Deck 22: Modern Cosmology

Question 1

Which of the following is FALSE?

A)When the universe was young,matter worked to slow the expansion rate of the universe.
B)The Big Bang occurred approximately 13.7 billion years ago.
C)Only in the last 5 to 6 billion years has dark energy caused the universe's expansion rate to increase over time.
D)Throughout the age of the universe,dark energy has caused its expansion rate to increase over time.
E)Astrophysicists are unsure whether or not dark energy always will continue to increase the expansion rate of the universe.

Answer 1

Throughout the age of the universe,dark energy has caused its expansion rate to increase over time.

Question 2

Why does the overall mass and energy density of the universe decide its ultimate fate?

A)The greater the density of the universe,the more black holes will form,which will devour surrounding material more quickly.
B)The greater the density of the universe,the more gravitationally bound the universe will be.
C)The greater the density of the universe,the more massive stars it will contain,and the faster it will evolve.
D)The greater the density of the universe,the more stars it will form over time and the longer the universe will last.
E)The greater the density of the universe,the more supernova will explode,forcing the universe to expand forever.

Answer 2

The greater the density of the universe,the more gravitationally bound the universe will be.

Question 3

Astronomers have confirmed the Grand Unified Theory by observing that protons decay in laboratory experiments.

Answer 3

False

Question 4

Observations of Type I supernovae in distant galaxies confirm that the expansion of the universe is decreasing over time.

Question 5

Directly after the Big Bang,the universe was filled with a variety of charged particles,antiparticles,and photons.

Question 6

Dark energy is a force that continually decreases the expansion rate of the universe.

Question 7

The three fundamental forces of nature are gravity,electromagnetism,and the strong force.

Question 8

If the sum of the mass and energy density in the universe yields Ω < 1,then the universe will recollapse in a Big Crunch.

Question 9

The fact that the currently observed Ω_mass + Ω_Λ is very close to 1 means that its value has always been very close to 1.

Question 10

The ratio of the average density in all forms of matter (luminous and dark)in our universe to the critical density is approximately 0.3.

Question 11

In the superstring theory that successfully unites gravity and quantum mechanics,the universe must have 11 dimensions (10 spatial and 1 temporal).

Question 12

The critical density of the universe is closest to:

A)1 proton/m³
B)1 g/m³
C)1 kg/m³
D)1 M_Earth/m³
E)1 M_⨀/m³

Question 13

The four fundamental forces of nature are gravity,electromagnetism,the weak force,and the strong force.

Question 14

The ratio of the density of luminous matter in our universe to the critical density is 0.3.

Question 15

The concept of inflation helps solve both the problems of the flatness of the universe and smoothness of the cosmic background radiation.

Question 16

Gravity acts to __________ the expansion of the universe,and dark energy acts to __________ the expansion.

A)slow;slow
B)slow;speed up
C)speed up;slow
D)speed up;speed up

Question 17

The force that binds three quarks together to make up a proton or neutron is called the weak force.

Question 18

According to the theory of inflation.when the universe was approximately 1 second old,its size grew by a factor of 10³⁰.

Question 19

The weak force mediates the beta decay of neutrons into protons,electrons,and antineutrinos.

Question 20

The theory of inflation assumes that at some point in the future dark energy will decay and the universe will expand rapidly by a factor of 10³⁰.

Question 21

The universe can be infinite in size for which shapes of the universe?

A)open
B)closed
C)flat
D)closed and flat
E)open and flat

Question 22

Current observations suggest that the density of luminous matter,all matter,and dark energy are:

A)Ω _luminous = 0.1,Ω _mass = 0.3,Ω _Λ = 0.7
B)Ω _luminous = 0.02,Ω _mass = 0.5,Ω _Λ = 0.5
C)Ω _luminous = 0,Ω _mass = 0.1,Ω _Λ = 0.9
D)Ω _luminous = 0.02,Ω _mass = 0.3,Ω _Λ = 0.7
E)Ω _luminous = 0.1,Ω _mass = 0.2,Ω _Λ = 0.7

Question 23

To determine how the expansion rate of the universe has changed over time,astronomers directly measure the __________ for a sample of Type I supernovae in distant galaxies.

A)redshift and luminosity
B)redshift and brightness
C)redshift and distance
D)distance and luminosity
E)distance and brightness

Question 24

The observations that show that the expansion of the universe is speeding up tell us the universe must contain:

A)gravity
B)dark matter
C)a force opposing gravity
D)black holes
E)cosmic microwave background radiation

Question 25

What do astronomers believe is currently having the largest effect on the change in the expansion rate of the present-day universe?

