Deck 19: Cosmology

Question 1

The cosmological redshift in the light from distant galaxies is explained by which of these effects?

A) A photon's wavelength is a distance and is therefore lengthened by the general expansion of the universe, making the light appear reddened.
B) The light observed on Earth was Doppler-shifted to longer wavelengths by the motion of the objects (e.g., galaxies) away from Earth.
C) The light spreads out over larger areas as distance increases according to 1/(distance)², which causes the wavelength to increase in proportion to distance.
D) The light from more distant galaxies has traveled through the gravitational fields of more galaxies in getting to Earth and is therefore more gravitationally redshifted.

Answer 1

A photon's wavelength is a distance and is therefore lengthened by the general expansion of the universe, making the light appear reddened.

Question 2

Which scientist discovered that the equations he had derived predicted an expanding universe, then modified his equations to eliminate this expansion?

A) Albert Einstein
B) Isaac Newton
C) Stephen Hawking
D) Edwin Hubble

Answer 2

Albert Einstein

Question 3

When did Einstein originally introduce his theory of general relativity, including the cosmological constant?

A) in 1896, before the modern stellar spectral classification scheme was devised
B) in 1915, before the question of the nature of the Milky Way Galaxy had been resolved
C) in 1930, after Hubble had discovered evidence for the expanding universe
D) in 1968, after the discovery of the cosmic microwave background gave evidence of the Big Bang

Answer 3

in 1915, before the question of the nature of the Milky Way Galaxy had been resolved

Question 4

When Hubble did his early work on the expanding universe, he knew nothing about the cosmological redshift. He used the Doppler shift equations instead, but these gave him the correct answer. Why?

A) These two sets of equations (Doppler shift and cosmological redshift) are the same and always give the same result for all cases.
B) Hubble was using only ordinary galaxies. If he had used galaxies with AGNs, the equations would not have worked.
C) Hubble was fortunate enough to use only galaxies for which the gravitational redshift and the cosmological redshift nearly cancel, so the Doppler shift provided essentially the whole effect.
D) Hubble was using only relatively nearby galaxies for which the nonrelativistic cosmological redshift and the Doppler shift provide the same result.

Question 5

Why is the universe expanding?

A) The energy from all the stars is heating the universe, making it expand like a gas that is heated.
B) Spacetime itself is expanding, carrying the galaxies (or superclusters of galaxies) with it.
C) The universe is not expanding-it is the Galaxy that is getting smaller, making the universe seem bigger and bigger.
D) An infinitely dense clump of matter exploded, sending the galaxies (or superclusters of galaxies) hurtling out through space.

Question 6

Which of these BEST describes the universe as envisioned by Isaac Newton?

A) static and clumpy
B) expanding slowly and clumpy
C) expanding slowly and uniform
D) static and uniform

Question 7

Suppose an object is at rest and that it is emitting radiation. An observer at rest with respect to the object observes the radiation to be blueshifted from its original frequency. This blueshift can be caused by

A) the Doppler shift only.
B) the gravitational wavelength shift only.
C) the cosmological wavelength shift only.
D) either the gravitational or the cosmological wavelength shift

Question 8

Which of these statements is a correct description of the expansion of the universe?

A) Spacetime is something real, with galaxies inside it; as spacetime expands, the galaxies (or superclusters of galaxies) are carried along by the expansion.
B) 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.
C) Spacetime is static, but dark matter, which is concentrated in the outer part of the universe, pulls outward on the galaxies.
D) Space is a vacuum, which is really nothing at all; the galaxies (or superclusters of galaxies) are hurtling outward through this nothingness.

Question 9

Consider four different regimes of space in which distances between objects might be changing as a result of the general expansion of the universe: (1) distances between different parts of Earth; (2) distance between planets in the solar system; (3) distances between stars in the Milky Way; (4) distances between clusters of galaxies. In which of these regimes are the distances changing because of the universe's expansion?

A) 4, 3, 2, 1
B) 4
C) 4, 3, 2
D) 4, 3

Question 10

Einstein's general theory of relativity, as originally formulated without the cosmological constant, predicts a universe that

A) is static.
B) must expand.
C) must contract.
D) must either expand or contract.

