∞ (infinity)
C)13.7 billion years
D)47.4 billion years

Question 34

The discovery that the Sun and similar stars consist of about 25% helium posed a dilemma: There was too much helium in the universe to be accounted for by nucleosynthesis in stars in the contemporary cosmological models. How was this dilemma resolved?

A)The universe was found to be older than originally thought, thus allowing more time for stars to produce helium.
B)New helium-producing reactions were discovered in addition to the usual hydrogen-to-helium reaction.
C)It was discovered that earlier generations of stars were larger and hotter than previously thought and thus able to produce more helium.
D)The early universe was found to be hot and dense enough to produce helium from hydrogen, even before the first stars were formed.

Question 35

The Sun presently consists of about 25% helium. Where did this helium come from?

A)All of it was formed by hydrogen fusion in the Sun's core.
B)Some was formed by hydrogen fusion in the Sun's core, but most of it came from hydrogen fusion in previous generations of stars.
C)Virtually all of it was formed in supernova eruptions and then scattered through space, where it formed part of the gas and dust from which the Sun was formed.
D)A significant part was formed in the early universe before any stars formed.

Question 36

The 2.7-K cosmic microwave background radiation comes from:

A)the combined radiation of all the distant galaxies.
B)clouds of hot gases in clusters of galaxies.
C)radioactivity within Earth.
D)the decoupling of radiation and matter in the early universe.

Question 37

The cosmic background radiation is the:

A)electromagnetic remnants of the explosion in which the universe was born.
B)radio noise caused by high energy atomic nuclei known as cosmic rays, moving through magnetic fields in space.
C)result of the radioactive decay of heavy, unstable elements produced in supernova explosions.
D)faint glow along the ecliptic, caused by sunlight scattering from dust particles in the planetary system.

Question 38

From what direction do we receive the cosmic microwave background?

A)from Sagittarius, in the direction of the galactic center
B)from the Great Attractor
C)from Leo, so that direction must represent the center of the Big Bang
D)from all directions, almost uniformly

Question 39

I thought that the Big Bang was hot! If the cosmic microwave background radiation is the radiation left over from the Big Bang, why then is it only 3 K?

A)The Big Bang itself was hot, but the temperature decreased as the universe expanded, and the temperature now is 3 K.
B)It is not from the Big Bang itself-it is from cold, intergalactic hydrogen clouds that are left over from the Big Bang.
C)The Big Bang itself was hot, but by the time the universe became transparent the temperature had already decreased to 3 K.
D)The Big Bang was not hot-its temperature was the same as we observe it now from the cosmic background radiation.

Question 40

Compared to the average density of matter in the present universe, the equivalent "mass density" of radiation, using Einstein's relation E = mc² for the photons, is:

A)much greater, leading to a radiation-dominated universe.
B)almost nonexistent, because there is very little radiation left in the universe at the present time.
C)equal, because these parameters remain balanced throughout the evolution of the universe as a consequence of the equipartition of energy.
D)much less, leading to a matter-dominated universe.

Question 41

At present, the energy density of matter greatly exceeds that of radiation. But in the early universe, radiation energy was dominant. Why was this?

A)Dark matter had not yet formed to add to the matter energy density.
B)The radiation temperature was high enough to prevent the transformation of radiation into matter; photon Y matter + antimatter.
C)Radiation was at a much greater temperature (and energy) and density than now.
D)Large numbers of antiparticles existed and combined with matter particles to form photons.

Question 42

At about what time after the Big Bang did the universe pass through the transition from a radiation-dominated to a matter-dominated universe?

A)about 15 billion years, as stars began to form
B)24,000 years
C)380,000 years
D)at the Planck time, 10^-43 s

Question 43

The ionization energy of a hydrogen atom, that is the energy required to remove the electron from the atom completely, is 13.6 electron volts. Suppose it were 25 electron volts instead. What difference would this make to cosmology?

A)None. Individual atoms are much too small to have any effect on the evolution of the universe.
B)The cosmic microwave background radiation would be hotter than 2.7 kelvins.
C)The cosmic microwave background radiation would be cooler than 2.7 kelvins.
D)There would be no cosmic microwave background radiation.

Question 44

Suppose the ionization energy of hydrogen were larger than 13.6 eV and the decoupling of radiation and matter had occurred earlier, say at z = 2000. What would the temperature have been at that time?

A)2500 K
B)3000 K
C)3500 K
D)5500 K

Question 45

The conditions in the early universe, when the universe suddenly became transparent to radiation, in terms of age t, peak background wavelength λ, and equivalent temperature T, were:

A)t = 3 minutes, λ = 0.3 μm, near UV, and T = 10⁷ K.
B)t = 380,000 years, λ = 1 μm, infrared, and T = 3000 K.
C)t = 3 × 10¹¹ years, λ = 1 mm, microwaves, and T = 3 K.
D)The universe was never dominated by radiation, because matter has always dominated by generating the gravitational field into which the universe has expanded.

