Question 1

The density of the Universe is

Accepted Answer

According to current measurements and observations, the Universe is flat, and its density is equal to the critical density. If the Universe were closed or open, its density would be greater or lower than the critical density, respectively.

Question 2

If galaxy A is four times more distant than galaxy B, then according to the Hubble law, galaxy A will recede ___________ than galaxy B.

Accepted Answer

The Hubble Law states that the recessional velocity of a galaxy is directly proportional to its distance from us. Therefore, if galaxy A is four times more distant than galaxy B, it will recede four times faster.

Question 3

Astronomers believe that the hydrogen atoms in your body were created

Accepted Answer

The big bang is the event that started the universe as we know it, and all the matter in the universe was created during this event. Therefore, the hydrogen atoms in our bodies (which make up a significant portion of our mass) were also created during the big bang.

Question 4

What observation has prompted astronomers to ponder the possible existence of dark energy

Accepted Answer

Observations of supernovae at large redshifts have shown that they appear fainter than expected, indicating that the expansion of the universe is accelerating. This suggests the existence of an unknown energy density, or "dark energy," which is thought to be responsible for this acceleration.

Question 5

Whether the Universe is open, closed or flat depends, on the ___________ of the Universe.

Accepted Answer

The curvature of space in the Universe is determined by its density. If the density is greater than the critical density, then the Universe is closed and has positive curvature. If the density is less than the critical density, then the Universe is open and has negative curvature. If the density is equal to the critical density, then the Universe is flat and has zero curvature.

Question 6

Where did the cosmic microwave background (CMB) come from

Accepted Answer

The cosmic microwave background (CMB) is the oldest light in the universe, dating back to about 380,000 years after the Big Bang. It was created when the universe cooled enough for electrons to combine with nuclei (mostly hydrogen and helium) to form atoms, which allowed photons to travel freely without scattering. These photons have been traveling through the universe ever since and have been redshifted to microwave wavelengths, which is why it is called the cosmic microwave background.

Question 7

Which of the following types of Universe has no center and no edge

Accepted Answer

All models of the universe, whether closed, flat, or open, are described by the theory of general relativity to have no center and no edge. This is because they are all considered to be infinite or unbounded in their own ways, making the concepts of a center or an edge not applicable.

Question 8

Current evidence suggests that the Universe is

Accepted Answer

Recent observations of distant supernovae and the cosmic microwave background radiation have provided strong evidence that the expansion of the universe is accelerating. This suggests that the Universe is flat and infinite, but not slowing down or contracting. Therefore, the best choice is E: flat, infinite, and accelerating in its expansion.

Question 9

Why is the cosmic microwave background (CMB) so cold if the early Universe was so hot

Accepted Answer

The expansion of the Universe has caused the wavelength of the photons in the CMB to stretch, or redshift, over time. This redshifting has resulted in a cooling of the CMB, even though the early Universe was much hotter.

Question 10

Possible equations (choose the correct one): $τ =10^{12}$/H; H=v/d. If gravity is unimportant and H equals 75 km/s/Mpc, then the age of the universe is about

Accepted Answer

First, we need to find the value of H in units of seconds. To do this, we can convert 1 Mpc (megaparsec) to km:

1 Mpc = 3.086 × 10^19 km

So:

H = 75 km/s/Mpc 
  = 75 km/s / (3.086 × 10^19 km/Mpc) 
  = 2.43 × 10^-18 s^-1

Next, we can use the equation H = v/d to solve for the age of the universe (τ), where v is the recessional velocity of distant galaxies and d is the distance to those galaxies. We'll assume v is equal to H times the distance to the galaxies (i.e. v = Hd) due to the expansion of the universe:

τ = 1/H 
  = 1/(2.43 × 10^-18 s^-1) 
  = 4.11 × 10^17 s 
  ≈ 13 billion years

So, the best choice is B, which is 13 billion years.