Question 11

When astronomers view a distant quasar with highly redshifted emission lines in its spectrum, this wavelength shift is a

A) Doppler shift.
B) gravitational redshift.
C) cosmological redshift.
D) Doppler shift or a gravitational redshift or a cosmological redshift-they are one and the same thing.

Question 12

Why did Einstein introduce his cosmological constant into the original equations for general relativity?

A) The constant was necessary to make the solutions describe an expanding universe.
B) Experimental evidence at this time (before Hubble) suggested a static universe, and this constant was required to produce static solutions.
C) The constant represented the acceleration of gravity near Earth's surface, and it was necessary to make the nonrelativistic limit of the solutions compatible with Newton's results.
D) The constant represented the speed of light, and its inclusion was necessary to produce solutions that were compatible with the postulates of special relativity.

Question 13

What is the "cosmological redshift"?

A) stretching of the wavelengths of photons as they travel through expanding space
B) stretching of the wavelengths of photons by the Doppler shift because they are emitted by galaxies that are moving away from Earth
C) loss of energy from photons interacting with virtual particles in the vacuum, resulting in the wavelength of the photons gradually increasing as they travel toward Earth through space
D) stretching of the wavelengths of photons as they pass through absorbing matter in galaxies between Earth and the emitting galaxy

Question 14

The cosmological redshift of the light from very distant galaxies is caused by the

A) rotation of the universe around its center (faster at greater distances from Earth).
B) expansion of space, stretching the photon's wavelength while the photon is traveling toward Earth.
C) absorption of blue light by interstellar dust between Earth and the galaxy so that only the red wavelengths reach Earth.
D) Doppler shift, in which the photon's wavelength is stretched by the galaxy's motion through space, away from Earth, while the photon is being emitted.

Question 15

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

A) he and his colleagues had observed the uniform distribution of stars all over the sky.
B) 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.
C) of his religious conviction that the creator would create nothing less than an infinite universe.
D) he reasoned that if stars were not uniformly distributed everywhere, then denser portions of the universe would clump together under their own gravity.

Question 16

Which of these statements BEST describes the history of the cosmological constant?

A) Einstein introduced the constant to make the universe static, but many cosmologists now believe it makes the expansion of the universe accelerate.
B) Einstein introduced the constant to make the universe expand, and it is still necessary to cosmological theories today.
C) Einstein introduced the constant to make the universe static, but Hubble's discovery of the expanding universe proved that it the constant actually vanishes.
D) Einstein introduced the constant to make the universe expand, and it is now known that it has a much higher value today because the expansion is accelerating.

Question 17

The farther away a galaxy is, the more its light is redshifted, as observed from Earth. This relationship between redshift and distance is caused by

A) the Doppler shift of light leaving a moving object. More distant galaxies are moving faster through space, so their light is more strongly Doppler-shifted (redshifted).
B) energy losses. The universe does not really expand; photons simply lose energy (wavelength lengthens) as they travel. Photons from more distant galaxies have traveled farther and so are more redshifted.
C) the expansion of space itself, which stretches the wavelength of the photon. The longer the time the photon has traveled, the more space has expanded and therefore the more the photon has been redshifted.
D) the gravitational redshift. Photons leaving a more distant galaxy have traveled farther through the galaxy's gravitational field, so they have lost more energy and are more redshifted.

Question 18

The expansion of the universe takes place

A) only between objects separated by vacuum; as a result, human bodies do not expand, but the Earth-Moon system does.
B) between all objects, even between the atoms in human bodies, although the expansion of a person is too small to be measured reliably.
C) only over distances the size of a galaxy or larger; consequently, the Milky Way Galaxy expands, but the solar system does not.
D) primarily in the huge spaces between clusters of galaxies; "small" objects like galaxies or Earth do not expand.

Question 19

What causes the cosmological redshift of photons that reach Earth from distant galaxies?

A) The photons have traveled through space that has been expanding and their wavelengths have expanded with it, becoming redder.
B) The photons were emitted from the galaxies much earlier in time when the overall temperature of matter was much lower. Hence, the observed photons are redder the farther away from Earth they were produced.
C) The photons were emitted by objects that were moving rapidly away from Earth and thereby have been reddened by the Doppler effect.
D) The photons have moved from high-gravitational-field regions toward lower fields, thereby becoming reddened.

