Deck 21: Modern Cosmology

Question 1

The critical density of the universe is approximately equal to

A) .
B) .
C) .
D) .

Answer 1

.

Question 2

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

Answer 2

False

Question 3

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.

Answer 3

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

Question 4

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

Question 5

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

Question 6

Astronomers have confirmed the grand unified theory by observing that protons decay in laboratory experiments.

Question 7

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

Question 8

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 9

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

A) , .
B) , , .
C) , , .
D) , , .

Question 10

During inflation when the universe was approximately 1 second old,its size grew by a factor of .

Question 11

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

Question 12

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

Question 13

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

Question 14

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

Question 15

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

Question 16

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

Question 17

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

Question 18

The fact that is very close to 1 means that its value has always been very close to 1.

Question 19

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

Question 20

If 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.

Question 21

In order to produce an electron and a positron,a photon must have

A) .
B) .
C) .
D) an infinite energy.

Question 22

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

A) GUTs
B) Quantum mechanics
C) Inflation
D) Dark energy

Question 23

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

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

Question 24

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

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

Question 25

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

A) Open
B) Closed
C) Flat
D) Open and flat

Question 26

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

Question 27

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

A)
B)
C)
D)

Question 28

Inflation happened

A) when the universe was s old.
B) when the universe expanded by a factor of approximately .
C) when the average energy of the vacuum of spacetime changed.
D) All of the above

Question 29

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

A) 180 degrees.
B) < 180 degrees.
C) > 180 degrees.
D) 240 degrees.

Question 30

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

A) Photons
B) Gluons
C) Quarks
D) W+ particles

Question 31

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.

Question 32

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.

Question 33

How does the addition of a nonzero cosmological constant 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 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.

Question 34

Is Einstein's "biggest blunder" still considered a mistake?

A) No,the cosmological constant is nonzero.
B) Yes,the cosmological constant turned out to be zero.
C) Somewhat,because he could have predicted that the universe was expanding even before Hubble observed it.
D) Both a and c are correct.

Question 35

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) All of the above

Question 36

Due to the fact that we live 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) the same as
D) independent of

Question 37

How would astronomers describe the antiparticle of an electron?

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

Question 38

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.

Question 39

If today and dark energy was a cosmological constant,the universe will

A) expand forever.
B) slow its expansion but never reverse it.
C) stop expanding and eventually collapse.
D) oscillate between expansion and collapse.

Question 40

Why would it be very improbable for our universe to have ?

A) It would quickly evolve to have a much different value of .
B) In order to exist,every universe must have .
C) We know ,based on the average density of galaxies.
D) The fluctuation in the CBR tell us that .

Question 41

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

A) 11 dimensions (10 spatial and 1 temporal).
B) 4 dimensions (3 spatial and 1 temporal).
C) 9 dimensions (8 spatial and 1 temporal).
D) 6 dimensions (3 spatial and 3 temporal).

Question 42

What will happen to the expansion of the universe in the future if: ,and ?

Question 43

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) gravity
D) nucleosynthesis

Question 44

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

Question 45

When the universe was __________ old,approximately 24 percent of the normal matter in it had been turned into helium.

A) 5 minutes
B) 8 hours
C) 1,000 years
D) 4.5 billion years

Question 46

What was the temperature of the universe when a typical CBR photon was no longer able to spontaneously create an electron and positron pair? Note that a photon has an energy equal to the CBR at any point in time has a blackbody spectrum that peaks at ,and the mass of a single electron is .

A) 2,000 K
B) 400,000 K
C) 4 million K
D) 2 billion K

Question 47

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 seven spatial dimensions are tightly wrapped around each other and have not expanded.
B) The other nine spatial dimensions are too small to be noticeable.
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.

Question 48

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 energy in the CBR 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.

Question 49

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

Question 50

By the time the universe was 5 minutes old,approximately 24 percent of the normal matter in it had been turned into

A) protons.
B) neutrons.
C) hydrogen.
D) helium.

Question 51

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 energy.

Question 52

A grand unified theory unites which forces?

A) Only electromagnetism,weak nuclear,and strong nuclear
B) Only gravity and strong nuclear
C) Only electromagnetism,gravity,and weak nuclear
D) All four known forces

Question 53

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

A) when galaxies were first formed.
B) when hydrogen and helium were formed.
C) when gravity was quantum mechanical.
D) the time of recombination.

Question 54

Grand unified theories are very attractive because they can explain

A) why the universe consists mostly of matter.
B) why the Big Bang never made any antimatter.
C) why we have five fundamental forces in the universe today.
D) why the CBR is very smooth.

Question 55

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 56

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 theory of everything
C) Around the time the strong force separated out of the grand unified theory
D) Around the time the weak force and electromagnetism separated

Question 57

What are two observations that when combined tell us that the universe has and is flat?

Question 58

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

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

Question 59

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 strong force
D) The weak force

Question 60

The critical mass density of the universe today is .Using the current observed value of ,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 mass of the proton is .

Question 61

What was the temperature of the universe when a typical CBR photon was no longer able to spontaneously create a proton and antiproton pair? Note that a photon has an energy equal to ,the CBR at any point in time has a blackbody spectrum that peaks at ,and the mass of a single proton is .

Question 62

Explain why astronomers cannot accurately model the exact history of the universe in the first few fractions of a second after the Big Bang?

Question 63

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

Question 64

In quantum electrodynamics (QED),what mediates the electromagnetic force between particles?

Question 65

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

Question 66

According to superstring theory,how are different varieties of elementary particles similar? How do they differ?

Question 67

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

Question 68

What is the difference between a grand unified theory and a theory of everything?

Question 69

What is the "flatness problem" in cosmology?

Question 70

What is the name of the particle that mediates the electromagnetic force in quantum electrodynamics (QED)and the strong force in quantum chromodynamics (QCD)?