Question 1

The flatness problem in cosmology asks the question:

Accepted Answer

A) why is the sky dark at night? 
B) why was the density of the universe so close to the critical density just after the Big Bang? 
C) why are the four forces (strong, weak, electromagnetic, and gravitational) not unified in the present-day universe? 
D) why is the temperature of the cosmic background radiation so smooth (isotropic) around the sky? 
A) why is the sky dark at night? 
B) why was the density of the universe so close to the critical density just after the Big Bang? 
C) why are the four forces (strong, weak, electromagnetic, and gravitational) not unified in the present-day universe? 
D) why is the temperature of the cosmic background radiation so smooth (isotropic) around the sky?

Question 2

It has been shown that above 100 GeV in energy, intermediate vector bosons behave like photons. What is the significance of this in the early universe?

Accepted Answer

A) Light (the cosmic microwave background radiation) was emitted by the weak interaction. 
B) Above this energy matter behaved like radiation: the radiation-dominated era of the early universe. 
C) The weak and electromagnetic interactions were unified. 
D) The strong force separated from the electromagnetic force. 
A) Light (the cosmic microwave background radiation) was emitted by the weak interaction. 
B) Above this energy matter behaved like radiation: the radiation-dominated era of the early universe. 
C) The weak and electromagnetic interactions were unified. 
D) The strong force separated from the electromagnetic force.

Question 3

In the string theory of Edward Witten:

Accepted Answer

A) there are 11 dimensions, including two time dimensions (essentially "forward" and "backward"). 
B) all of the dimensions are coiled up tightly like coiled strings. 
C) the 11 dimensions include several dimensions that ought to be observable at very low temperatures. 
D) seven dimensions are coiled tightly like coiled strings. 
A) there are 11 dimensions, including two time dimensions (essentially "forward" and "backward"). 
B) all of the dimensions are coiled up tightly like coiled strings. 
C) the 11 dimensions include several dimensions that ought to be observable at very low temperatures. 
D) seven dimensions are coiled tightly like coiled strings.

Question 4

What is a virtual particle?

Accepted Answer

A) a collection of particles that acts like a single particle 
B) any particle that has no mass and is electrically neutral 
C) a particle that can never have any detectable effect whatsoever on the real universe 
D) a particle that exists for such a short time interval that we cannot detect it by direct measurement 
A) a collection of particles that acts like a single particle 
B) any particle that has no mass and is electrically neutral 
C) a particle that can never have any detectable effect whatsoever on the real universe 
D) a particle that exists for such a short time interval that we cannot detect it by direct measurement

Question 5

If gravity holds galaxies together and the electromagnetic force holds atoms together, what does the weak nuclear force hold together?

Accepted Answer

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

Question 6

Would you expect the neutrino-antineutrino background to be at a temperature above or below the 2.75 K of the cosmic microwave background? Why?

Accepted Answer

A) The neutrino-antineutrino background "escaped" from the primordial fireball long before the CMB. Thus, it has been cooling for a longer time and it should be at a lower temperature. 
B) The neutrino-antineutrino background is constantly undergoing annihilation, which produces high-energy gamma rays and heat. Thus, the temperature should be higher than the CMB. 
C) The threshold temperature of the neutrino is the highest of any pair of production particles. Thus, the temperature should be higher than the CMB. 
D) The neutrino-antineutrino background was produced at an earlier, hotter time in the history of the universe. Thus, this background should be hotter than the CMB. 
A) The neutrino-antineutrino background "escaped" from the primordial fireball long before the CMB. Thus, it has been cooling for a longer time and it should be at a lower temperature. 
B) The neutrino-antineutrino background is constantly undergoing annihilation, which produces high-energy gamma rays and heat. Thus, the temperature should be higher than the CMB. 
C) The threshold temperature of the neutrino is the highest of any pair of production particles. Thus, the temperature should be higher than the CMB. 
D) The neutrino-antineutrino background was produced at an earlier, hotter time in the history of the universe. Thus, this background should be hotter than the CMB.

Question 7

What do we expect for the lifetime of Population III stars?