Question 46

As we look at more distant regions of space, we see those regions as they existed at earlier times, but our farthest views are blocked by a "wall"-beyond which the universe is opaque. What event occurred at the time marked by this wall?

A)Electrons and protons combined to form neutral hydrogen atoms, making the universe transparent for the first time.
B)Quarks combined to form neutrons and protons, removing $\gamma$ -ray absorbers for the first time.
C)Gravity froze out as a separate force.
D)Electrons and protons combined to form helium atoms, removing major absorbers of electromagnetic radiation from the universe for the first time.

Question 47

Figure 25-13 of Universe, 11th ed., shows temperature variations in the cosmic microwave background. Dark areas in the image correspond to regions where the photons were gravitationally redshifted when they left the early universe. Suppose we point a telescope at one of these regions now. What would we expect to see?

A)nothing, because the early universe no longer exists
B)a fuzzy ball, because the primordial fireball is as far back as we can see
C)a red glow, because of the gravitational redshift
D)some structure, perhaps a cluster of galaxies, because such regions indicate clumps of larger density in the early universe

Question 48

When the universe was about 24,000 years old, the radiation density had decreased to the point where it was equal to the matter density, yet it was only many years later that atoms formed. What happened to make possible the formation of atoms?

A)The average photon energy decreased until it could no longer ionize hydrogen.
B)Radiation pressure decreased until it was equal to the inward pressure due to gravity.
C)The temperature reached the point where the reaction ¹H $\rightarrow$ ⁴He could proceed.
D)Neutrons decayed to produce protons and electrons, the building blocks of atoms.

Question 49

What condition is necessary for the universe to be unbounded (infinite in extent)?

A)The density of the universe must be equal to or less than some critical value.
B)The density of the universe must be equal to or greater than some critical value.
C)The universe must have no mass in it.
D)The density of the universe must be exactly equal to some critical value.

Question 50

What will happen if the universe is unbounded?

A)The universe will expand forever.
B)The universe will expand to some maximum size and then fragment into mini-universes.
C)The universe will reach a maximum size and stay there, like a balloon that has been inflated.
D)The universe will eventually fall back in on itself, heading toward a recollapse.

Question 51

What will happen if the universe is bounded?

A)The universe will expand to some maximum size and then fragment into mini-universes.
B)The universe will eventually fall back in on itself, heading toward a recollapse.
C)The universe will reach a maximum size and stay there, like a balloon that has been inflated.
D)The universe will expand forever.

Question 52

In cosmology, to what does the phrase "critical density" refer?

A)the density of the universe above which matter is ionized and the universe is opaque
B)the density of the universe above which the universe is bounded and below which it is unbounded
C)the density of the universe below which the universe will stop expanding
D)the density of the universe below which the universe is bounded and above which it is unbounded

Question 53

How does the measured mass density of matter in the universe, including the hypothesized dark matter, compare to the critical density required to just close the universe?

A)The measured density is about 5 times the critical density.
B)The measured density is equal to the critical density to within the measurement uncertainty.
C)The measured density is less than 0.1 of the critical density.
D)The measured density is between 0.2 and 0.4 of the critical density.

Question 54

If space has a hyperbolic geometry (unbounded universe), what will happen to two initially parallel flashlight beams as they traverse billions of light years of space?

A)They will remain parallel.
B)They will gradually diverge (move apart) to a maximum separation, and then gradually converge and cross.
C)They will gradually converge (move together) and eventually cross.
D)They will gradually diverge (move apart).

Question 55

Measurement of structure in the cosmic microwave background radiation has recently indicated that we live in a flat universe between a closed and an open universe, and yet the measured density of detected matter and radiation is only 20% to 40% of the critical density required for a flat universe. In what form is the other 60% to 80% of the "matter" likely to be?

A)antimatter, which generates a negative gravitational effect and emits radiation only if it meets matter and is annihilated
B)neutrinos, which have very little rest mass and are very difficult to detect, but are very abundant
C)large numbers of small primordial black holes, whose gravitational effects are spread throughout the universe and that emit no radiation
D)dark energy, emitting no radiation and generating no detectable gravitational effects

Question 56

Einstein introduced a "cosmological constant" into his formulation of the structure of the universe on the basis of the general theory of relativity. How did he envision that this cosmological constant would manifest itself?

