Question 1

Briefly explain how Hubble's discovery of a relationship between galactic distance and redshift led to the idea of the Big Bang. (Hint: review chapter 16)

Accepted Answer

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Question 2

Rank these times based on the wavelength of the peak intensity of the cosmic background radiation at those times, from shortest to longest. (Hint: consider how the temperature of the universe or the cosmic background radiation changed with time.)
A)100 million years after the Big Bang, 1 million years after the Big Bang, today
B)today, 100 million years after the Big Bang, 1 million years after the Big Bang
C)1 million years after the Big Bang, 100 million years after the Big Bang, today
D)today, 1 million years after the Big Bang, 100 million years after the Big Bang

Accepted Answer

The peak intensity of the cosmic background radiation corresponds to a certain wavelength, which is determined by the temperature of the universe at that time. As the universe cools down, the peak intensity moves to longer wavelengths (or lower frequencies). Therefore, the earlier the time, the shorter the wavelength of the peak intensity. According to the Big Bang theory, the universe was much hotter and denser in the past, so the temperature was higher and the peak intensity was at shorter wavelengths. Among the given options, choice C is the correct ranking, with 1 million years after the Big Bang having the shortest wavelength, followed by 100 million years after the Big Bang, and then today, which has the longest wavelength.

Question 3

Which of the following is not an observed characteristic of the cosmic microwave background?
A)It has a perfect thermal radiation spectrum.
B)It contains prominent spectral lines of hydrogen, the primary chemical ingredient of the universe.
C)Its temperature is a little less than 3 Kelvin (3 degrees above absolute zero).
D)Its temperature is the same everywhere, except for small variations at the level of 1 part in 100,000.

Accepted Answer

The cosmic microwave background does not contain prominent spectral lines of hydrogen. Rather, it has a smooth, featureless spectrum.

Question 4

Why did the era of nucleosynthesis end?
A)Too many heavy elements were produced.
B)The temperature of the universe became too low.
C)Neutrinos carried off too much energy.
D)The density of the universe became too low.

Accepted Answer

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A)Too...

Question 5

Which of the following observations cannot be explained by the Big Bang theory unless we assume that an episode of inflation occurred?
A)the fact that the universe is expanding
B)the fact that the temperature of the cosmic microwave background is almost the same everywhere
C)the existence of the cosmic microwave background
D)the fact that about 25% of the ordinary matter in the universe consists of helium

Accepted Answer

The Big Bang theory explains the expansion of the universe, the existence of the cosmic microwave background, and the abundance of helium. However, the nearly uniform temperature of the cosmic microwave background across vast regions of space is best explained by the theory of inflation, which posits a rapid expansion of the universe shortly after the Big Bang. This rapid expansion would make the universe look the same in all directions (homogeneous and isotropic) at large scales, explaining the uniform temperature observed today.

Question 6

Why is the era of nucleosynthesis so important in determining the chemical composition of the universe?

Accepted Answer

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Question 7

In stars, helium can sometimes be fused into carbon and heavier elements (in their final stages of life). Why didn't the same fusion processes produce carbon and heavier elements in the early universe?
A)Temperatures in the early universe were never above the roughly 100 million Kelvin required for helium fusion.
B)Helium fusion occurred, but the carbon nuclei that were made were later destroyed by the intense radiation in the early universe.
C)By the time stable helium nuclei had formed, the temperature and density had already dropped too low for helium fusion to occur.
D)No one knows-this is one of the major mysteries in astronomy.

Accepted Answer

By the time stable helium nuclei had formed, the temperature and density had already dropped too low for helium fusion to occur.

Question 8

What happens when a particle of matter meets its corresponding antiparticle of antimatter?
A)They fuse to make a heavier particle.
B)They can form a complete atom.
C)The question makes no sense, since antimatter does not really exist.
D)The combined mass of the two particles is completely transformed into energy (photons).

Accepted Answer

When a particle of matter meets its corresponding antiparticle of antimatter, they annihilate each other and the combined mass of the two particles is completely transformed into energy (photons) according to Einstein's famous equation, E=mc². This process is known as annihilation.