Accepted Answer

A) These stars were almost pure hydrogen and helium, and such stars use only the hydrogen fusion reaction. Therefore, we expect their lifetimes were long. 
B) These stars were characterized by almost zero metallicity, and such stars require large masses to collapse. With these large masses, we expect that their lifetimes were long. 
C) These stars were characterized by almost zero metallicity, and such stars require large masses and consequently high central temperatures to collapse. With high central temperatures, we expect their lifetimes were short. 
D) Since they were formed as early as 400 million years after the Big Bang, and we still find large numbers of them currently in existence, we know that their lifetimes are extremely long. 
A) These stars were almost pure hydrogen and helium, and such stars use only the hydrogen fusion reaction. Therefore, we expect their lifetimes were long. 
B) These stars were characterized by almost zero metallicity, and such stars require large masses to collapse. With these large masses, we expect that their lifetimes were long. 
C) These stars were characterized by almost zero metallicity, and such stars require large masses and consequently high central temperatures to collapse. With high central temperatures, we expect their lifetimes were short. 
D) Since they were formed as early as 400 million years after the Big Bang, and we still find large numbers of them currently in existence, we know that their lifetimes are extremely long.

Question 8

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

Accepted Answer

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

Question 9

If the average mass density ρ0 had been less than the critical density ρc in the early universe, what might have been the likely result?

Accepted Answer

A) The universe would have expanded very rapidly, and matter would not have clumped together to form galaxies. 
B) The universe's mass would have clumped together in a relatively short time and collapsed to a singularity like that from which it emerged. 
C) Cosmic inflation would not have occurred. 
D) The cosmic microwave background radiation would not have been created. 
A) The universe would have expanded very rapidly, and matter would not have clumped together to form galaxies. 
B) The universe's mass would have clumped together in a relatively short time and collapsed to a singularity like that from which it emerged. 
C) Cosmic inflation would not have occurred. 
D) The cosmic microwave background radiation would not have been created.

Question 10

To what does the phrase "Jeans length" refer?

Accepted Answer

A) the maximum distance over which a temperature fluctuation can occur in a "connected" universe 
B) the minimum diameter of a density fluctuation that can collapse gravitationally to form a galaxy or other astronomical object 
C) the minimum distance over which a temperature fluctuation can occur in a "connected" universe 
D) the maximum diameter of a density fluctuation that can collapse gravitationally to form a galaxy or other astronomical object 
A) the maximum distance over which a temperature fluctuation can occur in a "connected" universe 
B) the minimum diameter of a density fluctuation that can collapse gravitationally to form a galaxy or other astronomical object 
C) the minimum distance over which a temperature fluctuation can occur in a "connected" universe 
D) the maximum diameter of a density fluctuation that can collapse gravitationally to form a galaxy or other astronomical object

Question 11

During the first one-ten-thousandth second (10-4 s) of the life of the universe, antiprotons were very common. For every billion antiprotons, how many protons were there?

Accepted Answer

A) an unknown number, because the early universe was opaque and we cannot see what conditions were like then 
B) 1 billion and 1, thus producing the matter we see today 
C) 10 billion, thus producing the dark matter we see today 
D) exactly 1 billion, because protons and antiprotons were created in equal numbers 
A) an unknown number, because the early universe was opaque and we cannot see what conditions were like then 
B) 1 billion and 1, thus producing the matter we see today 
C) 10 billion, thus producing the dark matter we see today 
D) exactly 1 billion, because protons and antiprotons were created in equal numbers

Question 12

What is the difference between the virtual electron and virtual positron created spontaneously in the vacuum and the electron-positron pair created from a high-energy gamma ray?

Accepted Answer

A) They are exactly the same. 
B) The particles created by the gamma ray are real. They can last forever if they do not annihilate. The virtual particles must recombine to become part of the vacuum within a very short time. Only under very special circumstances can they become real. 
C) The particles created from the vacuum are real. They can last forever if they do not annihilate. The particles created from the gamma ray must recombine within a very short time. Only under very special circumstances can they become real. 
D) The virtual particles have positive and negative mass, whereas the particles created by the gamma ray have positive mass. 
A) They are exactly the same. 
B) The particles created by the gamma ray are real. They can last forever if they do not annihilate. The virtual particles must recombine to become part of the vacuum within a very short time. Only under very special circumstances can they become real. 
C) The particles created from the vacuum are real. They can last forever if they do not annihilate. The particles created from the gamma ray must recombine within a very short time. Only under very special circumstances can they become real. 
D) The virtual particles have positive and negative mass, whereas the particles created by the gamma ray have positive mass.

