1. FIGURE 18-19 Cosmic Timeline
This figure shows our current
thinking about the evolution of star and galaxy formation
in the universe. (Don Dixon)

2. The Beginning of Time

3. Somewhere, something incredible is waiting to be known.
- Carl Sagan

4. WHEN I heard the learn’d astronomer;
When the proofs, the figures, were ranged in columns before me;
When I was shown the charts and the diagrams, to add, divide, and measure them;
When I, sitting, heard the astronomer, where he lectured with much applause in the lecture-room,
How soon, unaccountable, I became tired and sick;
Till rising and gliding out, I wander’d off by myself,
In the mystical moist night-air, and from time to time,
Look’d up in perfect silence at the stars.

5. WHAT DO YOU THINK? Did the universe have a beginning?
Into what is the universe expanding?
Will the universe last forever?
Are there other universes?
Can we ever find out what started everything?
Should we try??

6. In this chapter you will discover…
Cosmology, which seeks to explain how the universe began, how it evolves, and its fate
Um… not COSMETOLOGY…

7. In this chapter you will discover…
Cosmology, which seeks to explain how the universe began, how it evolves, and its fate
The best theory that we have for the evolution of the universe—the Big Bang
How astronomers trace the emergence of matter and the formation of galaxies

8. Key Essay Questions How did the universe begin? How will it end?
How do we know? What evidence do we have?

9. Facts Must be explained by a scientific theory to be considered
Quasars more prevalent far away; we don’t see them beyond ~ 13 Billion light years.

10. Facts Must be explained by a scientific theory to be considered
Cosmic Microwave Background Radiation

11. Facts Must be explained by a scientific theory to be considered
The Night Sky is Dark (Olber’s Paradox)

12. Olber’s Paradox – Why is the Night Sky Dark?
If the universe contains an infinite number of stars, uniformly distributed in space, and the universe is infinitely old, then:

13. Olber’s Paradox – Why is the Night Sky Dark?
If the universe contains an infinite number of stars, uniformly distributed in space, and the universe is infinitely old, then:
Overall brightness received in any direction from those stars is constant.
Farther away, more space, but more stars in that space.
In every direction, eventually look at surface of a star, so….
Every point in the sky should be as bright as the surface of a star.

14. Olber’s Paradox If…then logical argument assumption  conclusion
Clearly the night sky IS dark
The conclusion is false so one or more assumptions must be incorrect!
The universe is not infinite in size, and not infinite in age!

15. Facts Must be explained by a scientific theory to be considered
Hubble’s Law: Distant Galaxies move away from us, faster. The Universe is changing in time.

16. Facts Must be explained by a scientific theory to be considered
90% of the Universe is Hydrogen, 10% is Helium

17. Facts Must be explained by a scientific theory to be considered
Quasars more prevalent far away; we don’t see them beyond ~ 13 Billion light years.
Cosmic Microwave Background Radiation
The Night Sky is Dark (Olber’s Paradox)
Hubble’s Law: Distant Galaxies move away from us, faster. The Universe is changing in time.
90% of the Universe is Hydrogen, 10% is Helium

18. Penzias & Wilson’s Horn Antenna used to discover CMBR
FIGURE 18-2 Bell Labs Horn Antenna
This Bell Laboratories
horn antenna at Holmdel, New Jersey, was used by Arno
Penzias (right) and Robert Wilson in 1965 to detect the
cosmic microwave background. (Lucent Technologies, Bell
Laboratories)

19. FIGURE 18-4 Spectrum of the Cosmic Microwave Background
The little squares on this graph are COBE’s measurements of the
brightness of the cosmic microwave background plotted against
wavelength. To a remarkably high degree of accuracy, the data
fall along a blackbody curve for 2.73 K. The peak of the curve
is at a wavelength of 1.1 mm, in accordance with Wien’s law.
(Courtesy of E. Cheng; NASA COBE Science Team)

20. WMAP satellite (2001) FIGURE 18-3 In Search of Primordial Photons
(a) The Wilkinson Microwave Anisotropy Probe (WMAP) satellite,
launched in 2001, improved upon the measurements of the
spectrum and angular distribution of the cosmic microwave
background taken by the COBE satellite. (b) The balloon carried
telescope BOOMERANG orbited above Antarctica
for 10 days, collecting data used to resolve the cosmic microwave
background, with 10 times higher resolution than that
of COBE. All of these experiments found local temperature
variations across the sky but no overall deviation from a
blackbody spectrum. (a: NASA/WMAP Science Team; b: The
BOOMERANG Group, University of California, Santa Barbara)

21. FIGURE 18-15 Structure of the Early Universe
This microwave map of the entire sky, produced from data taken by the Wilkinson Microwave
Anisotropy Probe (WMAP), shows temperature variations in the cosmic
microwave background. Red regions are about K warmer than
the average temperature of 2.73 K; blue regions are about K
cooler than the average. Inset: These tiny temperature fluctuations,
observed by BOOMERANG, are related to the large-scale structure of the
universe today, indicating where superclusters and voids grew. The radiation
detected to make this map is from a time 379,000 years after the Big
Bang. (NASA/WMAP Science Team; inset: NSF/NASA)

