Question 1

How long after the Big Bang was the Planck time, the time at which our current theories become completely unable to describe conditions any earlier in the universe?
A) 10⁻¹⁰ seconds
B) 10⁻³⁵ seconds
C) 10⁻⁴³ seconds
D) 3 minutes
E) 380,000 years

Accepted Answer

The Planck time is approximately 10⁻⁴³ seconds after the Big Bang, marking the earliest time at which our current physical theories can describe the universe.

Question 2

Why did the era of nuclei end when the universe was about 380,000 years old?
A) All the free particles had combined to form the nuclei of atoms.
B) The universe had expanded and cooled enough for stable, neutral atoms to form.
C) Atomic nuclei were finally able to escape the plasma of the early universe.
D) Photons were finally able to escape the plasma of the early universe and were no longer available to produce hydrogen and helium nuclei.
E) The nucleosynthesis era that produced the nuclei heavier than helium ended.

Accepted Answer

At the time when the universe was about 380,000 years old, the temperature had cooled enough for protons and electrons to combine to form neutral atoms. Prior to this, the free electrons scattered photons preventing them from traveling freely. But once the neutral atoms formed, the photons were able to travel unimpeded creating the Cosmic Microwave Background radiation. This marks the end of the era of nuclei.

Question 3

From what cosmic epoch do the photons in the cosmic background radiation originate?
A) the moment of the Big Bang
B) the end of the Planck era
C) during the era of nucleosynthesis
D) the end of the era of nuclei
E) during the era of galaxy formation

Accepted Answer

The photons in the cosmic background radiation originate from the end of the era of nuclei, also known as the recombination era, when electrons combined with protons to form neutral hydrogen atoms, allowing photons to travel freely through space.

Question 4

(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 a Big Bang and then inflation (of space) which caused recession (of all matter, away from the Big Bang).
B) first there was inflation, which caused the Big Bang, then recession.
C) first there was a Big Bang. There has not been any inflation yet, but if it comes it will cause recession.

Accepted Answer

The most widely accepted theory among cosmologists is that the universe started with a Big Bang, followed by a period of inflation where space expanded rapidly, causing all matter to recede away from the Big Bang. This theory is supported by observations such as the cosmic microwave background radiation and the large-scale structure of the universe. Option B is not supported by observations and is less widely accepted, while option C is not a valid explanation according to current theories.

Question 5

Why does the Big Bang theory predict that the cosmic background radiation should have a perfect thermal radiation spectrum?
A) The background radiation came from the heat of the universe, with a peak corresponding to the temperature of the universe.
B) The spectrum of pure hydrogen gas must be a perfect thermal radiation spectrum.
C) The spectrum of 75 percent hydrogen and 25 percent helium must be a perfect thermal radiation spectrum.
D) The light from all the stars and gas in the sky averaged over the entire universe will be a perfect thermal radiation spectrum.
E) It doesn't predict that the cosmic background radiation should have a perfect thermal radiation spectrum.

Accepted Answer

According to the Big Bang Theory, the cosmic background radiation is the afterglow of the hot, dense early universe that was filled with photons. As the universe expanded and cooled, these photons lost energy and their wavelengths stretched, ultimately reaching the microwave region of the electromagnetic spectrum. The cosmic background radiation should be a perfect thermal radiation spectrum because it originated from the heat of the early universe, with a peak corresponding to the temperature of the universe at that time.

Question 6

What kinds of atomic nuclei formed during the nucleosynthesis era?
A) only hydrogen
B) only helium
C) hydrogen, helium and trace amounts of lithium, beryllium, and boron
D) roughly equal amounts of hydrogen, helium, lithium, beryllium, and boron
E) essentially all of the chemical elements, except for those heavier than uranium

Accepted Answer

During the nucleosynthesis era, hydrogen, helium and trace amounts of lithium, beryllium, and boron were formed through fusion reactions in the early universe. The heavier elements were formed through nucleosynthesis in later generations of stars.

Question 7

Which forces have physicists shown to be the same force under conditions of very high temperature, as confirmed by experiments in particle accelerators?
A) gravity and the weak force
B) gravity and the strong force
C) the strong and weak forces
D) the strong and electromagnetic forces
E) the electromagnetic and weak forces

Accepted Answer

The electromagnetic and weak forces have been unified into the electroweak force, a concept confirmed by experiments in particle accelerators.