Question 9

Evidence that the cosmic background radiation is the remnant of a Big Bang comes from predicting characteristics of remnant radiation from the Big Bang theory and comparing these predictions with observations. Four of the five statements below are real. Which one is fictitious?
A)The cosmic background radiation is expected to have a perfect thermal spectrum, and observations from the COBE spacecraft verify this prediction.
B)The cosmic background radiation is expected to have a temperature just a few degrees above absolute zero, and its actual temperature turns out to be 2.73 K.
C)The cosmic background radiation is expected to look essentially the same in all directions, and it does.
D)The cosmic background radiation is expected to contain redshifted emission lines from hydrogen and helium, and it does.
E)The cosmic background radiation is expected to have tiny temperature fluctuations at the level of about 1 part in 100,000. Such fluctuations were found in the COBE data.

Accepted Answer

There are indeed redshifted emission lines in the cosmic background radiation, but they come from earlier stars and galaxies rather than hydrogen and helium as the fictitious statement suggests.

Question 10

Why is the nucleosynthesis era so important in determining the chemical composition of the universe?
A)All the elements except hydrogen were produced in the nucleosynthesis era.
B)We can study the processes that occurred during the nucleosynthesis era to determine how most of the elements in the universe were created.
C)We can observe spectra from this era to determine what the primordial mix of the elements was at the beginning of the universe.
D)Except for a small amount of elements heavier than helium produced later by stars, the chemical composition of the universe is the same now as at the end of the nucleosynthesis era.
E)By knowing how much matter was created during the nucleosynthesis era, we can determine whether the universe is open or closed.

Accepted Answer

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Question 11

(From a science quiz that appeared in the weekly magazine The Economist.)Economic history is easier to write than the history of the universe. Nevertheless, most cosmologists now think that when the universe was formed,
A)first there was inflation, which caused the Big Bang, then recession.
B)first there was a Big Bang and then inflation (of space)which caused recession (of all matter, away from the Big Bang).
C)first there was a Big Bang. There has not been any inflation yet, but if it comes it will cause recession.

Accepted Answer

This choice accurately reflects the current understanding of cosmologists, who believe that the universe began with a Big Bang and then underwent a period of inflation which caused the rapid expansion of space. As the universe continued to expand, matter began to move away from the original point of the Big Bang, resulting in recession. Option A is incorrect, as inflation is believed to have occurred after the Big Bang, not before it. Option C is also incorrect, as there is evidence of inflation occurring soon after the Big Bang.

Question 12

In order for the cosmic microwave background to show hydrogen absorption lines at the redshift corresponding to the universe's age of 380,000 years, what condition would have been necessary?
A)There would have needed to be ionized hydrogen (which would contradict the idea that the CMB originates at the time the universe cooled enough for protons and electrons to combine, making neutral atoms).
B)There would have needed to be cooler hydrogen clouds (which would contradict the observation of a uniform temperature in all directions).
C)There would have needed to be even warmer hydrogen clouds (which would contradict the observation of a uniform temperature in all directions).

Accepted Answer

For hydrogen absorption lines to appear, there would need to be cooler hydrogen clouds to absorb the CMB radiation, which contradicts the observed uniform temperature of the CMB.

Question 13

Which of the following statements best explains what we mean when we say that the electroweak and strong forces "froze out" at 10- 38 second after the Big Bang?
A)Following this time, neither the strong nor electroweak forces were ever important in the universe again.
B)These forces are important only at temperatures below the freezing point of water-a temperature that the universe reached at an age of about at 10- 38 second.
C)Freezing out was a term coined by particle physicists who think that the Big Bang theory is really cool.
D)These two forces first became distinct at this time.

Accepted Answer

At 10-38 second after the Big Bang, the temperature of the universe was so high that the electroweak and strong forces were not distinct from each other. As the universe expanded and cooled, these two forces separated and became distinct, which is known as the "freezing out" of these forces. Therefore, option D, "These two forces first became distinct at this time," best explains what we mean when we say that the electroweak and strong forces "froze out" at 10-38 second after the Big Bang.

Question 14

Briefly explain why radiation was trapped for 380,000 years during the era of nuclei, and why the cosmic background radiation was formed at the end of this era.

