Question 1

Astrophysicists believe the dominant hot spots in the cosmic background radiation should be about 1° in angular size if the universe is flat.What do experimental measurements of this angular size tell us?
A) The measurements show angular sizes of less than 1°,which suggests that the universe is spherical.
B) The measurements show angular separations of about 1°,which suggests that the universe is flat.
C) The measurements show angular sizes larger than 1°,which suggests that the universe is hyperbolic.
D) The measurements thus far are inconclusive.

Accepted Answer

Experimental measurements of the angular size of dominant hot spots in the cosmic background radiation show an angular separation of about 1°, which supports the hypothesis that the universe is flat. If the angular separation was less than 1°, it would suggest a spherical universe, and if it was larger than 1°, it would suggest a hyperbolic universe. However, the measurements support a flat universe.

Question 2

What method is being used to discover whether we live in an unbounded universe,in which expansion will continue forever,or a bounded universe,in which expansion will eventually turn into contraction and lead us to recollapse? A) Careful monitoring of the Moon-Earth distance to detect the slowdown of the expansion of the universe B) Measurement of the deviation from uniformity of the cosmic background radiation C) Measurement of the curvature of the Hubble relationship,v = H₀d,at large distances D) Measurement of the bending of light by distant galaxies as it follows the curvature of space

Accepted Answer

Measurement of the curvature of the Hubble relationship, $v = H_0d$, at large distances is used to determine the fate of the universe's expansion. This involves observing the relationship between the velocity at which galaxies are receding from us and their distance, to infer the overall geometry and density of the universe, which in turn indicates whether the universe will expand forever or eventually recollapse.

Question 3

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) acts during certain kinds of radioactive decay.
D) attracts the electrons to the nucleus,holding the atom together.

Accepted Answer

The weak force is one of the four fundamental forces of nature (along with gravity, electromagnetism, and the strong force) and it is responsible for certain kinds of radioactive decay.

Question 4

What kind of curvature (geometry of space)does the universe have if the universe is unbounded (density < critical density)?
A) Flat
B) Closed
C) Open
D) Curvature does not depend on density.

Accepted Answer

If the universe is unbounded (density < critical density), it means that the universe will continue to expand forever. In this scenario, the geometry of the universe is open, meaning it has negative curvature. This is because the gravitational pull of matter in the universe is not strong enough to cause the universe to collapse in on itself.

Question 5

In cosmology,the phrase "critical density" refers to the
A) smallest density that will produce inflation of the universe.
B) density below which stars will never form.
C) density above which the universe is opaque to radiation.
D) density needed to produce precisely flat space,on average,throughout the universe.

Accepted Answer

The critical density is the density needed to produce precisely flat space, on average, throughout the universe. If the actual density of the universe is less than the critical density, then the universe is open and will expand forever. If the actual density is greater than the critical density, then the universe is closed and will eventually collapse in on itself.

Question 6

Which parameter of the present universe,more than any other,is considered to be critical in determining the ultimate fate of the universe?
A) The average density of neutrinos
B) The average density of matter
C) The average density of black holes throughout the universe
D) The average density of photons of radiation

Accepted Answer

The average density of matter is the most critical parameter in determining the ultimate fate of the universe. If the average density of matter is high, then the universe will eventually stop expanding and collapse in on itself in a "big crunch". If the average density of matter is low, then the universe will continue to expand forever. This is known as the critical density and is currently estimated to be around 5 atoms per cubic meter.

Question 7

If space has a flat geometry,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).

Accepted Answer

In a flat geometry, the geometry of space remains constant over large distances. This means that parallel lines will always remain parallel and will never meet or cross. Therefore, the two initially parallel flashlight beams will continue to travel parallel to each other and will never converge or diverge.

Question 8

The degree of "flatness" of the universe,which determines whether we live in an open or a closed universe,has been determined recently by measuring the
A) average density of matter compared to the average density of radiation energy.
B) typical size of the "hot spots" in the structure of the cosmic microwave background.
C) hemispheric asymmetry in the temperature of the cosmic microwave background radiation.
D) extent of the bending of light from distant galaxies,the so-called "lensing."

Accepted Answer

The typical size of the "hot spots" in the structure of the cosmic microwave background is used to determine the degree of flatness of the universe. Specifically, a flat universe would have certain characteristic hot spot sizes, whereas a closed or open universe would have different hot spot sizes.

