Question 1

Which of the following factors is the most important in determining whether universal expansion continues forever or collapses back onto itself?

Accepted Answer

The average density of the universe determines whether the gravitational attraction between matter will result in the universe slowing down and ultimately collapsing back onto itself, or if the expansion will continue forever. If the average density is above a certain value known as the critical density, then the universe will collapse. If it is below the critical density, then the expansion will continue forever. The other factors listed (total mass, average temperature, total size) can be important in understanding the nature and evolution of the universe, but do not have as direct an impact on its ultimate fate as density does.

Question 2

The four physical forces at work in the universe are gravitation,electromagnetic,strong nuclear,and weak nuclear forces.Which two of these are very short-ranged,extending over distances of only about 10-15 m?

Accepted Answer

The strong and weak nuclear forces are very short-ranged, acting over distances of about 10^-15 meters, which is roughly the scale of atomic nuclei. The strong nuclear force holds the nucleus together, while the weak nuclear force is responsible for certain types of radioactive decay.

Question 3

At the start of the Big Bang,all of the fundamental forces were unified and behaved like a single force.As the universe expanded and cooled during the Big Bang,which was the first force to "freeze out" as a separate force?

Accepted Answer

Gravity was the first force to separate from the unified force as the universe expanded and cooled. This separation marked the beginning of the differentiation of the fundamental forces into their distinct forms.

Question 4

Homogeneity means

Accepted Answer

Homogeneity refers to the property of the universe being uniform or the same in every region. This means that the large-scale structure of the universe looks the same regardless of where you look from. This is a fundamental assumption in modern cosmology and is supported by observational evidence such as the cosmic microwave background radiation. The other options, such as blueshift and redshift, acceleration, and looking the same in every direction are related to other important concepts in cosmology but do not specifically refer to homogeneity.

Question 5

What significant event occurred 380,000 years after the start of the Big Bang?

Accepted Answer

380,000 years after the start of the Big Bang is known as the recombination era, when the Universe had cooled enough for electrons and nuclei to combine and form neutral atoms. This was a significant event because it allowed radiation to travel freely through the Universe, leading to the formation of the cosmic microwave background radiation that we observe today.

Question 6

The physical force that controls the structure of the nucleus and binds together protons and neutrons is the

Accepted Answer

The strong nuclear force is the physical force that controls the structure of the nucleus and binds together protons and neutrons. It is much stronger than the electromagnetic force and the weak nuclear force, and is responsible for the stability of atomic nuclei. Gravitational force plays a negligible role in the structure of atomic nuclei.

Question 7

If the redshift of a galaxy is greater than another,it is also at a

Accepted Answer

According to Hubble's Law, the greater the redshift of a galaxy, the greater its distance from us. Therefore, the correct choice is D, greater distance.

Question 8

If space has a closed geometry,what will happen to two initially parallel flashlight beams as they traverse billions of light-years of space?

Accepted Answer

In a closed geometry, the universe is finite and has a curved shape like a hypersphere. As the two flashlights beams travel billions of light-years, they will gradually converge due to the curvature of space and eventually cross. This is because light follows the curvature of space and travels along a geodesic, which is a curved path in the curved space.

Question 9

In which order did the fundamental forces of nature "freeze out" of the initial phase of the Big Bang at the beginning of the universe?

Accepted Answer

Gravity separated first, followed by the strong force, and finally the weak force as the universe cooled from the Big Bang.

Question 10

Hubble found that the more distant a galaxy,the

Accepted Answer

Hubble's law states that the farther a galaxy is from us, the greater its redshift and the faster it is moving away from us due to the expansion of the universe. This relationship between distance and redshift is known as Hubble's law, which has been confirmed by numerous observations and is a cornerstone of modern cosmology.

Question 11

Isotropic means

Accepted Answer

Isotropic means looking the same in every direction.

Question 12

Penzias and Wilson were scientists who

Accepted Answer

Penzias and Wilson discovered the cosmic background radiation.

Question 13

Einstein's general theory of relativity suggests that

Accepted Answer

Einstein's general theory of relativity proposes that massive objects cause a distortion in the fabric of space-time, which we experience as gravity. This means that the path of light is bent by the curvature of space, and objects move along the curvatures in a way that explains the observed effects of gravity. Therefore, D is the correct choice. A is incorrect, as the universeshape is still under debate, and B and C are both concepts from special relativity, which is a separate theory from the general theory of relativity.

Question 14

If one galaxy is twice as far from Earth as another,its velocity will be

Accepted Answer

According to Hubble's Law, the velocity at which a galaxy is moving away from us is directly proportional to its distance from us. Therefore, if one galaxy is twice as far from Earth as another, its velocity will be twice as much.

Question 15

Why did Einstein introduce his cosmological constant into the original field equations for general relativity?

Accepted Answer

At the time when Einstein introduced his cosmological constant in 1917, the dominant view among physicists was that the universe was static, and there was no evidence to suggest otherwise. However, the original field equations of general relativity predicted an unstable universe that was either expanding or contracting. Einstein introduced the cosmological constant as a modification to these equations to allow for a stable, static universe. It was only later, with the discovery of the expansion of the universe by Edwin Hubble, that Einstein abandoned the cosmological constant and referred to it as his "greatest mistake."

Question 16

What solution has been proposed by cosmologists to explain the remarkable uniformity of temperature throughout our universe?

Accepted Answer

The proposed solution by cosmologists to explain the remarkable uniformity of temperature throughout our universe is a brief period of extremely rapid expansion of space by a very large factor, known as cosmic inflation. This theory suggests that the universe underwent a period of exponential expansion just fractions of a second after the big bang, causing it to become incredibly large and uniform in temperature.

Question 17

How do we know that matter in the early universe was extremely smooth (i.e. ,not really lumpy)?

Accepted Answer

The cosmic background radiation is almost completely isotropic, meaning that it has a very uniform temperature distribution. This indicates that matter in the early universe was also very smooth and uniform, with only slight fluctuations that led to the formation of galaxies and other structures over time.

Question 18

If space has an open geometry what will happen to two initially parallel flashlight beams as they traverse billions of light-years of space?

Accepted Answer

In an open geometry, the universe is negatively curved, causing initially parallel light beams to gradually diverge or move apart from each other as they travel through space.

Question 19

Which of the following statements correctly describes the universe for the entire first 380,000 years of its life?

Accepted Answer

For the first 380,000 years of its life, the universe was filled with ionized gas, which made it opaque to radiation. This means that light and other forms of electromagnetic radiation couldn't travel very far before being absorbed and re-emitted by the gas, so the universe was effectively "foggy" or "hazy". It wasn't until the universe cooled down enough for atoms to form (which happened around 380,000 years after the Big Bang) that the fog cleared and radiation could travel more freely.

Question 20

When we look out into the universe,far beyond the edges of our own local group of galaxies,we see objects traveling away from us equally in all directions.This shows that

Accepted Answer

The fact that objects are traveling away from us equally in all directions suggests that the expansion must be the same everywhere in the universe, as we cannot be at the exact center of the universe. If we were at the center, the expansion would appear to be happening in a directional bias.

Quiz 15: Observing the Evolution of the Universe