A)dark matter
B)baryonic (normal)matter
C)dark energy
D)radiation pressure
E)gravity

Question 26

If the fate of the universe were determined SOLELY by what we currently know to be the total mass of the universe in luminous and dark matter (excluding dark energy),astronomers would predict that we live in a universe that will:

A)expand forever
B)slow its expansion but never reverse it
C)stop expanding and eventually collapse
D)oscillate between expansion and collapse
E)expand so quickly that the universe is ripped apart

Question 27

Observations of Type I supernovae in distant galaxies have shown that:

A)the star formation rate in galaxies decreases with increasing redshift
B)the expansion rate of the universe is increasing
C)the cosmological constant is zero
D)dark energy is negligible at the present time
E)there were more stars in the past than at the present time

Question 28

If Ω_mass = 0.5 today and there were no dark energy,the universe would:

A)expand forever
B)slow its expansion but never reverse it
C)stop expanding and eventually collapse
D)oscillate between expansion and collapse
E)expand so quickly that the universe is ripped apart

Question 29

In a closed (spherical)universe,the sum of the angles in a triangle is:

A)180 degrees
B)<180 degrees
C)120 degrees
D) >180 degrees
E)240 degrees

Question 30

Why would it be very improbable for our universe to have Ω _mass+ Ω_Λ =0.9?

A)It would quickly evolve to have a much different value of Ω_mass +Ω_Λ.
B)In order to exist,every universe must have Ω_mass + Ω_Λ =1.
C)We know Ω_mass = 1,based on the average density of galaxies.
D)The fluctuation in the CMB tell us that Ω_mass + Ω_Λ = 0.7.
E)Dark energy studies tell us Ω_Λ = 0.9.

Question 31

If gravity were slowing down the expansion of the universe,how would very distant galaxies differ from nearby galaxies?

A)Distant galaxies would have a larger value for H₀ than nearby galaxies.
B)Distant galaxies would have a smaller value for H₀ than nearby galaxies.
C)Distant galaxies would contain more dark energy than nearby galaxies.
D)Distant galaxies would contain less dark energy than nearby galaxies.
E)Distant and nearby galaxies would be the same.

Question 32

The flatness problem arises because only a universe with __________ can have that value forever.

A)Ω_mass +Ω_Λ= 0
B)Ω_mass +Ω_Λ =1
C)Ω_mass +Ω_luminous =1
D)Ω_luminous +Ω_Λ =1
E)Ω_luminous+ Ω_Λ =0

Question 33

If there were no dark energy in the universe,the value of __________ would determine the evolution and fate of the universe.

A)H₀
B)1/H₀
C)Ω_luminous
D)Ω_mass
E)Ω_Λ

Question 34

In the 1990s,astronomers found that distant Type I supernova were __________ than they expected,leading them to conclude that __________.

A)brighter;the universe's expansion rate was decreasing with time
B)brighter;the universe was finite in size
C)fainter;the universe's expansion rate has been increasing with time
D)fainter;the universe was infinite in size
E)fainter;the universe was finite in size

Question 35

The Big Rip could occur in a universe where the effect of __________ increases with time.

A)quantum mechanics
B)luminous matter
C)dark energy
D)gravity
E)dark matter

Question 36

From the analysis of distant Type I supernovae and the Cosmic Microwave Background,we know that the Universe is approximately

A)4.6 million years old
B)4.6 billion years old
C)6.5 thousand years old
D)13.7 million years old
E)13.7 billion years old

Question 37

What two properties of the universe are determined by the values of Ω _mass and Ω _Λ?

A)size and temperature
B)expansion rate and size
C)size and age
D)age and expansion rate
E)age and temperature

Question 38

In a universe with an accelerating expansion rate,the actual age of the universe is __________ the Hubble time.

A)larger than
B)smaller than
C)negligible compared to
D)the same as
E)independent of

Question 39

How does the existence of dark energy affect the expansion of the universe?

A)It is possible for the mass density of the universe to be below the critical density and still collapse.
B)It is possible for the mass density of the universe to be below the critical density and still expand forever.
C)It is impossible to have a collapsing universe,regardless of its density.
D)It is impossible to have an expanding universe,regardless of its density.
E)It is impossible for the mass density of the universe to be above the critical density and still expand forever.

Question 40

If Ω _mass + Ω _Λ = 1 today and dark energy were a cosmological constant,the universe would:

A)expand forever
B)slow its expansion but never reverse it
C)stop expanding and eventually collapse
D)oscillate between expansion and collapse
E)expand so quickly that the universe is ripped apart

Question 41

How would astronomers describe the antiparticle of an electron?

A)It would have the same charge but opposite spin.
B)It would have the same mass but opposite charge.
C)It would have the opposite charge and higher mass.
D)It would have the opposite spin and higher mass.
E)It would have the opposite charge but same spin.

Question 42

Which of the following is a FALSE statement about inflation?