Question 20

What do cosmologists study?

A) formation, structure, and evolution of stars
B) origin, structure, and evolution of the solar system
C) formation, structure, and evolution of galaxies
D) large-scale structure and evolution of the universe

Question 21

Suppose that the expansion rate were slower in the past. Taking this fact into account when estimating the age of the universe from the presently accepted value of the Hubble constant, H₀ = 73.5 km/s/Mpc, yields

A) 13.4 billion years, as before.
B) a value less than 13.4 billion years.
C) a value greater than 13.4 billion years.
D) a value different from 13.4 billion years, but additional information is needed to determine whether it is larger or smaller.

Question 22

Suppose new experimental evidence were to point to a Hubble constant value of H₀ = 50 km/s/Mpc. A calculation of the age of the universe using this value would give

A) the same value now calculated, namely 13.4 billion years.
B) an age younger than 13.4 billion years.
C) an age older than 13.4 billion years.
D) a different value of the age, but more information is needed to estimate what it would be.

Question 23

Who developed the steady-state theory of the universe?

A) Dicke and Peebles
B) Alpher and Gamow
C) Hoyle, Bondi, and Gold
D) Penzias and Wilson

Question 24

Astronomer A claims that the Hubble constant is 84 km/s/Mpc, while astronomer B claims that it is 63 km/s/Mpc. The age of the universe calculated by astronomer A would be

A) 1.33 times the age calculated by astronomer B.
B) 2/3 of the age calculated by astronomer B.
C) 3/4 of the age calculated by astronomer B.
D) 1.25 times the age calculated by astronomer B.

Question 25

What would the age of the universe be if the Hubble constant, H₀, is 90 km/s/Mpc?

A) 17 billion years
B) 11 billion years
C) 15 billion years
D) 9 billion years

Question 26

An elliptical galaxy in Boötes (shown at the bottom of Figure 17-32 in the text) is at a distance of 1.6 billion ly and has an apparent recession speed of 39,000 km/s. What upper limit does this imply to the age of the universe? (Be careful with units.)

A) 0.47 billion years
B) 12 million years
C) 47 billion years
D) 12 billion years

Question 27

Because of the general expansion of space, all distant galaxies appear to be moving away from Earth, with speeds that increase with distance from the Milky Way Galaxy. What would an observer in one of these distant galaxies see?

A) same thing as seen from Earth: all galaxies moving away, with more distant galaxies moving faster
B) all galaxies moving nearer, with more distant galaxies moving faster
C) all galaxies moving away, with closer galaxies moving faster
D) all galaxies on one side of the sky moving nearer and all galaxies on the other side moving away, with more distant galaxies moving faster

Question 28

In order to estimate the age of the universe as 1/H₀ , astronomers must make a number of assumptions. Which of these is NOT one of the necessary assumptions?

A) The universe's expansion rate is the same in all directions.
B) The Milky Way Galaxy is the center of the universal expansion.
C) The value of H₀ is indeed constant.
D) The speed of the expansion has been constant through time.

Question 29

For any object moving uniformly, velocity = distance/time. So in the Hubble relationship for the expansion of the universe, v = H₀r, what is the significance of the constant 1/H₀?

A) This quantity represents the average spacing between objects in the universe at the present time.
B) This quantity represents the time since the expansion began, or the age of the universe.
C) This quantity is merely a constant of proportionality to allow for the different units in v and r.
D) This quantity is the inverse of the velocity that the object would have at a standard distance of 10 parsecs.

Question 30

When Hubble first calculated the recessional speeds of galaxies in the 1920s, he used

A) the Doppler shift relationship. This was an error, and the calculations had to be repeated using the cosmological redshift relationship.
B) the Doppler shift relationship. This was an error, and the calculations had to be repeated using the gravitational redshift relationship.
C) the Doppler shift relationship. This was correct because the nonrelativistic cosmological redshift relationship gives the same result.
D) the cosmological redshift relationship. This was an error, and the calculations had to be repeated using the Doppler shift relationship.