Question 8

What direct evidence do we have that the weak and electromagnetic forces were once unified as a single force?
A) The most advanced telescopes are able to see back to the GUT era in the universe.
B) Detectors on Earth have received photons and high-energy particles from the GUT era.
C) Temperatures in the center of the Sun can reproduce the conditions during the Electroweak era.
D) Particle accelerators on Earth can reach energies equivalent to the high temperatures of the Electroweak era and have produced particles predicted by the unified theory.
E) We have no direct evidence of such a unified force.

Accepted Answer

Particle accelerators on Earth, such as the Large Hadron Collider (LHC), can reach energies equivalent to the high temperatures present during the Electroweak era. These accelerators have produced particles predicted by the unified theory, providing direct evidence for the unification of the weak and electromagnetic forces.

Question 9

A GUT (grand unified theory) refers to theories that
A) unify all four forces.
B) unify gravity and the electromagnetic and weak forces.
C) unify gravity and the strong and weak forces.
D) unify the strong force and the electromagnetic and weak forces.
E) unify the electromagnetic and weak forces.

Accepted Answer

A Grand Unified Theory (GUT) aims to unify the strong force with the electromagnetic and weak forces, but does not include gravity.

Question 10

Why can't current theories describe what happened during the Planck era?
A) We do not yet have a theory that links quantum mechanics and general relativity.
B) We do not understand the properties of the antimatter that would have been produced at this time.
C) We do not yet have a theory that links the weak and electromagnetic forces.
D) We do not yet have a theory that explains how the universe underwent a rapid period of inflationary expansion.
E) The Planck era was the time before the Big Bang, and we cannot describe what happened before the beginning of the universe.

Accepted Answer

Current theories of physics cannot explain what happened during the Planck era because we do not yet have a theory that links quantum mechanics and general relativity. The laws of physics as we currently understand them break down at the incredibly high energies of the Planck era, and a unified theory that can describe the behavior of matter at such extreme conditions is still being sought.

Question 11

How many forces operated in the universe during the GUT era?
A) One: a single, symmetric "super force"
B) Two: gravity and the GUT force
C) Two: gravity and the electroweak force
D) Three: gravity, the strong force, and the electroweak force
E) All four of the known forces

Accepted Answer

During the GUT (Grand Unified Theory) era, it is theorized that there were two forces: gravity, which had already separated from the unified forces, and the GUT force, which later differentiated into the strong force, weak force, and electromagnetic force as the universe cooled.

Question 12

Which of the following statements about the cosmic background radiation is not true?
A) It has a temperature of about 3 degrees K above absolute zero.
B) It is the result of a mixture of radiation from many independent sources, such as stars and galaxies that formed within the first billion years of the Big Bang.
C) It had a much higher temperature in the past.
D) It was discovered by Penzias and Wilson in the mid 1960s.
E) It appears essentially the same in all directions (it is isotropic).

Accepted Answer

The cosmic background radiation is not the result of a mixture of radiation from many independent sources, as stated in choice B. Rather, it is the remnant radiation left over from the Big Bang itself. The other statements are true: the temperature is about 3 degrees K above absolute zero, it had a much higher temperature in the past, it was discovered by Penzias and Wilson in the mid 1960s, and it appears essentially the same in all directions (it is isotropic).

Question 13

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 observe spectra from this era to determine what the primordial mix of the elements was at the beginning of the universe.
C) 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.
D) We can study the processes that occurred during the nucleosynthesis era to determine how most of the elements in the universe were created.
E) By knowing how much matter was created during the nucleosynthesis era, we can determine whether the universe is open or closed.

Accepted Answer

The nucleosynthesis era is crucial because it set the initial abundances of light elements like hydrogen, helium, and small amounts of lithium and beryllium. The chemical composition of the universe has remained largely unchanged since then, except for heavier elements formed in stars.

Question 14

Approximately how long did the nucleosynthesis era last?
A) 10⁻¹⁰ seconds
B) 0.001 seconds
C) 5 seconds
D) 5 minutes
E) 5 years

Accepted Answer

The nucleosynthesis era, during which the first atomic nuclei formed, lasted for about 3 to 20 minutes after the Big Bang, making 5 minutes the closest approximation.