Accepted Answer

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Question 15

The Big Bang theory is supported by two major lines of evidence that alternative models have not successfully explained. What are they?
A)(1)The theory predicts the existence of and the specific characteristics of the observed cosmic microwave background; (2)the theory correctly predicts the observed overall chemical composition of the universe.
B)(1)The theory correctly predicts that the universe should be expanding; (2)the theory predicts the existence of and the specific characteristics of the observed cosmic microwave background.
C)(1)The theory predicts the episode of inflation that we think occurred in the early universe; (2)the theory predicts the existence of large quantities of dark matter.
D)(1)The theory correctly predicts that the universe should be expanding; (2)the theory correctly predicts the observed ratio of spiral to elliptical galaxies in the universe.

Accepted Answer

The Big Bang theory is supported by two major lines of evidence that alternative models have not successfully explained: (1) the theory predicts the existence of and the specific characteristics of the observed cosmic microwave background; (2) the theory correctly predicts the observed overall chemical composition of the universe.

Question 16

Briefly describe one of the three questions left unanswered by the standard Big Bang theory which are solved by inflation. That is, describe either the structure problem, the uniformity (or smoothness)problem, or the density (or flatness)problem.

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Question 17

What is the Big Bang theory?
A)the idea that the universe as we see it formed when two massive galaxies collided together
B)the idea that the galaxy formed from the supernova explosion of a massive star
C)the idea that all matter and energy in the universe began in an unimaginably dense state, and then space itself began expanding

Accepted Answer

The Big Bang theory is the idea that all matter and energy in the universe began in an unimaginably dense state, and then space itself began expanding.

Question 18

Briefly describe the two key pieces of evidence that support the Big Bang theory.

Accepted Answer

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Question 19

This figure shows the temperature of the universe over time, according to models of the Big Bang. At what age did the universe cool to 1 million degrees?
A)about 1 second after the Big Bang
B)about 1015 seconds after the Big Bang
C)about 10- 3 seconds after the Big Bang
D)about 107 seconds after the Big Bang

Accepted Answer

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Question 20

What did the COBE satellite find regarding the smoothness of the cosmic background radiation?

Accepted Answer

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Quiz 17: The Birth of the Universe

Briefly explain how Hubble's discovery of a relationship between galactic distance and redshift led to the idea of the Big Bang. (Hint: review chapter 16)

Rank these times based on the wavelength of the peak intensity of the cosmic background radiation at those times, from shortest to longest. (Hint: consider how the temperature of the universe or the cosmic background radiation changed with time.)

Which of the following is not an observed characteristic of the cosmic microwave background?

Why did the era of nucleosynthesis end?

Which of the following observations cannot be explained by the Big Bang theory unless we assume that an episode of inflation occurred?

Why is the era of nucleosynthesis so important in determining the chemical composition of the universe?

In stars, helium can sometimes be fused into carbon and heavier elements (in their final stages of life) . Why didn't the same fusion processes produce carbon and heavier elements in the early universe?

What happens when a particle of matter meets its corresponding antiparticle of antimatter?

Evidence that the cosmic background radiation is the remnant of a Big Bang comes from predicting characteristics of remnant radiation from the Big Bang theory and comparing these predictions with observations. Four of the five statements below are real. Which one is fictitious?

Why is the nucleosynthesis era so important in determining the chemical composition of the universe?

(From a science quiz that appeared in the weekly magazine The Economist.) Economic history is easier to write than the history of the universe. Nevertheless, most cosmologists now think that when the universe was formed,

In order for the cosmic microwave background to show hydrogen absorption lines at the redshift corresponding to the universe's age of 380,000 years, what condition would have been necessary?

Which of the following statements best explains what we mean when we say that the electroweak and strong forces "froze out" at 10- 38 second after the Big Bang?

Briefly explain why radiation was trapped for 380,000 years during the era of nuclei, and why the cosmic background radiation was formed at the end of this era.

The Big Bang theory is supported by two major lines of evidence that alternative models have not successfully explained. What are they?

Briefly describe one of the three questions left unanswered by the standard Big Bang theory which are solved by inflation. That is, describe either the structure problem, the uniformity (or smoothness)problem, or the density (or flatness)problem.

What is the Big Bang theory?

Briefly describe the two key pieces of evidence that support the Big Bang theory.

This figure shows the temperature of the universe over time, according to models of the Big Bang. At what age did the universe cool to 1 million degrees?

What did the COBE satellite find regarding the smoothness of the cosmic background radiation?