Deck 22: Cosmology

Question 1

As a result of our universe undergoing an accelerated expansion,

A) ( $\Omega$ _$\bigwedge$ must be exactly zero.)
B) the fate of the universe is exclusively dictated by ( $\Omega$ _m.)
C) the mass density must be larger than the critical density.
D) the only possible outcome is the Big Crunch.
E) the age of the universe is currently greater than the Hubble time.

Answer 1

the age of the universe is currently greater than the Hubble time.

Question 2

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

A) H₀
B) 1/H₀
C) G
D) ( $\Omega$ _m)
E) ( $\Omega$ _$\bigwedge$ )

Answer 2

( $\Omega$ _m)

Question 3

In modern cosmology, Einstein's cosmological constant is

A) an example of dark energy that causes an accelerated expansion of the universe.
B) vanishingly zero.
C) another name for the critical density of the universe.
D) the only explanation for an infinite universe.
E) of no use, as it predicts a static universe.

Answer 3

an example of dark energy that causes an accelerated expansion of the universe.

Question 4

Mass density acts to ________ the expansion of the universe, and dark energy acts to ________ the expansion.

A) slow down; slow down
B) slow down; speed up
C) speed up; slow down
D) speed up; speed up
E) slow down; stabilize

Question 5

If $\Omega$ _m + $\Omega$ _$\bigwedge$ =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 it is ripped apart.

Question 6

The "Big Crunch" scenario applies to a universe with

A) a large, positive cosmological constant.
B) more black holes than stars.
C) a gravitational force that increases with time.
D) a density greater than the critical density.
E) a density less than the critical density.

Question 7

The accelerated expansion of the universe was observationally discovered using

A) Type Ia supernovae.
B) Cepheid variables.
C) RR Lyrae.
D) stellar parallax.
E) colors of galaxies.

Question 8

Which of the following has the greatest effect on the expansion rate of today's universe?

A) dark matter
B) luminous matter
C) dark energy
D) radiation pressure
E) nuclear decays

Question 9

If $\Omega$ _m =0.5 today and there were no dark energy, the universe would

A) expand forever.
B) slow its expansion and eventually stop.
C) stop expanding and eventually collapse.
D) oscillate between expansion and collapse.
E) expand so quickly that it would be ripped apart.

Question 10

In the 1990s, astronomers studying distant Type Ia supernovae discovered that the

A) universe's expansion rate has been decreasing with time.
B) universe is finite in size.
C) universe's expansion rate has been increasing with time.
D) rate of supernova explosions has been increasing with time.
E) universe's expansion rate has stayed constant with time.

Question 11

If the Hubble constant had a value of 50 km/s/Mpc instead of 70 km/s/Mpc, the value of the critical density $\Omega$ ₀ would be about

A) twice as large.
B) half as much.
C) the same.
D) 1.4 times smaller.
E) 1.4 times larger.

Question 12

If the fate of the universe were determined solely by what is currently known 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 and eventually reach a steady state.
C) stop expanding and eventually collapse.
D) oscillate between expansion and collapse.
E) expand so quickly that it will rip apart.

Question 13

The effect of matter on the universe is to

A) amplify the effects of dark energy.
B) "smooth out" the shape of space at all scales.
C) accelerate expansion.
D) decelerate expansion.
E) do nothing, as mass has no effect on the large-scale universe at any time.

Question 14

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

A) ( $\Omega$ _m = 0.3 and $\Omega$ _$\bigwedge$ 0 =0.7, respectively.)
B) ( $\Omega$ _m = 0.02 and $\Omega$ _$\bigwedge$ = 0.5, respectively.)
C) ( $\Omega$ _m = 0.0 and $\Omega$ _$\bigwedge$ =0.9, respectively.)
D) ( $\Omega$ _m =0.7 and $\Omega$ _$\bigwedge$ =0.3, respectively.)
E) ( $\Omega$ _m = 0.02 and $\Omega$ _$\bigwedge$ = 0.0, respectively.)

Question 15

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) an effect opposing gravity.
D) black holes.
E) cosmic microwave background radiation.

Question 16

To determine how the expansion rate of the universe has changed over time, astronomers directly measure the ________ for a sample of the Type Ia 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 17

If the material in the universe was at the critical density, expansion would

A) continue at the current rate forever.
B) increase at an accelerating rate.
C) continually slow, but never quite stop.
D) never occur.
E) eventually slow, stop, and then reverse.