Question 9

The present universe seems to require a "cosmological constant" equivalent to that introduced into general relativity by Einstein when his theory would not explain the expected static universe.What is the effect on the evolution of the present universe of the "new" cosmological constant?
A) It produces a pressure to oppose the mutual gravitational pull of all the matter in the universe,accelerating its expansion.
B) It is a term that accounts for the negative gravity generated by antimatter in the universe,the presence of which will produce an accelerated expansion.
C) It just balances gravity to allow the universe to remain static,as Einstein predicted.
D) It produces an extra attractive force in addition to gravity,slowing down the expansion of the universe.

Accepted Answer

The "new" cosmological constant, also known as dark energy, produces a pressure that opposes the mutual gravitational pull of all matter in the universe, causing an accelerating expansion of the universe. This has been observed through various observational methods such as the measurement of the cosmic microwave background radiation and the redshifting of distant supernovae.

Question 10

What kind of curvature (geometry of space)does the universe have if the universe is bounded (density > critical density)?
A) Flat
B) Closed
C) Open
D) Curvature does not depend on density.

Accepted Answer

If the universe is bounded (density > critical density), it would have a closed curvature, meaning it is finite and would eventually loop back on itself.

Question 11

What is "dark energy"?
A) The energy associated with the matter that has fallen into a black hole
B) The matter-energy needed to bridge the gap between the energy we see or infer and the energy needed to make the universe flat
C) The energy associated with "dark matter"
D) The unseen matter-energy needed to make the observed curvature of space spherical (as we believe it should be),whereas the observed matter-energy only makes it hyperbolic

Accepted Answer

Dark energy is the hypothesized form of energy that is believed to be responsible for the accelerating expansion of the universe. It is needed to bridge the gap between the energy we see or infer and the energy needed to make the universe flat.

Question 12

Recent results from very bright supernovae in very distant galaxies seem to indicate that the expansion of the universe
A) is continuing at a constant rate and has done so since just after the Big Bang.
B) has now stopped and the universe will shortly begin to contract again toward a recollapse.
C) is accelerating (speeding up).
D) is decelerating (slowing down).

Accepted Answer

Recent results from very bright supernovae have shown that they are actually fainter than expected, indicating that they are farther away than predicted. This suggests that the expansion of the universe is accelerating, which is only possible if there is some sort of repulsive force at work (such as dark energy). Option A is incorrect, as a constant rate of expansion would not explain the observed faintness of very distant supernovae. Option B is also incorrect, as there is no evidence to suggest that the expansion has stopped. Option D is also incorrect, as slowing down would lead to a cessation of expansion at some point, which is not what the data show.

Question 13

Opposite sides of the universe have the same temperature,yet according to the standard Big Bang theory,these points are too far apart for light to have traveled from one side to the other in the age of the universe;that is,they cannot have exchanged heat to even out their temperature.Why,then,do they have the same temperature?
A) Light (and heat)could travel much faster in the early universe,allowing them to exchange heat while the universe was young.
B) The expansion of the universe has always been the same everywhere;therefore,all parts of the universe have the same temperature,regardless of whether they have ever exchanged heat or not.
C) Pure coincidence
D) They were originally close together and evened out their temperature,then a rapid inflation of the universe carried them far apart.

Accepted Answer

The most widely accepted explanation for this phenomenon is that the opposite sides of the universe were once close enough to exchange heat and even out their temperature. However, during a period of rapid inflation early in the universe's history, they were quickly carried apart and became too distant for light or heat to travel between them. This phenomenon is known as the "horizon problem." Therefore, choice D is the best answer.

Question 14

What kind of curvature (geometry of space)does the universe have if the universe is just bounded (density = critical density)?
A) Flat
B) Closed
C) Open
D) Curvature does not depend on density.

Accepted Answer

If the universe is just bounded with a density equal to the critical density, it means that the curvature of space is flat. This is because the critical density is the amount of matter and energy needed for the universe to be exactly flat. If the actual density is equal to the critical density, then the universe must be flat.

Question 15

How many fundamental forces are known in science?
A) Five
B) Three
C) Four
D) Six

Accepted Answer

Currently, four fundamental forces are known in science. They are gravitational force, electromagnetic force, strong nuclear force, and weak nuclear force.