Question 11

Astronomers have found the center of the Universe to be located in

Accepted Answer

According to current understanding of cosmology, there is no single point in the Universe that serves as its center. The Universe is thought to be expanding uniformly in all directions, and as such, there is no privileged location that can be considered the center.

Question 12

How old is the Universe since the big bang Pick the best answer according to radioactive dating in the solar system, light travel times to most distant galaxies, time reversal of the big bang, and observations of the 3-K radiation.

Accepted Answer

The most accepted age of the Universe is 14,000,000,000 years based on various techniques used for determining its age, such as radioactive dating in the solar system, light travel times to the most distant galaxies, time reversal of the Big Bang, and observations of the 3-K radiation. This age is also supported by multiple lines of evidence from different branches of science.

Question 13

The flatness problem states that

Accepted Answer

The flatness problem refers to the fine-tuning required for the density of the Universe to be very close to the critical density. This is necessary for the geometry of the Universe to appear flat, as is observed, rather than curved or positively/negatively curved. Choice B and C are not correct because they describe scenarios where the density of the Universe is either much larger or much smaller than the critical density, which would not result in a flat geometry. Choices D and E are not correct because they suggest that the Universe has fewer dimensions than the observed 3D space.

Question 14

If a galaxy is located at a distance of 18 Mpc and is found to have recessional velocity of 1170 km/s, what is Hubble's constant based only on this galaxy

Accepted Answer

Hubble's constant is given by the ratio of the recessional velocity to the distance. In this case, the recessional velocity is 1170 km/s and the distance is 18 Mpc. Therefore, Hubble's constant is 1170 km/s / 18 Mpc = 65 km/s/Mpc.

Question 15

Evidence for a very early "super rapid" inflation of the universe is that the 3-K radiation from opposite sides of the sky (i.e., 180 degrees or about 28 billion light years apart) is of nearly ___________ intensity. Time for light to travel this distance is ___________ the age of the universe in years.

Accepted Answer

The nearly equal intensity of the 3-K radiation from opposite sides of the sky suggests that those regions were once in contact, but were separated by a rapid expansion. This rapid expansion is believed to be the result of super rapid inflation of the universe. The time for light to travel this distance is greater than the age of the universe, which is believed to be around 13.8 billion years.

Question 16

One explanation of the dark sky Olbers's Paradox is that light can reach us only from objects in space out to a distance in light years _______ the age of the universe in years.

Accepted Answer

The correct explanation is that the observable universe is limited to regions from which light has had enough time to reach us since the beginning of the universe. Therefore, we can only see objects from which light has traveled a distance less than or equal to the age of the universe in light years.

Question 17

What observational evidence supports the fact that our universe is static and unchanging

Accepted Answer

The observational evidence listed (A, B, C, D) actually supports the fact that our universe is not static and unchanging. The cosmic microwave background (A) is evidence of the Big Bang and the universe's evolution from a hot, dense state. The dark sky at night (B), or Olbers' paradox, suggests the universe is not infinite and unchanging. The redshift of galaxies (C) indicates that the universe is expanding, and the evolution of galaxies with distance (D) shows that the universe has changed over time. Therefore, none of the choices support a static and unchanging universe.

Question 18

The flatness problem and horizon problem

Accepted Answer

The flatness problem and horizon problem can be solved by the theory of cosmic inflation, which suggests that there was a sudden, exponential expansion of the Universe at a time before recombination occurred. This rapid expansion would have smoothed out the curvature of the Universe and caused distant regions to be in thermal equilibrium, explaining the observed homogeneity and isotropy.

Question 19

Which of the following agrees with a no-center, no-edge Universe

Accepted Answer

The concept of a no-center, no-edge universe is compatible with all three geometries mentioned: flat, positive-curved (spherical), and negative-curved (hyperbolic). Each of these geometries describes a universe that is infinite or unbounded in such a way that it doesn't have a center or an edge, consistent with the principles of cosmology.