Question 31

According to Hubble's law, how old is the universe? (H₀ = Hubble constant)

A) v/H₀ (where v = recession velocity in km/s)
B) r/H₀ (where r = distance in Mpc)
C) H₀
D) 1/H₀

Question 32

Who first proposed that the observed motion of galaxies away from Earth implied the existence of a radio background pervading the universe?

A) Robert Dicke
B) George Gamow
C) Fred Hoyle
D) Edwin Hubble

Question 33

Suppose the expansion of the universe has been slowing since the Big Bang, and the value H₀ is the Hubble constant that is appropriate to the universe today. What would this say about the age of the universe?

A) The age should still be 1/H₀ = 13.4 billion years.
B) The age would be less than 13.4 billion years.
C) The age would be greater than 13.4 billion years.
D) It is not possible to answer the question based only on this information.

Question 34

If the Hubble constant is 75 km/s/Mpc, then the age of the universe is 13 billion years. Suppose it were discovered that the Hubble constant is actually larger than 75 km/s/Mpc. What effect would this fact have on the estimated age of the universe?

A) The estimated age could be increased or decreased, depending on the recession velocity of the galaxy being investigated.
B) The estimated age would be the same.
C) The estimated age would be decreased.
D) The estimated age would be increased.

Question 35

In cosmology, the constant that is intimately related to the present "age" of the universe is

A) the constant in Wien's law of radiation.
B) 1/G, the inverse of the universal gravitational constant.
C) the Planck time, 10^-43 s, in which space and time came into existence.
D) 1/H₀, the inverse of the Hubble constant of expansion.

Question 36

What would the age of the universe be if the Hubble constant, H₀, is 60 km/s/Mpc?

A) 15.0 billion years
B) 16.6 billion years
C) 60 billion years
D) 11.1 billion years

Question 37

Where is Earth?

A) at the exact center of an expanding universe, as shown by the universal expansion away from Earth in all directions
B) near the edge of an expanding universe, as shown by the microwave radiation coming to Earth from the edge
C) near but probably not right at the center of the universe, as shown by the fact that the edge is so far away from Earth
D) somewhere in an expanding universe but not in any special part of it

Question 38

Suppose H₀ = 71 km/s/Mpc. What is H₀ in m/s/ly?

A) 2.2 * 10^-3
B) 2.2 * 10^-2
C) 22
D) 2.2 * 10³

Question 39

Who first proposed that the observed motion of galaxies away from Earth originated as an expansion outward from an extremely dense state of matter at the beginning of the universe?

A) Edwin Hubble
B) George Gamow
C) Fred Hoyle
D) Georges Lemaître

Question 40

What is it that keeps localized regions of space, such as things on Earth, planetary systems, star clusters, and whole galaxies, from participating in the general expansion of the universe?

A) their locations in places where irregularities in the chaotic Big Bang explosion permitted matter to condense
B) mutual gravitational attraction between objects in these systems
C) centrifugal force produced by the motion of the regions around a massive central object (e.g., the Sun, a supermassive black hole, etc.)
D) powerful and all-pervading gravitational pull from the central supermassive black holes of galaxies that holds everything in the galaxies in place

Question 41

Good evidence for an original Big Bang that "created" this universe comes from

A) the rapid motions of some nearby stars, such as Barnard's Star.
B) a background "glow" of microwaves, with a blackbody temperature of about 3 K.
C) the measurement of the rotation of the Milky Way Galaxy.
D) the amount of gas and dust in the solar neighborhood.

Question 42

What is the temperature of the blackbody radiation that Earth receives from the Big Bang (the cosmic microwave background radiation)?

A) 30 K
B) 30 billion K
C) 3 K
D) 3000 K

Question 43

The cosmic background radiation is the

A) result of the radioactive decay of heavier, unstable elements produced in supernova explosions.
B) faint glow along the elliptic, caused by sunlight scattering from dust particles.
C) electromagnetic remnants of the incredibly hot, dense early universe.
D) radio noise from hot gas in rich clusters of galaxies.

Question 44

The Big Bang theory is the most widely accepted model of the early universe today. Which of these is NOT one of the reasons for this?

