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7 Quiz

Answer the following questions in order to test your understanding of the key ideas that you have been learning about.

Question 1

The galaxy NGC1234 has a redshift of z = 0.0113. Assuming the Hubble constant is 67.7 km s-1 Mpc-1, what is the distance to NGC1234 (to 2 significant figures)?

 

Answer

The Hubble constant implies that the apparent recession speed of galaxies increases by 67.7 km s-1 for every increase in distance by 1 Mpc. Using Equation (1), cap d equals z times c solidus cap h sub zero equals left parenthesis 0.0113 multiplication 300 comma 000 km s super negative one right parenthesis solidus 67.7 km s super negative one Mpc super negative one, so D = 50 Mpc.

Question 2

Which of the following is the correct description for the expansion of the Universe?

 

Answer

Soon after the big bang, the expansion rate of the Universe decelerated because of the dominance of matter. About 6 billion years ago, dark energy came to dominate the Universe causing the expansion rate to accelerate.

Question 3

Which one of the following statements about the CMB is true?

 

Answer

Only the last statement is true.

Question 4

Which of the following statements about baryonic and non-baryonic matter are true?

 

Answer

All statements are true except the last one.

Question 5

Which is the correct order of contributions to the overall matter-energy density of the Universe from smallest to largest?

 

Answer

The correct order is baryonic matter (5%), dark matter (25%), dark energy (70%).

Question 6

Which values of the equation of state parameter are associated with each of the following types of fluid?

w equals zero

baryonic matter

w equals prefix plus of one solidus three

radiation

w equals negative one

cosmological constant

w equals w sub zero plus left parenthesis one minus a right parenthesis times w sub a

quintessence

Using the following two lists, match each numbered item with the correct letter.

  1. w equals zero

  2. w equals prefix plus of one solidus three

  3. w equals negative one

  4. w equals w sub zero plus left parenthesis one minus a right parenthesis times w sub a

  1. baryonic matter

  2. radiation

  3. cosmological constant

  4. quintessence

The correct answers are:
  • 1 =
  • 2 =
  • 3 =
  • 4 =

Answer

The equation of state parameter is zero for matter, minus one for a cosmological constant, +1/3 for radiation, and a function of the scale parameter for quintessence.

Question 7

Which of the following problems in cosmology cannot be solved by inflation?

 

Question 8

What type of curvature does the universe have for each of the following combinations of matter density (Ωm) and dark energy density (ΩΛ)? (Assume that only matter and dark energy are present in these hypothetical universes.)

flat

Ωm = 0.25, ΩΛ = 0.75

negative

Ωm = 0.05, ΩΛ = 0.50

positive

Ωm = 0.65, ΩΛ = 0.65

Using the following two lists, match each numbered item with the correct letter.

  1. flat

  2. negative

  3. positive

  1. Ωm = 0.25, ΩΛ = 0.75

  2. Ωm = 0.05, ΩΛ = 0.50

  3. Ωm = 0.65, ΩΛ = 0.65

The correct answers are:
  • 1 =
  • 2 =
  • 3 =

Answer

If Ωm + ΩΛ > 1, the universe has positive curvature; if Ωm + ΩΛ < 1, the universe has negative curvature; and if Ωm + ΩΛ = 1, the universe is flat.

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OpenLearn - Unsolved problems in cosmology
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