22. Boomerang Balloon-Lofted Probe above Antarctica (1998 & 2003)
FIGURE 18-3 In Search of Primordial Photons
(a) The Wilkinson Microwave Anisotropy Probe (WMAP) satellite,
launched in 2001, improved upon the measurements of the
spectrum and angular distribution of the cosmic microwave
background taken by the COBE satellite. (b) The balloon carried
telescope BOOMERANG orbited above Antarctica
for 10 days, collecting data used to resolve the cosmic microwave
background, with 10 times higher resolution than that
of COBE. All of these experiments found local temperature
variations across the sky but no overall deviation from a
blackbody spectrum. (a: NASA/WMAP Science Team; b: The
BOOMERANG Group, University of California, Santa Barbara)

23. What is the Cosmic Microwave Background?
Relic “heat” energy from Big Bang
Released ~ 1/2 million years after Bang

24. What is the Cosmic Microwave Background?
Before ~ ½ million years, universe was a “sea” of high energy particles & photons
After, universe cools, allowing neutral matter to form

25. What is the Cosmic Microwave Background?
Radiation then is visible through space
Redshifted as universe expands

26. FIGURE 18-1 Cosmological Redshift
Just as the waves
drawn on this rubber band are stretched along with the rubber
band, so too are the wavelengths of photons stretched as
the universe expands.

27. Facts Must be explained by a scientific theory to be considered
The Night Sky is Dark (Olber’s Paradox)
Hubble’s Law: Distant Galaxies move away from us, faster. The Universe is changing in time.
90% of the Universe is Hydrogen, 10% is Helium
Cosmic Microwave Background Radiation
Quasars more prevalent far away; we don’t see them beyond ~ 13 Billion light years.

28. Assumptions
Physics: The laws we know of around us work everywhere in the same way.
Isotropy: The Universe looks the same as it appears to us – everywhere
Homogeneity: The Universe is made of the same stuff we see around us - everywhere

29. Facts + Assumptions Theory
The Big Bang Theory
The universe started ~ 14 Billion years ago
All energy, incredibly hot and dense
Expands incredibly fast (inflation)
Matter (protons, electrons, neutrons) created from energy (E = mc2)

30. Facts + Assumptions Theory
The Big Bang Theory
Some protons (Hydrogen) fuse to create Helium
Universe cools and expands
Eventually, neutral atoms form…
“Recombination” era is when CBR can be seen

31. FIGURE 18-14 Era of Recombination
(a) Before recombination,
the energies of photons in the cosmic background were
high enough to prevent protons and electrons from forming
hydrogen atoms. (b) As soon as the energy of the background
radiation became too low to ionize hydrogen, neutral atoms
came into existence.

32. A Big Bang Timeline… FIGURE 18-19 Cosmic Timeline
This figure shows our current
thinking about the evolution of star and galaxy formation
in the universe. (Don Dixon)
A Big Bang Timeline…

33. FIGURE 18-19 Cosmic Timeline
This figure shows our current
thinking about the evolution of star and galaxy formation
in the universe. (Don Dixon)

34. FIGURE 18-19 Cosmic Timeline
This figure shows our current
thinking about the evolution of star and galaxy formation
in the universe. (Don Dixon)

35. A Scientific Story…
What would the universe have been like in the first few …
billionths of billionths of a second?
Seconds?
Three Minutes?
Why did the universe expand so quickly?
When did galaxies form?
Why did galaxies form?

36. Conditions in the Early Universe
Most distant quasars & galaxies observed from time when Universe was ~ 1 billion years old.
Cosmic microwave background is earliest light available (~400,000 years after Big Bang)
How to know conditions at beginning of time?

37. Conditions in the Early Universe
Know forces, conditions & expansion rate of Universe today.
Run expansion backwards, model early universe!

38. Running the film backwards….
Today: FOUR forces seen in nature
Gravity (longest distance, weakest force)

39. Running the film backwards….
Today: FOUR forces seen in nature
Gravity (longest distance, weakest force)
Electromagnetic (light!)

40. Running the film backwards….
Today: FOUR forces seen in nature
Gravity (longest distance, weakest force)
Electromagnetic (light!)
Weak (radioactive decay, neutron decay)

41. Running the film backwards….
Today: FOUR forces seen in nature
Gravity (longest distance, weakest force)
Electromagnetic (light!)
Weak (radioactive decay, neutron decay)
Strong (“nuclear glue force”)

42. Running the film backwards….
Today: Successfully created tests conditions in lab to link Electromagnetic, Weak, Strong forces
“The Grand Unified Theory”
We hypothesize that all four natural forces were unified during VERY early universe

43. Planck Era (t < 10–43 sec)
(small details about) The Big Bang
Planck Era (t < 10–43 sec)

44. FIGURE 18-7 Unification of the Four Forces
The strength of the four physical forces depends on the speed with which
particles interact or, equivalently, their temperature. As
shown in this figure, the higher the temperature of the universe,
the more the forces resemble each other. Also included
here are the ages of the universe at which the various
forces were equal.