Question 15

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 temperature just a few degrees above absolute zero, and its actual temperature turns out to be 2.73 K.
B) The cosmic background radiation is expected to have a perfect thermal spectrum, and observations from the COBE spacecraft verify this prediction.
C) The cosmic background radiation is expected to contain redshifted emission lines from hydrogen and helium, and it does.
D) The cosmic background radiation is expected to look essentially the same in all directions, 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

The cosmic background radiation does not contain redshifted emission lines from hydrogen and helium; it is a nearly uniform thermal radiation with a blackbody spectrum.

Question 16

We have direct experimental evidence (from large particle accelerators) for the physical conditions in the universe back to about ________ after the Big Bang.
A) 1 million years
B) 380,000 years
C) 300 years
D) 3 minutes
E) 10⁻¹⁰ seconds

Accepted Answer

Particle accelerators have allowed scientists to recreate and study conditions similar to those that existed in the universe as early as 10⁻¹⁰ seconds after the Big Bang.

Question 17

What do we mean by inflation?
A) The expansion of universe starting with the instant after the Big Bang
B) A sudden expansion of the universe driven by the energy released when the strong and electroweak forces froze out from the GUT force
C) The rapid expansion of the universe, driven by white dwarf supernova, that we still observe today
D) The sudden release of photons when particles and antiparticles annihilate each other
E) The photons released when electrons and protons first combined, forming the Cosmic Microwave Background Radiation

Accepted Answer

Inflation refers to a sudden and rapid expansion of the universe, which is believed to be driven by the energy released when the strong and electroweak forces froze out from the Grand Unified Theory (GUT) force. This theory is believed to explain a number of observations that cannot be explained by standard cosmology, such as the uniformity of the cosmic microwave background radiation and the large-scale structure of the universe.

Question 18

Why might inflation have occurred at the end of the GUT era?
A) Gravity was an extremely weak force at this period in time.
B) Large amounts of matter and antimatter annihilated at this time.
C) There wasn't enough matter present to slow down the expansion at that time.
D) The universe was too small and needed to grow quickly.
E) An enormous amount of energy was released when the strong and electroweak forces froze out from the GUT force.

Accepted Answer

The enormous amount of energy released when the strong and electroweak forces froze out from the GUT force could have caused inflation at the end of the GUT era. This sudden release of energy could have caused a rapid expansion of the universe, leading to inflation.

Question 19

What happened to all of the quarks that existed freely during the particle era?
A) They combined in groups to make protons, neutrons, and their antiparticles.
B) They froze out of the soup of particles at the end of the era.
C) They evaporated.
D) They combined in groups to make electrons and neutrinos.

Accepted Answer

During the particle era, the universe was filled with a hot, dense soup of particles, including quarks. As the universe expanded and cooled, the quarks combined in groups of two or three to form protons, neutrons, and their antiparticles. This process is known as nucleosynthesis.

Question 20

The Planck era refers to the time period
A) before the Big Bang.
B) before the Planck time.
C) after the Planck time.
D) after inflation.
E) after the GUT era.

Accepted Answer

The Planck era refers to the time period before the Planck time, which is the earliest measurable moment after the Big Bang. It is the point in time where we reach the limits of our current understanding of physics and the laws of nature break down. Therefore, option B is the correct answer.

Quiz 17: The Beginning of Time

How long after the Big Bang was the Planck time, the time at which our current theories become completely unable to describe conditions any earlier in the universe?

Why did the era of nuclei end when the universe was about 380,000 years old?

From what cosmic epoch do the photons in the cosmic background radiation originate?

(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,

Why does the Big Bang theory predict that the cosmic background radiation should have a perfect thermal radiation spectrum?

What kinds of atomic nuclei formed during the nucleosynthesis era?

Which forces have physicists shown to be the same force under conditions of very high temperature, as confirmed by experiments in particle accelerators?

What direct evidence do we have that the weak and electromagnetic forces were once unified as a single force?

A GUT (grand unified theory) refers to theories that

Why can't current theories describe what happened during the Planck era?

How many forces operated in the universe during the GUT era?

Which of the following statements about the cosmic background radiation is not true?

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

Approximately how long did the nucleosynthesis era last?

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?

We have direct experimental evidence (from large particle accelerators) for the physical conditions in the universe back to about ________ after the Big Bang.

What do we mean by inflation?

Why might inflation have occurred at the end of the GUT era?

What happened to all of the quarks that existed freely during the particle era?

The Planck era refers to the time period