A)Inflation occurred when the universe was < 10⁻³³ seconds old.
B)Inflation occurred when the universe expanded by a factor of approximately 10³⁰.
C)Inflation solves the horizon problem.
D)Inflation is currently driving the expansion of the universe.
E)Inflation solves the flatness problem.

Question 43

What is the Planck era?

A)the earliest moments after the Big Bang
B)a period when quantum mechanics is needed to describe spacetime in addition to particles
C)the time period when a theory of everything (TOE)is needed to understand the universe
D)When spacetime can be described as a quantum mechanical "foam" rather than a smooth sheet
E)all of the above

Question 44

In some particle physics theories,the universe must have more than three spatial dimensions,but we experience only three.Why would we not see the other spatial dimensions?

A)The other nine spatial dimensions are too small to be noticeable.
B)The other seven spatial dimensions are tightly wrapped around each other and have not expanded.
C)The other seven spatial dimensions undergo inflation and flatten themselves out.
D)The other nine spatial dimensions wrap around each another and form the temporal dimension.
E)The other seven spatial dimensions are completely full of dark matter.

Question 45

Which was a triumph of quantum electrodynamics (QED)?

A)QED predicted the existence of three carrier particles before they were discovered in laboratory experiments.
B)QED unites the strong and weak nuclear forces.
C)QED is an example of a theory of everything.
D)QED successfully explains the origin of quantum mechanical fluctuations in the CBR.
E)QED combined the electric and magnetic forces.

Question 46

What would the universe be like if there were complete symmetry between matter and antimatter?

A)It would look similar to our universe,but half of it would be composed of antimatter.
B)We would observe two universes,one an antimatter reflection of the other.
C)There would be no universe,because all of the matter and antimatter would have been annihilated.
D)There would be a universe,but it would be completely composed of photons from the CMB.
E)It would look similar to our universe,but the charges of all of the particles would be reversed.

Question 47

The standard model of particle physics is incomplete because it leaves which question(s)unanswered?

A)Why do neutrinos have mass?
B)Why is the strong nuclear force much stronger than the weak nuclear force?
C)How is gravity related to the other three fundamental forces?
D)How does gravity work over such long distances?
E)all of the above

Question 48

What was the temperature of the universe when a typical CMB photon was no longer able to spontaneously create an electron and positron pair? Note that a photon has an energy equal to E = hc/λ,the CMB at any point in time has a blackbody spectrum that peaks at a wavelength λ_peak = (2900 μm K)/T,and the mass of a single electron is 9 × 10⁻³¹ kg.

A)2000 K
B)400,000 K
C)2 million K
D)40 million K
E)2 billion K

Question 49

A grand unified theory unites which forces?

A)only electromagnetism,weak nuclear,and strong nuclear forces
B)only gravity and strong nuclear forces
C)only electromagnetism,gravity,and weak nuclear forces
D)only gravity and electromagnetism forces
E)all four known forces

Question 50

Grand unified theories are very attractive because they can explain:

A)why we have five fundamental forces in the universe today
B)why the Big Bang never made any antimatter
C)why the universe consists mostly of matter
D)why the CMB is very smooth
E)what happens inside a black hole

Question 51

At what stage in the universe's history do we think the asymmetry between matter and antimatter was created?

A)at the very moment the Big Bang occurred
B)around the time gravity separated out of the single superforce
C)around the time the strong force separated out of the grand unified theory
D)around the time the weak force and electromagnetism separated
E)around the time the electric and magnetic forces separated

Question 52

Quantum chromodynamics describes how __________ works.

A)gravity
B)the strong nuclear force
C)electricity
D)magnetism
E)light

Question 53

Why is the fact that the cosmic microwave background radiation (CMB)is very smooth considered a problem?

A)A universe as smooth as predicted by the CMB should not have formed as many galaxies as have been observed.
B)A universe as smooth as predicted by the CMB should have collapsed by now.
C)A universe as smooth as predicted by the CMB should be expanding much faster than we are now.
D)A universe as smooth as predicted by the CMB should never occur because quantum mechanical fluctuations would have been imprinted on it.
E)A universe as smooth as predicted by the CMB should never have formed any stars or galaxies.

Question 54

What can simultaneously solve both the flatness and horizon problems in cosmology?

A)GUT
B)quantum mechanics
C)TOE
D)inflation
E)dark energy

Question 55

In the superstring theory that successfully unites gravity and quantum mechanics,the universe must have:

A)four dimensions (three spatial and one temporal)
B)six dimensions (three spatial and three temporal)
C)seven dimensions (six spatial and one temporal)
D)nine dimensions (eight spatial and one temporal)
E)11 dimensions (10 spatial and 1 temporal)

Question 56

To verify whether or not some grand unified theories are correct,physicists are searching for:

A)the Big Rip
B)mini-black holes
C)antimatter
D)protons that decay
E)dark matter that decays

Question 57

Which of the following are NOT considered carrier particles used to mediate forces between other particles?