Question 13

The constant creation and annihilation of virtual pairs of particles and antiparticles causes a slight change in the wavelengths of the hydrogen spectral lines. This effect is called the:

Accepted Answer

A) Wolf effect. 
B) Rutherford shift. 
C) Lamb shift. 
D) Einstein effect. 
A) Wolf effect. 
B) Rutherford shift. 
C) Lamb shift. 
D) Einstein effect.

Question 14

What is the situation with respect to matter and antimatter in the universe today?

Accepted Answer

A) There is perfect symmetry and balance between matter and antimatter. 
B) There is a slight imbalance between matter and antimatter, with about one matter particle in excess for every billion matter-antimatter pairs. 
C) There is far more matter than antimatter in the universe. 
D) There is far more antimatter than matter in the universe. 
A) There is perfect symmetry and balance between matter and antimatter. 
B) There is a slight imbalance between matter and antimatter, with about one matter particle in excess for every billion matter-antimatter pairs. 
C) There is far more matter than antimatter in the universe. 
D) There is far more antimatter than matter in the universe.

Question 15

Which of the following statements correctly describes the "flatness problem" in cosmology?

Accepted Answer

A) Observations of the distant universe indicate that the universe is at least moderately flat, yet matter creates lumps in the geometry of spacetime. Therefore it is hard to account for the observed flatness. 
B) The density of the universe must have been equal to the critical density to a precision of 50 decimal places in order for us to see the universe we see today. This astounding flatness is hard to account for. 
C) The universe appears to have a hyperbolic geometry to within observational error, yet the universe is expanding, and expanding universes have to be flat. 
D) The universe appears to be flat to within observational error, yet the universe is expanding, and it is impossible for an expanding universe to be flat. 
A) Observations of the distant universe indicate that the universe is at least moderately flat, yet matter creates lumps in the geometry of spacetime. Therefore it is hard to account for the observed flatness. 
B) The density of the universe must have been equal to the critical density to a precision of 50 decimal places in order for us to see the universe we see today. This astounding flatness is hard to account for. 
C) The universe appears to have a hyperbolic geometry to within observational error, yet the universe is expanding, and expanding universes have to be flat. 
D) The universe appears to be flat to within observational error, yet the universe is expanding, and it is impossible for an expanding universe to be flat.

Question 16

Which of the four fundamental forces holds the protons in the nucleus of an atom together?

Accepted Answer

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

Question 17

At what point in the age of the universe did it cool to a temperature of about 3 K?

Accepted Answer

A) at the end of the quark confinement 
B) at the end of the deuterium bottleneck 
C) very recently 
D) when the temperature reached the proton threshold 
A) at the end of the quark confinement 
B) at the end of the deuterium bottleneck 
C) very recently 
D) when the temperature reached the proton threshold

Question 18

Each of the following is an attribute of the Kaluza-Klein theories EXCEPT one. Which one is the EXCEPTION?

Accepted Answer

A) The theories have at least four space dimensions. 
B) The dimensions we cannot see are curled tightly into loops. 
C) Different loop vibrations correspond to particles with different masses. 
D) In the new theories, gravitation no longer has an effect on space. 
A) The theories have at least four space dimensions. 
B) The dimensions we cannot see are curled tightly into loops. 
C) Different loop vibrations correspond to particles with different masses. 
D) In the new theories, gravitation no longer has an effect on space.

Question 19

Energy and mass are equivalent according to Einstein, and both can be measured in electron volts. (1 eV is the energy acquired by an electron when accelerated through 1 volt.) If the rest mass of an electron is 511 keV, what is the threshold energy of a gamma-ray photon in order that it can undergo electron pair production?