Question 20

"Seeds" around which galaxies, clusters and walls grew may have been ___________ before inflation and recombination.

Accepted Answer

The current scientific consensus is that the seeds around which galaxies, clusters, and walls grew were caused by initially tiny quantum mechanical fluctuations in space-time. These fluctuations were amplified by the rapid expansion of the Universe during inflation, which stretched these small perturbations into much larger scales, and eventually led to the formation of large-scale structure in the Universe.

Quiz 14: Modern Cosmology

The density of the Universe is

If galaxy A is four times more distant than galaxy B, then according to the Hubble law, galaxy A will recede ___________ than galaxy B.

Astronomers believe that the hydrogen atoms in your body were created

What observation has prompted astronomers to ponder the possible existence of dark energy

Whether the Universe is open, closed or flat depends, on the ___________ of the Universe.

Where did the cosmic microwave background (CMB) come from

Which of the following types of Universe has no center and no edge

Current evidence suggests that the Universe is

Why is the cosmic microwave background (CMB) so cold if the early Universe was so hot

Possible equations (choose the correct one) : $τ =10^{12}$ /H; H=v/d. If gravity is unimportant and H equals 75 km/s/Mpc, then the age of the universe is about

Astronomers have found the center of the Universe to be located in

How old is the Universe since the big bang Pick the best answer according to radioactive dating in the solar system, light travel times to most distant galaxies, time reversal of the big bang, and observations of the 3-K radiation.

The flatness problem states that

If a galaxy is located at a distance of 18 Mpc and is found to have recessional velocity of 1170 km/s, what is Hubble's constant based only on this galaxy

Evidence for a very early "super rapid" inflation of the universe is that the 3-K radiation from opposite sides of the sky (i.e., 180 degrees or about 28 billion light years apart) is of nearly _ intensity. Time for light to travel this distance is _ the age of the universe in years.

One explanation of the dark sky Olbers's Paradox is that light can reach us only from objects in space out to a distance in light years _______ the age of the universe in years.

What observational evidence supports the fact that our universe is static and unchanging

The flatness problem and horizon problem

Which of the following agrees with a no-center, no-edge Universe

"Seeds" around which galaxies, clusters and walls grew may have been ___________ before inflation and recombination.

Quiz 14: Modern Cosmology

The density of the Universe is

If galaxy A is four times more distant than galaxy B, then according to the Hubble law, galaxy A will recede ___________ than galaxy B.

Astronomers believe that the hydrogen atoms in your body were created

What observation has prompted astronomers to ponder the possible existence of dark energy

Whether the Universe is open, closed or flat depends, on the ___________ of the Universe.

Where did the cosmic microwave background (CMB) come from

Which of the following types of Universe has no center and no edge

Current evidence suggests that the Universe is

Why is the cosmic microwave background (CMB) so cold if the early Universe was so hot

Possible equations (choose the correct one) : τ=1012τ =10^{12}τ=1012 /H; H=v/d. If gravity is unimportant and H equals 75 km/s/Mpc, then the age of the universe is about

Astronomers have found the center of the Universe to be located in

How old is the Universe since the big bang Pick the best answer according to radioactive dating in the solar system, light travel times to most distant galaxies, time reversal of the big bang, and observations of the 3-K radiation.

The flatness problem states that

If a galaxy is located at a distance of 18 Mpc and is found to have recessional velocity of 1170 km/s, what is Hubble's constant based only on this galaxy

One explanation of the dark sky Olbers's Paradox is that light can reach us only from objects in space out to a distance in light years _______ the age of the universe in years.

What observational evidence supports the fact that our universe is static and unchanging

The flatness problem and horizon problem

Which of the following agrees with a no-center, no-edge Universe

"Seeds" around which galaxies, clusters and walls grew may have been ___________ before inflation and recombination.

Possible equations (choose the correct one) : $τ =10^{12}$ /H; H=v/d. If gravity is unimportant and H equals 75 km/s/Mpc, then the age of the universe is about