A)as antimatter that, by annihilating with real matter, would translate matter into energy, thereby maintaining a constant mass density in an condensing universe
B)as many "white holes" that would contribute matter to an expanding universe to maintain constant density, as required by the cosmological principle-a continuous creation universe
C)as a form of energy that, on its own, would make the universe expand-a form of antigravity
D)as an extra "gravity" that would hold the universe against continuous expansion

Question 57

The future of our universe-continuous expansion or eventual contraction-can be determined by observing the rate at which cosmological expansion is changing because of gravitational attraction between masses in the universe. How would this effect of deceleration be measured in terms of the Hubble relationship between speed of recession (graphed vertically) and distance (graphed horizontally)?

A)The straight line will become slightly curved and steeper at the largest distances.
B)The straight line will be found to be slightly curved and steeper at the shortest distances, but otherwise it will be straight.
C)The straight line will become slightly curved and less steep at the largest distances.
D)The straight-line slope will become zero at some distance and change to the opposite slope beyond this distance.

Question 58

It is not yet known whether we live in an unbounded universe that will expand forever or in a bounded universe that will eventually recollapse. How are astronomers trying to settle this question?

A)by accurate measurement of the speed of a galaxy of known distance at two different times, to measure the deceleration directly
B)by measuring the curvature of space by tracing photon paths to Earth from distant galaxies
C)by determining how much galaxy speeds depart from a straight-line Hubble relationship, v = H₀ d, at large distances
D)by careful observations of the size of the irregularities in the cosmic microwave background radiation

Question 59

If there is no dark energy, what is the future of the universe? (See Figure 25-18 of Universe, 11th ed.)

A)The future of the universe is not related to the geometry of space.
B)It will expand forever, not stopping even after infinite time, regardless of how much matter is in the universe.
C)It will expand to a maximum size and then recollapse.
D)It will barely expand forever, reaching zero expansion speed after infinite time.

Question 60

If there is dark energy in the universe with a positive energy density, what is the future of the universe? (See Figure 25-18 of Universe, 11th ed.(in the text))

A)It will expand forever at a rate that depends upon how much matter there is in the universe.
B)It will expand forever at an accelerating rate, regardless of how much matter there is in the universe.
C)The future of the universe is not related to the geometry of space.
D)It will expand to a maximum size and then recollapse.

Question 61

In which of the following universe scenarios will the present universe recollapse at some time in the future?

A)a Newtonian universe
B)a marginally bounded universe
C)an unbounded universe
D)a bounded universe

Question 62

If the universal expansion is accelerating, how does this affect the age of the universe derived from the Hubble law?

A)Acceleration has no effect on the derived age.
B)The derived age is higher than if the expansion is constant.
C)It can either increase of decrease the derived age, depending on the density of the universe and the resulting curvature of space.
D)The derived age is lower than if the expansion is constant.

Question 63

If, as we now believe, the rate of expansion of the universe was slower in the past than at present, then in the past the value of the Hubble ratio, H = v/d, was: (See Figure 25-16 of Universe, 11th ed.)
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A)negative.
B)its present value, H₀.
C)smaller than its present value.
D)larger than its present value.

Question 64

How is it that we can detect evidence of sound waves in the early universe?

A)The energy-rich environment of the early universe gave these sound waves so much energy that, unlike ordinary sound waves, they have been able to travel through the vacuum of space.
B)Space is not a complete vacuum. The tenuous material that fills all of space has been enough to sustain these sound waves.
C)What we observe is not the sound waves themselves but rather the spectrum of light emitted from the compressions and rarefactions of the sound waves.
D)What we observe is not the sound waves themselves but the gravitational lensing caused by the increased mass density in the compressions of the sound waves.

Question 65

Studying the pattern of temperature variations in the early universe (see Figure 25-13 of Universe, 11th ed.) tells us something about the sound waves existing at that time. This, in turn, has given us information about all of the following EXCEPT the:
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A)average densities of matter and dark energy.
B)average value of the Hubble constant at that time.
C)age of the universe at that time.
D)nature of dark energy.

Question 66

The density parameter Ω₀ measures the total mass-energy density in the universe from all sources as a function of the critical density. How much of this is from ordinary atomic matter and how much from dark matter?

A)About 5% is from ordinary matter and another 26% from dark matter.
B)About 24% is from ordinary matter and the remaining 96% is from dark matter.
C)About 50% is contributed by each of these sources.
D)About 96% is from atomic matter and the remaining 4% is from dark matter.

Question 67

What value for the Hubble constant is obtained from the observations of the ESA Planck satellite?

A)52 km/s/Mpc
B)68 km/s/Mpc
C)73 km/s/Mpc
D)84 km/s/Mpc

Question 68

By what factor has the universe expanded since the time of recombination?

A)10
B)10²
C)10³
D)10⁶