A) The observed expansion of the universe is consistent with the Big Bang theory.
B) No alternate theories have been proposed.
C) The observed cosmic microwave background is consistent with the Big Bang theory.
D) The observed cosmic neutrino background is consistent with the Big Bang theory.

Question 45

Who discovered the cosmic microwave background radiation, the radiation left over from the Big Bang?

A) Ralph Alpher and George Gamow
B) Arno Penzias and Robert Wilson
C) Anthony Hewish and Jocelyn Bell
D) Robert Dicke and P. J. E. Peebles

Question 46

When the intensity of the cosmic microwave background radiation is plotted against wavelength, what is the shape of the resulting curve?

A) emission lines, strongest and most densely concentrated in the microwave region
B) composite of many overlapping blackbody curves from gas clouds of different temperatures peaking in the microwaves
C) blackbody curve modified by many deep, overlapping absorption lines and several emission lines
D) essentially perfect blackbody spectrum peaking in the microwave region

Question 47

Astronomers detect the slight anisotropy in the cosmic microwave background by making redshift measurements: wavelengths coming from the direction of Aquarius are slightly longer and those from the direction of Leo are slightly shorter. This redshift is a

A) Doppler shift.
B) gravitational redshift.
C) cosmological redshift.
D) Doppler shift, gravitational redshift, or cosmological redshift since all three are one and the same thing.

Question 48

Which single observation is perhaps the strongest argument against the steady-state model of the universe and for the Big Bang model?

A) The number of supporters of the steady-state model is less than the number of supporters of the Big Bang model.
B) Astronomers have not observed matter being created from nothing in the space around Earth.
C) The universe is expanding.
D) The universe is bathed in a sea of microwaves coming from the edge of the visible universe.

Question 49

If the cosmic microwave background radiation is the radiation left over from the Big Bang, why is its temperature only 3 K?

A) The universe has expanded and cooled to the temperature now observed for the background radiation.
B) The cosmic microwave background is only the cool tail of the background radiation, but the higher energies are blocked by galaxies and intergalactic clouds.
C) The Big Bang was a cold explosion, not a hot explosion-its temperature was the same as the current temperature observed from the cosmic background radiation.
D) The cosmic background radiation observed now is not from the Big Bang at all-it is from cold, intergalactic hydrogen clouds that cover the sky.

Question 50

The cosmic background radiation that was left over after the Big Bang of the universe and that pervades all observable space has an effective blackbody temperature of approximately

A) 273 K.
B) 0 K.
C) 10 K.
D) 3 K.

Question 51

What was the COBE satellite designed to measure?

A) redshifts of objects at cosmological distances to obtain an accurate measurement of the Hubble constant
B) 21-cm radio radiation from intergalactic hydrogen
C) X-rays from quasars and other objects at cosmological distances
D) cosmic microwave background radiation

Question 52

Astronomers studying the cosmic microwave background have recently inferred the existence of another relic of the Big Bang that pervades the universe. What makes up this other background?

A) gamma rays
B) cosmic rays
C) magnetic fields
D) neutrinos

Question 53

How does the universe behave, according to the steady-state theory?

A) As the universe expands, new matter is created from which new galaxies form, thus maintaining a "steady state."
B) New matter is being continuously created, which adds to the absorption of light in the universe and makes distant galaxies seem farther and farther away.
C) The universe is static, not expanding or contracting, but new matter is being created so that as old galaxies die, new galaxies form to take their place.
D) The universe is static, neither expanding nor contracting, thus maintaining a "steady state" in which no change takes place.

Question 54

The greatest support for the Big Bang theory of cosmology came from the discovery of

A) the cosmic microwave background.
B) the cosmic neutrino background.
C) isotropy in the universe.
D) homogeneity in the universe.

Question 55

The cosmic background radiation is

A) the flux of visible radiation in empty space, contributed by all visible stars in the universe.
B) the radio noise generated by Earthbound transmitters, spreading out into space since about 1920.
C) the beam of atomic nuclei known as cosmic rays that continuously rain down on Earth from all directions in space.
D) low-intensity radio noise, with a 3 K blackbody temperature, almost uniform in intensity in all directions.

Question 56

The cosmic microwave background radiation forms a blackbody curve corresponding to a temperature of 2.73 K. What does Wien's law predict for the peak wavelength in this blackbody curve?