A)photons
B)gluons
C)gravitons
D)quarks
E)W+ particles

Question 58

In order to produce an electron and a positron,two photons must have a combined energy of:

A)E > 2m_ec²
B)E > m_ec²
C)E > 1⁄2m_ec²
D)E = m_ec²
E)This cannot happen.

Question 59

In the early universe,which type of particle and anti-particle first stopped being spontaneously formed out of photons in the CMB?

A)Protons and neutrons,because their formation requires a larger number of photons
B)Electrons and positrons,because their formation requires a smaller number of photons
C)Protons and antiprotons,because their formation requires higher energy photons
D)Electrons and neutrinos,because their formation requires lower energy photons
E)Protons,antiprotons,electrons,and neutrinos stopped forming at the same time.

Question 60

As the universe cooled shortly after the Big Bang,which was the first fundamental force to separate itself out from the others?

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

Question 61

Which of these are possible types of multiple universes that could exist?

A)parallel universes with different physics and different mathematical explanations
B)other parts of an infinite universe which are so far away that we cannot observe them
C)quantum mechanical parallel universes,which are created each time something happens that has a probability of occurring in a different way,such as a dice roll
D)a multiverse with constant inflation,where each universe forms due to quantum fluctuations stopping that inflation
E)all of the above

Question 62

Why does a unified force split to become two separate forces?

A)The universe expands so much that carrier particles become too dense.
B)The average energy of photons in the universe becomes less than the mass of the unified force's carrier particles.
C)Dark energy becomes significant at later times and forces the two to split.
D)The spatial dimensions split and so must the forces.
E)Too many particles are created for the unified force to manage.

Question 63

Which of these is a restatement of the anthropic principle?

A)Life evolves to create more complex species.
B)Any galaxy must have living things.
C)The values of physical constants must allow for our existence.
D)There must be other civilizations in the universe.
E)Dark energy will pull the universe apart.

Question 64

If there were enough mass to slow down the expansion rate of the universe,how would the Hubble constant measured using very distant galaxies be different from what is observed in galaxies that are closer to us? Explain your answer.Is this what we observe in our universe?

Question 65

What are the names of the two particles that mediate the electromagnetic force in quantum electrodynamics (QED)and the strong force in quantum chromodynamics (QCD)?

Question 66

If dark energy is currently causing the expansion rate of the universe to increase with time,does this mean that you should worry that the Sun,the Earth,and your body itself are expanding? Why or why not?

Question 67

What can solve the flatness and horizon problem in cosmology,and why?

Question 68

If the Hubble constant were larger than it is,how would that change the measured age of the universe? Explain your answer.

Question 69

Why does the sum of Ω_mass and Ω_Λ determine the shape of our universe?

Question 70

Put the following types of objects in order,starting with the first one to form after the Big Bang and ending with the last one to form:

A)neutral atoms,protons,nuclei
B)protons,nuclei,neutral atoms
C)nuclei,neutral atoms,protons
D)protons,neutral atoms,nuclei
E)nuclei,protons,neutral atoms

Question 71

What is the "flatness problem" in cosmology?

Question 72

Describe the four fundamental forces of nature by listing their names and describing what effect each force has on objects in the universe.

Question 73

Soon after the Big Bang,we believe the four fundamental forces of nature were united into one superforce,and __________ was the first to split off from the others.

A)the strong force
B)electromagnetism
C)the weak force
D)gravity
E)nucleosynthesis

Question 74

Why does the critical mass density of the universe depend on the value of Hubble's constant,H₀?

Question 75

In a universe with no dark energy,what will happen to the expansion of the universe in the future if: (a)Ω_mass> 1, (b)Ω_mass= 1,and (c)Ω_mass <1?

Question 76

If you found a globular cluster that had an age of 20 billion years,what cosmological observations would conflict with this observation?

Question 77

The critical mass density of the universe today is 9.5 × 10⁻²⁷ kg/m³.Using the current observed value of Ω_luminous,what is the average density of protons in the universe? If they were spread evenly throughout the universe,what would be their typical separation? Note that the typical separation between protons would be roughly equal to the cube root of the average volume occupied by one proton,and the mass of a proton is 1.7 × 10⁻²⁷ kg.

Question 78

What are two observations that,when combined,tell us that the universe has Ω_mass+ Ω_Λ = 1 and is flat?

Question 79

Explain what the uncertainty principle means,and how it relates to the horizon problem.

Question 80

Even with infinitely powerful telescopes,we can look back in time only until the time when

A)galaxies first formed
B)hydrogen and helium formed
C)stars first formed
D)gravity split off from a superforce
E)recombination happened