Question 18

The large-scale effects of dark energy are summarized through the

A) local expansion rate, $\Omega$ .
B) cosmological constant, $\bigwedge$ .
C) Hubble constant, H₀.
D) amount of matter in the universe, $\Omega$ _m.
E) critical density, $\Omega$ ₀.

Question 19

Observations of Type Ia supernovae show that the redshifts of the most distant galaxies are ________ the value predicted by Hubble's Law.

A) the same as
B) less than
C) greater than
D) the reciprocal of
E) negative

Question 20

In a universe dominated by an accelerated expansion rate, the actual age of the universe is ________ the Hubble time.

A) older than
B) younger than
C) negligible compared with
D) the same as
E) independent of

Question 21

What evidence has been found to support the existence of an era of cosmological inflation?

A) Small fluctuations in the cosmic microwave background radiation.
B) This era has been directly observed beyond the cosmic microwave background radiation.
C) The variation in brightness of Type Ia supernovae provides indirect evidence for inflation.
D) Inflation is a result of extrapolating the currently measured changes in dark energy back in time.
E) An era of inflation solves several problems in cosmology, but no direct evidence of this era exists.

Question 22

The flatness problem arises because only a universe with a value of ________ can have that value forever and also contain matter.

A) ( $\Omega$ _m + $\Omega$ _$\bigwedge$ =0)
B) ( $\Omega$ _m + $\Omega$ _$\bigwedge$ =1)
C) ( $\Omega$ _m + $\Omega$ _$\bigwedge$ = 0.7)
D) ( $\Omega$ _m+ $\Omega$ _$\bigwedge$ =0.02)
E) ( $\Omega$ _m = $\Omega$ _$\bigwedge$ =0)

Question 23

The mechanism of ________ can simultaneously solve both the flatness and horizon problems in cosmology.

A) nucleosynthesis
B) quantum tunneling
C) TOE
D) inflation
E) dark energy

Question 24

Which of the fundamental forces in nature have an infinite range of action?

A) electromagnetic and gravity
B) strong nuclear and gravity
C) strong and weak nuclear
D) electromagnetic and strong nuclear
E) All four fundamental forces have an infinite range of action.

Question 25

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

A) 180 $\degree$ .
B) ( $\lt$ 180 $\degree$ .)
C) 120 $\degree$ .
D) ( $\gt$ 180 $\degree$ .)
E) 240 $\degree$ .

Question 26

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 27

The figure below shows five graphs of the scale factor of the universe as a function of time.Which of these graphs would occur for a universe with $\Omega$ _m = 1 and $\Omega$ _$\bigwedge$ = 0?

A) A
B) B
C) C
D) D
E) E

Question 28

In a scenario in which dark energy is changing significantly over time, which of the following outcomes are possible?

A) Big Crunch and Big Rip
B) Big Crunch and constant expansion
C) Big Rip and Big Freeze
D) Big Crunch and Big Freeze
E) Big Chill and Big Freeze

Question 29

Why is the smoothness of the cosmic microwave background radiation (CMB) considered a problem?

A) A smooth CMB implies that the expansion of the universe should be constant with time
B) Because a relatively smooth CMB implies the universe should be one gigantic galaxy, not many billions of billions of galaxies.
C) A universe this smooth should have matter spread out so evenly, that no stars or galaxies should be able to form.
D) Because two opposite sides of the universe could not have been in contact, and so should not have been able to reach similar temperatures.
E) A universe with a CMB this smooth should have ended in a Big Crunch by now.

Question 30

Why would it be very improbable for our universe to have $\Omega$ _m + $\Omega$ _$\bigwedge$ = 0.9?

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

Question 31

Which of the curves in the figure shown below would best describe the scenario of a Big Rip for the universe?

A) A
B) B
C) C
D) all three of them
E) none of them

Question 32

The figure below shows five possible graphs of the scale factor of the universe as a function of time.Which of these graphs represent our universe, where $\Omega$ _m = 0.3 and $\Omega$ _$\bigwedge$ =0.7?

