Deck 14: Cosmology

Question 1

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.

Answer 1

expansion of space, stretching the photon's wavelength while the photon is traveling toward Earth.

Question 2

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 we who are 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.

Answer 2

Spacetime itself is expanding, carrying the galaxies (or superclusters of galaxies) with it.

Question 3

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 3

Albert Einstein

Question 4

Which description is NOT consistent with the universe as envisioned by Isaac Newton?

A) infinite
B) static
C) having existed forever
D) expanding slowly

Question 5

The expansion of the universe takes place:

A) only between objects separated by vacuum; as a result, our bodies do not expand, but the Earth-Moon system does.
B) between all objects, even between the atoms in our 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 6

What causes 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 7

Which statement 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 8

Why did Einstein introduce his cosmological constant into the original field 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 9

Our consistent theories about the evolution of the universe begin:

A) before the Big Bang.
B) a fraction of a second after the Big Bang.
C) 30,000 years after the Big Bang.
D) 380,000 years after the Big Bang.

Question 10

What is the "cosmological redshift"?

A) the stretching of the wavelengths of photons as they travel through expanding space
B) the stretching of the wavelengths of photons by the Doppler shift because they are emitted by galaxies that are moving away from us
C) the 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 us through space
D) the stretching of the wavelengths of photons as they pass through absorbing matter in galaxies between us and the emitting galaxy

Question 11

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 12

Suppose an object is at rest and that it is emitting radiation.An observer also at rest in the same reference frame 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 13

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 14

The cosmological redshift in the light from distant galaxies is explained by which effect?

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 we on Earth see 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 us and is therefore more gravitationally redshifted.

Question 15

In the universe,we can 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 this expansion?

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

Question 16

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 17

Einstein chose his cosmological constant to be positive.Why did he make this choice?

A) The choice was arbitrary because he did not realize at the time that it had physical implications.
B) If he had chosen a negative constant, his solutions would have been imaginary rather than real.
C) Unlike Newton, Einstein did not believe in an infinite universe, and the positive constant was needed to make his solutions describe a finite universe.
D) The positive constant implies a positive force that was needed to counter the negative force (implying an inward force) that resulted without the constant.

Question 18

What do cosmologists study?

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

Question 19

Why did Newton view the universe as infinite in extent?

A) It was based on purely religious/philosophical grounds.
B) Newton had some idea of the scale of the universe because of the lack of observable parallax for even the closest stars. So, he reasoned, with the huge number of faint stars he could see through his telescope, the universe must go on infinitely in all directions.
C) Newton believed the universe was expanding outward. If it were finite in extent, it would long ago have stopped and would have begun to collapse.
D) If the universe had an edge, there would be an imbalance of forces on objects near the edge and they would not be in equilibrium.

Question 20

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

Question 21

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 pulls from the central supermassive black holes of galaxies that holds everything in the galaxies in place

Question 22

Who first proposed that the observed motion of galaxies away from Earth originated with a colossal,high-temperature explosion at the beginning of the universe?

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

Question 23

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

A) the rapid motions of some nearby stars, such as Barnard's star.
B) a background "glow" of microwaves, with 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 24

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 25

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

Question 26

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 IRAS satellite, which produced an all-sky infrared survey.

Question 27

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 28

According to Hubble's law,how old is the universe (H₀ = Hubble's 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 29

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 we now calculate, namely 13.7 billion years.
B) an age younger than 13.7 billion years.
C) an age older than 13.7 billion years.
D) a different value of the age, but more information is needed to estimate what it would be.

Question 30

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 explosion in which the universe was born.
D) radio noise from hot gas in rich clusters of galaxies.

Question 31

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) We have not observed matter being created from nothing in the space around us.
C) The universe is expanding.
D) The universe is bathed in a sea of microwaves coming from the edge of the visible universe.

Question 32

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 = 13.7 billion years.
B) The age would be less than 13.7 billion years.
C) The age would be greater than 13.7 billion years.
D) It is not possible to answer the question based only on this information.

Question 33

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 non-relativistic cosmological redshift and the Doppler shift provide the same result.

Question 34

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 35

When we use H₀ to calculate the age of the universe,we are making all of the following assumptions EXCEPT ONE.Which is the exception?

A) The universe is isotropic, that is, it has the same properties 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 36

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 37

Which statement about Hubble's original data is CORRECT?

A) Hubble's original data were just from the Local Group of galaxies. But the Hubble expansion applies to galaxy-to-galaxy distances within galaxy clusters, so he was able to see the universal expansion within these data.
B) Hubble's original data were for superclusters of galaxies, so he was able to see the effect of the expansion within these data.
C) The Hubble expansion does not apply to galaxy-to-galaxy distances, but the Doppler effect does. Since Hubble used only data from the Local Group, he was actually measuring only Doppler shifts.
D) The Hubble expansion does not apply to galaxy-to-galaxy distances, but it does apply to cluster-to-cluster distances. Hubble's original data were included galaxies beyond the Local Group, so he was able to see the universal expansion within these data.

Question 38

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

A) Doppler shift relationship. This was an error, and the calculations had to be repeated using the cosmological redshift relationship.
B) Doppler shift relationship. This was an error, and the calculations had to be repeated using the gravitational redshift relationship.
C) Doppler shift relationship. This was correct because the non-relativistic 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 39

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 40

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 41

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 (pre-galactic) clouds of gas and dust in that direction.
D) the presence of large clusters of galaxies in only one direction.

