Universe Eighth Edition

1. Roger A. Freedman • William J. Kaufmann III Universe Eighth Edition CHAPTER 26 Cosmology

3. Chapter 24 and 26 online quizzes due Thursday 12/9 Skip Chapter 27 Final Exam – Monday 12/13, 5:30-7:30 PM The final will cover chapters 23, 24 and 26 only, same format as Exams 1-3 Last HW!

9. What does it mean to say the universe is expanding? • Galaxies are moving through space away from each other. • Space is expanding, carrying galaxies along with it. • All galaxies are moving away from a point at the center of the universe. • Space is expanding but the galaxies are not carried along with it, so the separation of galaxies does not change. • The galaxies are all getting larger. Q26.2

10. What does it mean to say the universe is expanding? • Galaxies are moving through space away from each other. • Space is expanding, carrying galaxies along with it. • All galaxies are moving away from a point at the center of the universe. • Space is expanding but the galaxies are not carried along with it, so the separation of galaxies does not change. • The galaxies are all getting larger. A26.2

17. Galaxies further away from us have larger cosmological redshifts than those closer to us. What is the cosmological redshift? • A Doppler shift in which the wavelength of photons is increased due to the motion of the galaxies away from us • A Doppler shift in which the wavelength of photons is decreased due to the motion of the galaxies away from us • Photons traveling through space have their wavelength increased because the space through which they are traveling is expanding • Photons traveling through space have their wavelength decreased because the space through which they are traveling is expanding Q26.3

18. Galaxies further away from us have larger cosmological redshifts than those closer to us. What is the cosmological redshift? • A Doppler shift in which the wavelength of photons is increased due to the motion of the galaxies away from us • A Doppler shift in which the wavelength of photons is decreased due to the motion of the galaxies away from us • Photons traveling through space have their wavelength increased because the space through which they are traveling is expanding • Photons traveling through space have their wavelength decreased because the space through which they are traveling is expanding A26.3

41. Which of the following statements about the Big Bang model of cosmology are correct? • The universe began as an infinitely dense cosmic singularity. • The Big Bang can be described as the beginning of time. • The size of the observable universe is related to the age of the universe. • During the first 10-43 second after the Big Bang, the universe was too dense to be described by the known laws of physics. • All of these statements are correct. Q26.6

42. Which of the following statements about the Big Bang model of cosmology are correct? • The universe began as an infinitely dense cosmic singularity. • The Big Bang can be described as the beginning of time. • The size of the observable universe is related to the age of the universe. • During the first 10-43 second after the Big Bang, the universe was too dense to be described by the known laws of physics. • All of these statements are correct. A26.6

43. Key Ideas • The Expansion of the Universe: The Hubble law describes the continuing expansion of space. The redshifts that we see from distant galaxies are caused by this expansion, not by the motions of galaxies through space. • The redshift of a distant galaxy is a measure of the scale of the universe at the time the galaxy emitted its light. • It is meaningless to speak of an edge or center to the universe or of what lies beyond the universe. • The Cosmological Principle: Cosmological theories are based on the idea that on large scales, the universe looks the same at all locations and in every direction.

44. Key Ideas • The Big Bang: The universe began as an infinitely dense cosmic singularity that began its expansion in the event called the Big Bang, which can be described as the beginning of time. • The observable universe extends about 14 billion light-years in every direction from the Earth. We cannot see objects beyond this distance because light from these objects has not had enough time to reach us. • During the first 10-43 second after the Big Bang, the universe was too dense to be described by the known laws of physics.

45. Key Ideas • Cosmic Background Radiation and the Evolution of the Universe: The cosmic microwave background radiation, corresponding to radiation from a blackbody at a temperature of nearly 3 K, is the greatly redshifted remnant of the hot universe as it existed about 380,000 years after the Big Bang. • The background radiation was hotter and more intense in the past. During the first 380,000 years of the universe, radiation and matter formed an opaque plasma called the primordial fireball. When the temperature of the radiation fell below 3000 K, protons and electrons could combine to form hydrogen atoms and the universe became transparent. • The abundance of helium in the universe is explained by the high temperatures in its early history.

46. Key Ideas • The Geometry of the Universe: The curvature of the universe as a whole depends on how the combined average mass density 0 compares to a critical density c. • If 0 is greater than c, the density parameter 0 has a value greater than 1, the universe is closed, and space is spherical (with positive curvature). • If 0 is less than c, the density parameter 0 has a value less than 1, the universe is open, and space is hyperbolic (with negative curvature). • If 0 is equal to c, the density parameter 0 is equal to 1 and space is flat (with zero curvature).

47. Key Ideas • Cosmological Parameters and Dark Energy: Observations of temperature variations in the cosmic microwave background indicate that the universe is flat or nearly so, with a combined average mass density equal to the critical density. Observations of galaxy clusters suggest that the average density of matter in the universe is about 0.24 of the critical density. The remaining contribution to the average density is called dark energy. • Measurements of Type Ia supernovae in distant galaxies show that the expansion of the universe is speeding up. This may be due to the presence of dark energy in the form of a cosmological constant, which provides a pressure that pushes the universe outward.

48. Key Ideas • Cosmological Parameters and Primordial Sound Waves: Temperature variations in the cosmic background radiation are a record of sound waves in the early universe. Studying the character of these sound waves, and the polarization of the background radiation that they produce, helps constrain models of the universe.