Question 16

The isotropy of the cosmic microwave background radiation (same temperature in all directions)indicates that
A) the universe has always been dominated by matter.
B) the universe had an early period of inflation in which regions initially in contact were carried out of contact with each other.
C) the universe did not begin to expand significantly until after the era of recombination.
D) regions that appear to us to be on opposite sides of the visible universe are in fact in close contact with each other.

Accepted Answer

The isotropy of the cosmic microwave background radiation indicates that regions of the universe that appear to be on opposite sides (i.e. in different directions) of the visible universe have the same temperature, suggesting that they were once in contact with each other. This supports the idea of an early period of inflation in which the universe rapidly expanded, carrying initially in-contact regions out of contact with each other and smoothing out the universe on large scales.

Question 17

How many fundamental forces are there in nature?
A) Three: strong,electromagnetic,and gravitational
B) Six: color,strong,weak,magnetic,electric,and gravitational
C) Five: strong,weak,magnetic,electric,and gravitational
D) Four: strong,weak,electromagnetic,and gravitational

Accepted Answer

According to our current understanding of physics, there are four fundamental forces in nature: strong, weak, electromagnetic, and gravitational. Option A is incorrect as it doesn't include weak force. Option B is incorrect as there is no magnetic force, but it includes color which is not a fundamental force. Option C is incorrect as it includes magnetic force which is a manifestation of electromagnetic force, and also includes color.

Question 18

Which of the four fundamental forces holds the electrons in the atom?
A) Gravitational force
B) Weak nuclear force
C) Electromagnetic force
D) Strong nuclear force

Accepted Answer

The electromagnetic force holds the electrons in the atom. This force is responsible for the interaction between charged particles, such as the negatively charged electrons orbiting around the positively charged nucleus in an atom.

Question 19

What is the range of the gravitational force (the maximum distance over which it acts)?
A) 1026 m,or roughly the distance to the farthest quasars
B) Infinity
C) 1013 m,or roughly the size of the solar system
D) 1021 m,or roughly the size of the Milky Way Galaxy

Accepted Answer

The range of gravitational force is infinite, meaning that it acts over any distance, no matter how small or large.

Question 20

Immediately after the cosmological singularity,the four forces were indistinguishable.Then they began to "branch off" and become separate.Which was the first of the four to branch off?
A) Gravitation
B) The weak force
C) The strong force
D) Electromagnetism

Accepted Answer

Gravitation was the first force to separate from the unified forces shortly after the Big Bang, leading to the distinct forces we observe today.

Quiz 15: Observing the Evolution of the Universe

Astrophysicists believe the dominant hot spots in the cosmic background radiation should be about 1° in angular size if the universe is flat.What do experimental measurements of this angular size tell us?

What method is being used to discover whether we live in an unbounded universe,in which expansion will continue forever,or a bounded universe,in which expansion will eventually turn into contraction and lead us to recollapse?

The weak force

What kind of curvature (geometry of space) does the universe have if the universe is unbounded (density < critical density) ?

In cosmology,the phrase "critical density" refers to the

Which parameter of the present universe,more than any other,is considered to be critical in determining the ultimate fate of the universe?

If space has a flat geometry,what will happen to two initially parallel flashlight beams as they traverse billions of light-years of space?

The degree of "flatness" of the universe,which determines whether we live in an open or a closed universe,has been determined recently by measuring the

The present universe seems to require a "cosmological constant" equivalent to that introduced into general relativity by Einstein when his theory would not explain the expected static universe.What is the effect on the evolution of the present universe of the "new" cosmological constant?

What kind of curvature (geometry of space) does the universe have if the universe is bounded (density > critical density) ?

What is "dark energy"?

Recent results from very bright supernovae in very distant galaxies seem to indicate that the expansion of the universe

What kind of curvature (geometry of space) does the universe have if the universe is just bounded (density = critical density) ?

How many fundamental forces are known in science?

The isotropy of the cosmic microwave background radiation (same temperature in all directions) indicates that

How many fundamental forces are there in nature?

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

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

Immediately after the cosmological singularity,the four forces were indistinguishable.Then they began to "branch off" and become separate.Which was the first of the four to branch off?