Question 42

We 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 43

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 horn antenna on Earth's surface
D) using the BOOMERANG balloon circling above Antarctica

Question 44

What is the Great Attractor?

A) a fifth fundamental force, in addition to the strong, weak, electromagnetic, and gravitational forces
B) a massive supercluster of galaxies that is gravitationally pulling on our Local Group
C) a supermassive black hole at the center of the Virgo cluster of galaxies
D) a concentration of primordial quantum fluctuations

Question 45

Who predicted the existence of the cosmic microwave background radiation,the radiation left over from the Big Bang,and began making preparations to detect it?

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

The Milky Way Galaxy is moving at about 600 km/s relative to the cosmic microwave background.How does this compare with Earth's speed in its orbit and with 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 47

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 48

Penzias and Wilson had no difficulty making their initial observation of the cosmic microwave background radiation at a wavelength of 7.35 millimeters.But it required other telescopes to verify the complete blackbody spectrum of the radiation.Why? (See Figure 14-4,Comins,Discovering the Essential Universe,6th ed.)

A) The microwave receiver of Penzias and Wilson could be pointed at only one region of the sky, and a complete sky scan was necessary for the full blackbody curve.
B) Penzias and Wilson had, by coincidence, been observing the curve near its peak, where the intensity was strongest. The rest of the curve required more sensitive receivers.
C) The peak of the curve and the sharp fall-off on the short wavelength side occur at wavelengths of 1 millimeter or shorter, and this radiation is blocked by Earth's atmosphere. Thus, balloons and satellites had to be used.
D) Because of the changing seasons, the source of this radiation moved out of the night sky for Penzias and Wilson soon after they made their initial observation, so further measurements had to be made by observers elsewhere on Earth.

Question 49

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 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 Hubble's 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

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 53

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 we now observe for the background radiation.
B) The cosmic microwave background radiation we observe is not cool-it is very hot, just like the Big Bang.
C) The Big Bang was a cold explosion, not a hot explosion-its temperature was the same as the current temperature we observe from the cosmic background radiation.
D) The cosmic background radiation we observe now is not from the Big Bang at all-it is from cold, intergalactic hydrogen clouds that cover the sky.

Question 54

The Big Bang theory is the most widely accepted model of the early universe today.Which statement 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 55

Why was the actual measurement of the cosmic microwave background so difficult?

A) Earth's atmosphere is almost opaque in the region of the spectrum where this radiation peaks (long-wavelength infrared/short wavelength microwaves).
B) It was never clear where in the spectrum this radiation would fall.
C) Because the radiation has spread out so much since its origin in the Big Bang, it is extremely faint.
D) The predicted frequency for this radiation was in a range not previously detected, so specialized equipment had to be designed and built.

Question 56

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

Question 57

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

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

Question 58

What is the Great Attractor?

A) a supermassive black hole at the center of the Milky Way Galaxy
B) an immense black hole thought to be at the center of the universe and a remnant of the cosmic singularity
C) a large collection of mass about 50 Mpc from Earth in the direction of the Hydra-Centaurus supercluster toward which the Local Group of galaxies is being drawn
D) an immense black hole somewhere in the universe from the accretion disk of which the cosmic 3-K background radiation is believed to be emitted

Question 59

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, we 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 60

What do we mean when we say that the universe is homogeneous?

A) At any given time and on a large enough scale, the universe looks the same at all locations.
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 61

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 62

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

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

Question 63

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 64

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 65

What is the range of the strong nuclear force compared with the size of the nucleus,10-¹⁴ m?

A) the same since it is the strong force that holds the nucleus together
B) 10 times larger than the size of an atomic nucleus
C) infinite since it has no limit
D) 10 times smaller than the size of an atomic nucleus

Question 66

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 is not prohibit it, either.

Question 67

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

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

Question 68

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 69

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 70

Physicists are attempting to develop a Theory of Everything.What would be unique about such a theory?

A) It would describe both relativistic and non-relativistic physics.
B) It would include the actions of the electroweak force.
C) It would be able to describe the universe during the Planck era.
D) It would be able to describe the universe before the Planck era.

Question 71

What is the electroweak force?

A) This is a fifth force, distinct from the original four, which helps to explain dark energy.
B) When charged particles of both signs (positive and negative) are closely mixed, the electromagnetic force-generally infinite in extent-is limited in its practical range. Under these circumstances, it is termed electroweak.
C) At sufficiently high temperatures, the electromagnetic force and the weak nuclear force are indistinguishable. This composite force is called electroweak.
D) At sufficiently high temperatures, the strong nuclear force and gravitational force disappear. At even higher temperatures, the weak nuclear force and the electromagnetic force combine to form the electroweak force. It is the only force that exists at this temperature.

Question 72

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

Question 73

When is the weak nuclear force encountered?

A) when a neutron is transformed into a proton with the ejection of an electron and a neutrino
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 74

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 75

The four physical forces at work in the universe are gravitational,electromagnetic,strong nuclear,and weak nuclear forces.Which two of these are very short-ranged,extending over distances of only about 10-¹⁵ m?

A) strong nuclear and electromagnetic forces
B) electromagnetic and weak nuclear forces
C) strong and weak nuclear forces
D) gravitational and electromagnetic forces

Question 76

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 77

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 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 78

The Theory of Everything is the attempt to describe all four fundamental forces as aspects of a single unified force.The force that has proved to be the MOST difficult to incorporate into such a theory is:

A) gravity.
B) electromagnetism.
C) the weak nuclear force.
D) the strong nuclear force.

Question 79

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 80

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

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