A) 0.654 mm
B) 1.07 mm
C) 21.1 cm
D) 2.73 m

Question 57

Who first predicted the existence of the cosmic microwave background radiation, the radiation left over from the Big Bang?

A) Ralph Alpher and George Gamow
B) Arno Penzias and Robert Wilson
C) Anthony Hewish and Jocelyn Bell
D) Robert Dicke and P. J. E. Peebles

Question 58

The cosmic microwave background was discovered by

A) rocket-borne telescopes that also discovered X-ray sources in space.
B) the Voyager 2 spacecraft during one of its "coasting" periods between planetary encounters.
C) scientists testing a new antenna and receiver for satellite communications.
D) the Infrared Astronomical Satellite (IRAS), which produced an all-sky infrared survey.

Question 59

What is the cosmic microwave background radiation?

A) uniform background of radiation from electrons spiraling in weak intergalactic magnetic fields
B) radiation left over from the Big Bang after the universe expanded and cooled
C) almost uniform background of radiation from distant, unresolved, overlapping galaxies
D) radiation from a very tenuous, ionized gas that fills the universe equally in all directions

Question 60

How was the cosmic microwave background radiation discovered?

A) using a microwave detector on the Hubble Space Telescope
B) using the Cosmic Background Explorer (COBE) spacecraft
C) using a communications antenna on Earth's surface
D) using the Ulysses spacecraft observing from above the Sun's north pole

Question 61

How many fundamental forces are known in science at the present time under normal conditions?

A) four
B) five
C) three
D) six

Question 62

The weak force

A) acted only during the Big Bang and has no known role in the universe at the present time.
B) holds the quarks together inside a proton or neutron.
C) attracts the electrons to the nucleus, holding the atom together.
D) acts during certain kinds of radioactive decay.

Question 63

When the isotropy of the cosmic microwave radiation was first realized, what effect did this discovery have on the contemporary theories of cosmology?

A) The discovery was a great support for the Big Bang cosmology that predicts this isotropy.
B) The discovery was a great support for the steady-state cosmology that predicts this isotropy.
C) The discovery was a great problem because it was prohibited by all the main cosmologies.
D) The discovery was a puzzle because the Big Bang cosmology does not predict this isotropy, although it does not prohibit it either.

Question 64

The effect that makes the cosmic microwave background appear slightly warmer in one direction and cooler in the opposite direction is

A) a basic asymmetry in the background radiation, related to its origin.
B) the Doppler shift caused by motion of the Milky Way Galaxy through space toward the constellation Leo.
C) microwave emission from cool, primordial (pregalactic) clouds of gas and dust in that direction.
D) the presence of large clusters of galaxies in only one direction.

Question 65

The physical force that controls the structure of the nucleus and binds together protons and neutrons is the

A) gravitational force.
B) weak nuclear force.
C) electromagnetic force.
D) strong nuclear force.

Question 66

How many fundamental forces are there in nature at the present time under normal conditions?

A) three: strong, electromagnetic, and gravitational
B) six: color, strong, weak, magnetic, electric, and gravitational
C) four: strong, weak, electromagnetic, and gravitational
D) five: strong, weak, magnetic, electric, and gravitational

Question 67

In relation to the universe, what does "isotropy" mean?

A) The universe has the same expansion speed at all distances.
B) The universe is the same at all distances.
C) The universe at any given distance is the same at all times.
D) The universe looks the same in all directions.

Question 68

What is the range of the gravitational force (the maximum distance over which it acts)?

A) 10¹³ m, or roughly the size of the solar system
B) 10²¹ m, or roughly the size of the Milky Way Galaxy
C) infinity
D) 10²⁶ m, or roughly the distance to the farthest quasars

Question 69

The one physical force that extends farthest in this universe and is NOT canceled out by other effects is the

A) weak nuclear force.
B) strong nuclear force.
C) electromagnetic force.
D) gravitational force.

Question 70

The cosmic microwave background radiation is not uniform over the sky-it is slightly hotter toward the constellation Leo and slightly cooler in the opposite direction, toward Aquarius. Why?

