UniverseUniverseEighth EditionEighth Edition

UniverseUniverseEighth EditionEighth Edition

Roger A. Freedman • William J. Kaufmann III

CHAPTER 26CHAPTER 26CosmologyCosmology

CHAPTER 26CHAPTER 26CosmologyCosmology

Chapter 24 and 26 online quizzes due Thursday Chapter 24 and 26 online quizzes due Thursday 12/912/9

Skip Chapter 27Skip Chapter 27

Final Exam – Monday 12/13, 5:30-7:30 PMFinal Exam – Monday 12/13, 5:30-7:30 PM

The final will cover chapters 23, 24 and 26 only, The final will cover chapters 23, 24 and 26 only, same format as Exams 1-3 same format as Exams 1-3

Last HW!

What does it mean to say the universe is expanding?

A. Galaxies are moving through space away from each other.

B. Space is expanding, carrying galaxies along with it.

C. All galaxies are moving away from a point at the center of the universe.

D. Space is expanding but the galaxies are not carried along with it, so the separation of galaxies does not change.

E. The galaxies are all getting larger.

Q26.2

What does it mean to say the universe is expanding?

A. Galaxies are moving through space away from each other.

B. Space is expanding, carrying galaxies along with it.

C. All galaxies are moving away from a point at the center of the universe.

D. Space is expanding but the galaxies are not carried along with it, so the separation of galaxies does not change.

E. The galaxies are all getting larger.

A26.2

Galaxies further away from us have larger cosmological redshifts than those closer to us. What is the cosmological redshift?

A. A Doppler shift in which the wavelength of photons is increased due to the motion of the galaxies away from us

B. A Doppler shift in which the wavelength of photons is decreased due to the motion of the galaxies away from us

C. Photons traveling through space have their wavelength increased because the space through which they are traveling is expanding

D. Photons traveling through space have their wavelength decreased because the space through which they are traveling is expanding

Q26.3

Galaxies further away from us have larger cosmological redshifts than those closer to us. What is the cosmological redshift?

A. A Doppler shift in which the wavelength of photons is increased due to the motion of the galaxies away from us

B. A Doppler shift in which the wavelength of photons is decreased due to the motion of the galaxies away from us

C. Photons traveling through space have their wavelength increased because the space through which they are traveling is expanding

D. Photons traveling through space have their wavelength decreased because the space through which they are traveling is expanding

A26.3

Which of the following statements about the Big Bang model of cosmology are correct?

A. The universe began as an infinitely dense cosmic singularity.

B. The Big Bang can be described as the beginning of time.

C. The size of the observable universe is related to the age of the universe.

D. During the first 10-43 second after the Big Bang, the universe was too dense to be described by the known laws of physics.

E. All of these statements are correct.

Q26.6

Which of the following statements about the Big Bang model of cosmology are correct?

A. The universe began as an infinitely dense cosmic singularity.

B. The Big Bang can be described as the beginning of time.

C. The size of the observable universe is related to the age of the universe.

D. During the first 10-43 second after the Big Bang, the universe was too dense to be described by the known laws of physics.

E. All of these statements are correct.

A26.6

Key Ideas The Expansion of the Universe:The Expansion of the Universe: The Hubble law The Hubble law

describes the continuing expansion of space. The describes the continuing expansion of space. The redshifts that we see from distant galaxies are caused by redshifts that we see from distant galaxies are caused by this expansion, not by the motions of galaxies through this expansion, not by the motions of galaxies through space.space.

The redshift of a distant galaxy is a measure of the scale The redshift of a distant galaxy is a measure of the scale of the universe at the time the galaxy emitted its light.of the universe at the time the galaxy emitted its light.

It is meaningless to speak of an edge or center to the It is meaningless to speak of an edge or center to the universe or of what lies beyond the universe.universe or of what lies beyond the universe.

The Cosmological Principle:The Cosmological Principle: Cosmological theories Cosmological theories are based on the idea that on large scales, the universe are based on the idea that on large scales, the universe looks the same at all locations and in every direction.looks the same at all locations and in every direction.