Accepted Answer

A) 1.533 MeV 
B) 1.022 MeV 
C) 0 eV, because it produces a particle-antiparticle pair 
D) 511 keV 
A) 1.533 MeV 
B) 1.022 MeV 
C) 0 eV, because it produces a particle-antiparticle pair 
D) 511 keV

Question 20

The cosmic microwave background of photons is observed to have a temperature of about 3 K. What is believed to be the present temperature of the cosmic neutrino-antineutrino background?

Accepted Answer

A) less than 3 K-the microwave background is warmer because it received extra energy from the annihilation reaction that produced it. 
B) 3 K-the expansion of the universe is the same for all particles in it. 
C) 4 K-the universe was hotter when it became transparent to neutrinos. 
D) 1,000,000 K-the neutrinos do not interact with matter and therefore have not been redshifted. 
A) less than 3 K-the microwave background is warmer because it received extra energy from the annihilation reaction that produced it. 
B) 3 K-the expansion of the universe is the same for all particles in it. 
C) 4 K-the universe was hotter when it became transparent to neutrinos. 
D) 1,000,000 K-the neutrinos do not interact with matter and therefore have not been redshifted.

Exam 26: Exploring the Early Universe

The flatness problem in cosmology asks the question:

It has been shown that above 100 GeV in energy, intermediate vector bosons behave like photons. What is the significance of this in the early universe?

In the string theory of Edward Witten:

What is a virtual particle?

If gravity holds galaxies together and the electromagnetic force holds atoms together, what does the weak nuclear force hold together?

Would you expect the neutrino-antineutrino background to be at a temperature above or below the 2.75 K of the cosmic microwave background? Why?

What do we expect for the lifetime of Population III stars?

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

If the average mass density ρ0 had been less than the critical density ρc in the early universe, what might have been the likely result?

To what does the phrase "Jeans length" refer?

During the first one-ten-thousandth second (10-4 s) of the life of the universe, antiprotons were very common. For every billion antiprotons, how many protons were there?

What is the difference between the virtual electron and virtual positron created spontaneously in the vacuum and the electron-positron pair created from a high-energy gamma ray?

The constant creation and annihilation of virtual pairs of particles and antiparticles causes a slight change in the wavelengths of the hydrogen spectral lines. This effect is called the:

What is the situation with respect to matter and antimatter in the universe today?

Which of the following statements correctly describes the "flatness problem" in cosmology?

Which of the four fundamental forces holds the protons in the nucleus of an atom together?

At what point in the age of the universe did it cool to a temperature of about 3 K?

Each of the following is an attribute of the Kaluza-Klein theories EXCEPT one. Which one is the EXCEPTION?

The cosmic microwave background of photons is observed to have a temperature of about 3 K. What is believed to be the present temperature of the cosmic neutrino-antineutrino background?

Astronomy and the Universe

Knowing the Heavens

Eclipses and the Motion of the Moon

Gravitation and the Waltz of the Planets

The Nature of Light

Optics and Telescopes

Comparative Planetology I: Our Solar System

Comparative Planetology II: the Origin of Our Solar System

The Living Earth

Our Barren Moon

Mercury, Venus, and Mars: Terrestrial, yet Unique

Jupiter and Saturn: Lords of the Planets

Jupiter and Saturns Satellites of Fire and Ice

Uranus, Neptune, Pluto, and the Kuiper Belt: Remote Worlds

Asteroids, Comets, and Impacts

Our Star, the Sun

The Nature of the Stars

The Birth of Stars

Stellar Evolution: on and After the Main Sequence

Stellar Evolution: The Death of Stars

Stellar Remnants: Neutron Stars and Black Holes

Our Galaxy

Galaxies

Quasars and Active Galaxies

Cosmology: The Origin and Evolution of the Universe

The Search for Extraterrestrial Life

Filters

If the average mass density ρ₀ had been less than the critical density ρ_c in the early universe, what might have been the likely result?

During the first one-ten-thousandth second (10^-4 s) of the life of the universe, antiprotons were very common. For every billion antiprotons, how many protons were there?