A) The difference is probably a statistical fluctuation and therefore not real.
B) The background radiation really is uniform; the observed difference is due to Earth's motion through the universe.
C) Earth is slightly off-center in the universe, so one side of the universe is a bit closer and the other is a bit farther away.
D) That is the way the universe began-hotter in one direction and cooler in the other.

Question 71

The Milky Way Galaxy is moving at about 600 km/s relative to the cosmic microwave background. How does this compare to Earth's speed in its orbit and to the speed of the solar system in its orbit around the galactic center?

A) This speed is less than both the speed of the solar system and Earth's orbital speed.
B) This speed is greater than Earth's orbital speed but less than the solar system's speed.
C) This speed is greater than the solar system's speed but less than Earth's speed in its orbit.
D) This speed is greater than both Earth's speed in its orbit and the solar system's speed.

Question 72

Which two forces are infinite in extent?

A) gravity and electromagnetism
B) gravity and the strong nuclear force
C) electromagnetism and the strong nuclear force
D) the two nuclear forces, strong and weak

Question 73

The Milky Way Galaxy is moving at about 600 km/s relative to the cosmic microwave background radiation. Why?

A) The Milky Way is being gravitationally attracted by several nearby superclusters of galaxies.
B) This speed is the orbital speed of the Local Group of galaxies around the Virgo cluster.
C) There is no particular reason. All galaxies have "small" random speeds in addition to the universal expansion, and 600 km/s is the speed of the Milky Way.
D) This speed is the orbital speed of the Milky Way Galaxy around the Andromeda Galaxy.

Question 74

The forces of gravity and electromagnetism are long-range forces, extending in principle from their source (mass and electric charge, respectively) to infinity. Why is it that, in the universe, only gravity extends to infinity, whereas electromagnetic forces are much more limited in extent?

A) Gravity and electromagnetism are one and the same force, with electromagnetic effects extending over limited spatial ranges and transforming into gravitational forces at large distances from matter.
B) Electromagnetic forces from charged particles will move other charged particles around to produce a uniform charge distribution and therefore zero electromagnetic forces, whereas gravity concentrates mass and enhances the overall gravity force.
C) Electromagnetic forces from positive charges are canceled by negative charges, whereas there are no negative "masses" to cancel the gravitational force.
D) All atoms are electrically neutral, so in reality the electromagnetic force never reaches beyond the size of an atomic nucleus.

Question 75

When is the weak nuclear force encountered?

A) when a quark is transformed into another quark
B) when a positively charged nucleus repels another positively charged nucleus in the core of a star like the Sun
C) when two quarks interact inside a proton or neutron
D) when an atom absorbs a photon and one of the electrons in the atom is sent into a higher energy level

Question 76

Why does the cosmic microwave background appear to be slightly warmer in one direction in the sky and slightly cooler in the opposite direction?

A) The warmer direction is the direction in which the Big Bang occurred; hence, astronomers are seeing the remnant of the explosion in this direction.
B) The universe is younger in one direction and therefore warmer.
C) The radiation in one direction is Doppler-shifted to shorter wavelengths by Earth's motion in space and to longer wavelengths in the other direction.
D) Large amounts of matter in the warmer direction have focused the radiation slightly by gravitational lensing, making this direction appear hotter.

Question 77

What do astronomers mean when they say that the universe is homogeneous?

A) The number of galaxies, averaged over large scales, is the same at any distance from Earth.
B) There are no mass concentrations anywhere in the universe.
C) The universe is static and unchanging.
D) At any given time, the universe looks the same in all directions.

Question 78

Which of the four fundamental forces holds the electrons in the atom?

A) strong nuclear force
B) gravitational force
C) weak nuclear force
D) electromagnetic force

Question 79

What is the range of the electromagnetic force (the maximum distance over which it acts)?

A) 10^-15 m (1 femtometer, or roughly the size of a proton)
B) 10^-9 m (1 nanometer, or roughly the size of a hydrogen atom)
C) a few thousand meters, or roughly the size of Earth
D) infinity

Question 80

Gravity holds galaxies together. What does the weak nuclear force hold together?

A) leptons (particles including electrons and neutrinos)
B) nothing
C) nuclei
D) quarks inside protons and neutrons