Key Ideas The Big Bang:The Big Bang: The universe began as an infinitely The universe began as an infinitely

dense cosmic singularity that began its expansion in the dense cosmic singularity that began its expansion in the event called the Big Bang, which can be described as event called the Big Bang, which can be described as the beginning of time.the beginning of time.

The observable universe extends about 14 billion light-The observable universe extends about 14 billion light-years in every direction from the Earth. We cannot see years in every direction from the Earth. We cannot see objects beyond this distance because light from these objects beyond this distance because light from these objects has not had enough time to reach us.objects has not had enough time to reach us.

During the first 10During the first 10-43 -43 second after the Big Bang, the second after the Big Bang, the universe was too dense to be described by the known universe was too dense to be described by the known laws of physics.laws of physics.

Key Ideas Cosmic Background Radiation and the Evolution of the Cosmic Background Radiation and the Evolution of the

Universe: Universe: The cosmic microwave background radiation, The cosmic microwave background radiation, corresponding to radiation from a blackbody at a temperature corresponding to radiation from a blackbody at a temperature of nearly 3 K, is the greatly redshifted remnant of the hot of nearly 3 K, is the greatly redshifted remnant of the hot universe as it existed about 380,000 years after the Big Bang.universe as it existed about 380,000 years after the Big Bang.

The background radiation was hotter and more intense in the The background radiation was hotter and more intense in the past. During the first 380,000 years of the universe, radiation past. During the first 380,000 years of the universe, radiation and matter formed an opaque plasma called the primordial and matter formed an opaque plasma called the primordial fireball. When the temperature of the radiation fell below 3000 fireball. When the temperature of the radiation fell below 3000 K, protons and electrons could combine to form hydrogen K, protons and electrons could combine to form hydrogen atoms and the universe became transparent.atoms and the universe became transparent.

The abundance of helium in the universe is explained by the The abundance of helium in the universe is explained by the high temperatures in its early history.high temperatures in its early history.

Key Ideas The Geometry of the Universe:The Geometry of the Universe: The curvature of the The curvature of the

universe as a whole depends on how the combined universe as a whole depends on how the combined average mass density average mass density 0 0 compares to a critical density compares to a critical density cc..

If If 00 is greater than is greater than cc, the density parameter , the density parameter 00 has a has a value greater than 1, the universe is closed, and space is value greater than 1, the universe is closed, and space is spherical (with positive curvature).spherical (with positive curvature).

If If 00 is less than is less than cc, the density parameter , the density parameter 00 has a value has a value less than 1, the universe is open, and space is less than 1, the universe is open, and space is hyperbolic (with negative curvature).hyperbolic (with negative curvature).

If If 00 is equal to is equal to cc, the density parameter , the density parameter 00 is equal to 1 is equal to 1 and space is flat (with zero curvature).and space is flat (with zero curvature).

Key Ideas Cosmological Parameters and Dark Energy:Cosmological Parameters and Dark Energy:

Observations of temperature variations in the cosmic Observations of temperature variations in the cosmic microwave background indicate that the universe is flat or microwave background indicate that the universe is flat or nearly so, with a combined average mass density equal to nearly so, with a combined average mass density equal to the critical density. Observations of galaxy clusters the critical density. Observations of galaxy clusters suggest that the average density of matter in the universe suggest that the average density of matter in the universe is about 0.24 of the critical density. The remaining is about 0.24 of the critical density. The remaining contribution to the average density is called dark energy.contribution to the average density is called dark energy.

Measurements of Type Ia supernovae in distant galaxies Measurements of Type Ia supernovae in distant galaxies show that the expansion of the universe is speeding up. show that the expansion of the universe is speeding up. This may be due to the presence of dark energy in the This may be due to the presence of dark energy in the form of a cosmological constant, which provides a form of a cosmological constant, which provides a pressure that pushes the universe outward.pressure that pushes the universe outward.

Key Ideas Cosmological Parameters and Primordial Sound Cosmological Parameters and Primordial Sound

Waves:Waves: Temperature variations in the cosmic Temperature variations in the cosmic background radiation are a record of sound waves in the background radiation are a record of sound waves in the early universe. Studying the character of these sound early universe. Studying the character of these sound waves, and the polarization of the background radiation waves, and the polarization of the background radiation that they produce, helps constrain models of the that they produce, helps constrain models of the universe.universe.