A) A
B) B
C) C
D) D
E) E

Question 33

Select the true statement:

A) ( $\Omega$ _$\bigwedge$ makes the universe flatter, while $\Omega$ _m makes the universe less flat.)
B) ( $\Omega$ _$\bigwedge$ + $\Omega$ _m is much smaller than the critical density.)
C) ( $\Omega$ _m is very close to zero.)
D) ( $\Omega$ _$\bigwedge$ and $\Omega$ _m both affect the predictions about the fate and age of the universe.)
E) Current observational data seem to suggest that the universe is not flat.

Question 34

Which of the curves in the figure shown below would best describe the scenario of a Big Crunch for the universe?

A) A
B) B
C) C
D) all three of them
E) none of them

Question 35

The universe can be infinite in size for which large-scale geometries?

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

Question 36

Choose the correct statement about inflation.

A) It helps solve both the problems of the flatness of the universe and the smoothness of the cosmic background radiation.
B) It assumes that at some point in the future dark energy will decay and the universe will expand rapidly by a factor of 10³⁰.
C) When the universe was approximately 1 second old, its size grew by a factor of 10³⁰.
D) It is the best version for a TOE.
E) Scientists have obtained direct and undisputable observational evidence that inflation did occur.

Question 37

The figure below shows a graph of the scale factor, R_U, with time, for three different scenarios.The age of the universe is the difference between now and the time at which R_U is zero.Which curve illustrates a universe that is expanding at a constant rate?

A) A
B) B
C) C
D) All of these curves are valid for constantly-expanding universe.
E) None of these curves is valid for constantly-expanding universe.

Question 38

The figure below shows a graph of the scale factor, R_U, with time, for three different scenarios.The age of the universe is the difference between now and the time at which R_U is zero. Which curve illustrates an accelerating universe?

A) A
B) B
C) C
D) All of these curves are valid for an accelerating universe.
E) None of these curves is valid for an accelerating universe.

Question 39

Quantum chromodynamics (QCD) describes how ________ works.

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

Question 40

The figure below shows five graphs of the scale factor of the universe as a function of time.Which of these graphs would occur for a universe with $\Omega$ _m =1 and $\Omega$ _$\bigwedge$ = 0?

A) A
B) B
C) C
D) D
E) E

Question 41

Which fundamental force is responsible for radioactive beta decays?

A) electromagnetic
B) gravity
C) weak nuclear
D) photons
E) strong nuclear

Question 42

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 devoid of matter, entirely composed of photons.
E) It would look similar to our universe, but the charges of all of the particles would be reversed.

Question 43

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) the accelerating expansion of the universe.
E) what happens inside a black hole.

Question 44

Which fundamental force is responsible for chemistry and for holding solids together?

A) electromagnetic
B) gravity
C) weak nuclear
D) dark matter
E) strong nuclear

Question 45

Which of the four fundamental forces enables nuclear fusion inside stars?

A) electromagnetic
B) gravity
C) weak nuclear
D) magnetic
E) strong nuclear

Question 46

Which list correctly orders objects from the first one to form after the Big Bang to 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 47

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 from the single superforce
C) around the time the strong force separated from 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 48

Which of the following would represent the unification of all fundamental forces?

A) the electroweak theory
B) quantum chromodynamics (QCD)
C) quantum electrodynamics (QED)
D) grand unified theories (GUT)
E) the theory of everything (TOE)

Question 49

The figure below illustrates pair production in the early universe, with one particle labeled with a question mark.What type of particle must this be?

A) proton
B) electron
C) antiproton
D) positron
E) neutron

Question 50

Scientists think that, soon after the Big Bang, the four fundamental forces of nature were united into one "superforce," and ________ was the first to split off from the others.

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

Question 51

To verify whether 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 52

A grand unified theory (GUT) unites which forces?

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

Question 53

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

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

Question 54

What particles are the carriers of the electromagnetic force?

A) electrons
B) magnetic monopoles
C) gluons
D) photons
E) W ⁺

Question 55

Compared to an electron, the antiparticle of an electron has

A) the same charge but negative mass.
B) the same mass but opposite charge.
C) opposite charge and higher mass.
D) the same charge and higher mass.
E) opposite charge and negative mass.

Question 56

Which of the four fundamental forces is the weakest?

A) electromagnetic
B) gravity
C) weak nuclear
D) magnetic
E) strong nuclear

Question 57

What is the Planck era?

A) the earliest moments after the Big Bang
B) the current era of the universe
C) the era during which quantum forces evolved into their current form
D) the era during which inflation occurred
E) the era of human history during which Max Planck's theories dominated physics

Question 58

In the very early universe, which of the following types of particles and antiparticles first stopped being spontaneously formed out of photons and why?

