Question 1

Suppose we were to discover that the distances to other galaxies had all been overestimated by a factor of two.How would this discovery affect our estimate of the age of the universe?

Accepted Answer

The age of the universe is calculated based on the distance of other galaxies and how fast they are moving away from us, which is measured by their redshift. If the distances were half of what we thought, then the galaxies would appear to be moving away from us at half the rate we previously estimated. This means that the expansion of the universe would have started more recently, and thus the estimated age would be cut in half.

Question 2

An observer now located at a distance of 3 billion light years from us could look in our general direction and see

Accepted Answer

The Hubble's law states that galaxies are moving away from each other at a rate proportional to their distance. This relationship holds true regardless of the observer's location in the universe. Thus, an observer located 3 billion light years from us would still see the same Hubble's law that we observe from Earth. They would see galaxies farther away from us moving away at a faster rate than those closer to us, indicating an expanding universe.

Question 3

What produced the radiation that we see as the 3 degree background radiation?

Accepted Answer

The 3 degree background radiation is also known as the cosmic microwave background (CMB) radiation. It is believed to be the leftover heat from the Big Bang itself, as the universe rapidly expanded and cooled. The radiation is visible in all directions of the sky and corresponds to a temperature of approximately 2.7 Kelvin. Glowing gas from the early universe is responsible for producing this radiation.

Question 4

Which of the following is a statement of the cosmological principle?

Accepted Answer

The cosmological principle states that the universe looks the same (i.e. exhibits the same physical laws and structures) to all observers everywhere. Choice A is incorrect as the principle does not state that the universe has always looked the same. Choice C is incorrect as it pertains to stellar evolution rather than the behavior of the universe as a whole. Choice D is incorrect as it pertains to a specific cosmological model (the Big Crunch) rather than a general principle.

Question 5

Which statement is true of the cosmic background radiation?

Accepted Answer

The cosmic background radiation is greatly redshifted, indicating that it comes from a time when the universe was much hotter and denser, shortly after the Big Bang. This redshift is a result of the expansion of the universe.

Question 6

In a universe that is isotropic

Accepted Answer

In an isotropic universe, things would look the same in all directions, meaning the same structures and objects would be observed regardless of the direction of observation. This is a fundamental assumption of the current standard model of cosmology, where the universe is considered homogeneous and isotropic on large scales.

Question 7

If we were to discover that Hubble's constant is actually twice as large as it is now thought to be,how would that alter our estimate of the expansion age of the universe?

Accepted Answer

Hubble's constant is used to estimate the age of the universe based on the rate of expansion. If the constant were twice as large, that would mean the universe is expanding at a faster rate than we previously thought, which would mean it has taken less time to expand to its current size. Therefore, our estimate of the expansion age of the universe would be cut in half.

Question 8

Which of the following is true of the cosmic background radiation?

Accepted Answer

The cosmic background radiation was produced a few 100,000 years after the beginning of the expansion. This corresponds to the time when the Universe cooled down enough for neutral atoms to form, allowing photons to travel freely through space.

Option A is incorrect as the cosmic background radiation is isotropic, meaning it has the same intensity in all directions.

Option B is incorrect as the cosmic background radiation was not produced by stars but rather is a consequence of the early Universe's temperature and density fluctuations.

Option D is incorrect as the cosmic background radiation is in the microwave part of the spectrum, not the ultraviolet part.

Question 9

If the universe is flat,where is its center?

Accepted Answer

The universe being flat means that it has no curvature and therefore no center. As there is no point at which the curvature of the universe is equal in all directions, there is no way to locate a center. The universe is infinitely large and expands uniformly in all directions.

Question 10

In which part of the sky is the cosmic background radiation brightest?

Accepted Answer

The cosmic background radiation is believed to be uniformly distributed throughout the entire universe, which means it should be equally bright in all parts of the sky. This is because the radiation was emitted early in the universe's history, and has been traveling through space for roughly 13.8 billion years. As a result, it should be present in all directions, though it may appear slightly brighter or fainter in certain regions due to slight variations in temperature.

Question 11

The expansion age of the universe is about

Accepted Answer

According to the most widely accepted theories and observations, the expansion age of the universe is estimated to be around 13.8 billion years. Therefore, the best choice is B, which is the option closest to this value. Option C is too high, and options A and D are too low.

Question 12

Which of the following is NOT an implication of Hubble's law?

Accepted Answer

Hubble's law implies that the universe is expanding, which suggests that it had a beginning and was once denser than it now is. However, it does not imply that we are in the center of the universe. In fact, Hubble's law appears to imply that there is no center to the universe.

Question 13

The universe is generally assumed to be isotropic.What does "isotropic" mean?

Accepted Answer

Isotropic means that the universe has the same properties and appears the same in all directions. Therefore, choice A, which says the universe looks the same in all directions, is the best choice.

Question 14

Which of the following is true for a universe in which space is flat?

Accepted Answer

A flat universe has an infinite extent in all directions and no curvature, which means it would not have a center. If it had a center, it would show some curvature, so option A and C can be ruled out. Hence, option B is the correct answer. Option D is also incorrect since it implies that the universe has boundaries, which is not supported by observations.

Question 15

Which of the following is true of the universe if it is made of flat space?

Accepted Answer

If the universe is made of flat space, it means the geometry of the universe is flat and parallel lines will never meet. In this case, the universe would be infinite, with no boundaries or edges.

Question 16

Why is the cosmic background radiation found primarily in the radio part of the spectrum?

Accepted Answer

The cosmic background radiation is found primarily in the radio part of the spectrum because it is highly redshifted. The radiation was emitted about 380,000 years after the Big Bang, and as the universe expanded, the wavelengths of the radiation stretched out, causing the radiation to be redshifted into the radio part of the spectrum.

Question 17

In which part of the spectrum is the cosmic background radiation brightest?

Accepted Answer

The cosmic background radiation is in the microwave part of the spectrum and is brightest in the radio portion of this range. This radiation is actually the afterglow of the Big Bang and is present in all parts of the sky.

Question 18

Suppose our universe has negative curvature.Which of the following statements would be FALSE?

Accepted Answer

A universe with negative curvature is often described as being saddle-shaped or hyperbolic, implying it does not have a center. This characteristic is a property of the geometry of the space itself, not a physical location within that space.

Question 19

In which respect are flat and positively curved universes alike?

Accepted Answer

Both flat and positively curved universes lack a defined center, adhering to the principle of cosmological homogeneity and isotropy, which states that the universe is uniform and isotropic on large scales, without a central point.

Question 20

If the universe is closed,where is its center?

Accepted Answer

If the universe is closed, it would mean that space is curved in on itself, forming a three-dimensional sphere, much like the surface of a balloon. In such a scenario, there would be no center point that one could identify as the "center" of the universe.

Quiz 26: Cosmology