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 59

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 CMB.
E) QED combined the electric and magnetic forces.

Question 60

What fundamental force is responsible for holding the nucleons together inside atomic nuclei?

A) electromagnetic
B) gravity
C) weak nuclear
D) dark energy
E) strong nuclear

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 that 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 roll of dice
D) a multiverse with constant inflation, where each universe forms due to quantum fluctuations stopping that inflation
E) all of these

Question 62

In the string theory that could successfully unite 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) eleven dimensions (10 spatial and 1 temporal).

Question 63

In a universe with no dark energy, what will happen to the expansion of the universe in the future if (a) $\Omega$ _m $\gt$ 1, (b) $\Omega$ _m =1, and (c) $\Omega$ _m $\lt$ 1?

Question 64

Describe two different experiments that offer evidence for a flat universe.

Question 65

Which of the following have both been predicted and conclusively confirmed experimentally?

A) the decay of protons
B) the inflationary model
C) the carrier particles for the force of gravity
D) the Higgs boson
E) the 10 spatial dimensions in superstring theory

Question 66

If someone says, "the laws of the universe must be right for us to exist, because we are here observing it," they are invoking the

A) cosmological principle.
B) anthropic principle.
C) theory of everything.
D) idea of multiverses.
E) grand unified theory.

Question 67

At what temperature would the peak wavelength of blackbody radiation correspond to electron-positron pair production? This would have been the lowest temperature in the early universe at which this effect was common.(Note that a photon's energy is equal to , the cosmic background at any point in time has a blackbody spectrum that peaks at a wavelength , and the mass of a single electron or positron is 9.11 *10^-31 kg.)

A) 2400 K
B) 420,000 K
C) 2.4 million K
D) 42 million K
E) 2.4 billion K

Question 68

What would be the eventual state of the universe if the mass density $\Omega$ = $\Omega$ ₀, and dark energy did not exist?

Question 69

Superstring theory is a candidate for a(n)

A) infinite number of multiverses.
B) theory of everything.
C) theory describing the era prior to the Big Bang.
D) more fundamental theory of gravity, but ignores the other forces.
E) way to violate the cosmological principle.

Question 70

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

Question 71

The concept behind the possible existence of multiverses is that

A) if the universe has infinite space dimensions, then many nearly identical universes may be "stacked" in the dimensions that we cannot currently perceive.
B) if the cosmological principle does not hold at very large distances, then far outside our visible universe you might find places with laws of physics very different from our own.
C) if string theory is correct, then each "extra" dimension may actually be an entire separate universe.
D) fluctuations in the cosmic microwave background imply that some pockets of space should have different laws of physics than others.
E) there is no reasoning behind multiverses; they are a product of science fiction.

Question 72

The critical mass density of the universe today is 9.5 *10 ^{- 27} kg/m³.Using (only) the currently observed amount of luminous matter, what would be the average mass density in the universe? If protons 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 cubic root of the average volume occupied by one proton, and the mass of a proton is 1.67 *10 ^{- 27} kg.)

Question 73

How does the critical density, $\rho$ _c, depend on the observed value of the Hubble constant, H₀?

Question 74

Explain what it means for the universe to be accelerating.How does this compare with the use of the term acceleration in relation to the motion of a single object?

Question 75

Imagine that you lived in a universe where there is enough mass to slow the expansion rate of the universe.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.

Question 76

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 77

Explain, ignoring dark energy, how the figure below describes three different scenarios for the evolution of the universe.Be sure to explain the meaning of the scale factor, R_U.

Question 78

String theory is

A) a confirmed fact.
B) the correct theory, but we don't fully understand it, like gravity.
C) currently untestable.
D) experimentally verified, but the theory does not fully explain the evidence.
E) pure science fiction, with no grounding in science or mathematics.

Question 79

Briefly explain the possible scenarios for the fate of the universe assuming that: (a) dark energy decreases in time, (b) it increases in time, and (c) it is a constant.

Question 80

What is the minimum combined energy of the photons that would produce an electron-positron pair? (Note: m_e is the rest mass of an electron.)

A) 2m_ec²
B) m_ec²
C) 1/2m_ec²
D) m_e²c⁴
E) This cannot happen.