45. “Planck Era” (t < 10–43 sec)
(small details about) The Big Bang
“Planck Era” (t < 10–43 sec)
We are as yet unable to link… quantum mechanics & general relativity
We are still trying to describe what happened in this era with the LHC!

46. GUT Era (10–43 < t < 10–38 sec)
(small details about) The Big Bang
GUT Era (10–43 < t < 10–38 sec)
The Universe contained two natural forces:
Gravity
Grand Unified Theory (GUT) force
electromagnetic + strong + weak forces unified

47. GUT Era (10–43 < t < 10–38 sec)
(small details about) The Big Bang
GUT Era (10–43 < t < 10–38 sec)
Lasted until Universe was 10–38 sec old.
“cooled” to 1029 K
strong force emerges separate and distinct from electro-weak force
energy released by this caused a sudden and dramatic inflation of the size of the Universe

48. FIGURE 18-10 Observable Universe Before and After Inflation
Shortly after the Big Bang, the universe expanded by
a factor of about 1050 due to inflation. This growth in the size
of the presently observable universe occurred in a very brief
time (shaded interval).

49. (small details about) The Big Bang
Electroweak Era

50. Electroweak Era (10–38 < t < 10–10 sec)
(small details about) The Big Bang
Electroweak Era (10–38 < t < 10–10 sec)
Universe contained three natural forces: gravity, strong, & electroweak
Lasted until Universe was 10–10 sec old.
Now “cooled” to 1015 K
electromagnetic & weak forces separated

51. Electroweak Era (10–38 < t < 10–10 sec)
(small details about) The Big Bang
Electroweak Era (10–38 < t < 10–10 sec)
Experimentally verified in 1983!
Discovery of W & Z bosons
Electroweak particles predicted to exist above 1015 K

52. FIGURE 18-8 Early History of the Universe
Current theory holds that, as the universe cooled, the four forces separated
from their initial unified state. The inflationary epoch lasted
from 1035 s to 1024 s after the Big Bang. Quarks became
confined together, thereby creating neutrons and protons
106 s after the Big Bang. The universe became transparent
to light (i.e., photons decoupled from matter) when the universe
was about s (379,000 years) old. The
physics of the Planck era is presently unknown.

54. And then something happens…
From this high-energy state, galaxies and stars must eventually form
What triggers galaxy formation?
Why bubbles and voids?

55. FIGURE 18-16 Galaxies Forming by Combining Smaller Units
(a) This painting indicates how astronomers visualize the
burst of star formation that occurred within a few hundred million
years after the Big Bang. The arcs and irregular circles
represent interstellar gas illuminated by supernovae. (b) Using
the Hubble and Keck telescopes, astronomers discovered two
groups of stars (arrows) 13.4 billion light years away that are
believed to be protogalaxies, from which bigger galaxies
grew. These protogalaxies were discovered because they were
enlarged by the gravitational lensing of an intervening cluster
of galaxies. (c) The Chandra X-ray telescope imaged gravitationally
bound gas around the distant galaxy 3C 294. The
X-ray emission from this gas is the signature of an extremely
massive cluster of galaxies, in this case, at a distance of about
11.2 billion light years from us. (a: Adolf Schaller, STScI/NASA/K.
Lanzetta, SUNY; b: Richard Ellis (Caltech) and Jean-Paul Kneib
(Observatorie Midi-Pyrenees, France), NASA, ESA; c: NASA)

56. FIGURE 18-16 Galaxies Forming by Combining Smaller Units
(a) This painting indicates how astronomers visualize the
burst of star formation that occurred within a few hundred million
years after the Big Bang. The arcs and irregular circles
represent interstellar gas illuminated by supernovae. (b) Using
the Hubble and Keck telescopes, astronomers discovered two
groups of stars (arrows) 13.4 billion light years away that are
believed to be protogalaxies, from which bigger galaxies
grew. These protogalaxies were discovered because they were
enlarged by the gravitational lensing of an intervening cluster
of galaxies. (c) The Chandra X-ray telescope imaged gravitationally
bound gas around the distant galaxy 3C 294. The
X-ray emission from this gas is the signature of an extremely
massive cluster of galaxies, in this case, at a distance of about
11.2 billion light years from us. (a: Adolf Schaller, STScI/NASA/K.
Lanzetta, SUNY; b: Richard Ellis (Caltech) and Jean-Paul Kneib
(Observatorie Midi-Pyrenees, France), NASA, ESA; c: NASA)

57. FIGURE 18-16 Galaxies Forming by Combining Smaller Units
(a) This painting indicates how astronomers visualize the
burst of star formation that occurred within a few hundred million
years after the Big Bang. The arcs and irregular circles
represent interstellar gas illuminated by supernovae. (b) Using
the Hubble and Keck telescopes, astronomers discovered two
groups of stars (arrows) 13.4 billion light years away that are
believed to be protogalaxies, from which bigger galaxies
grew. These protogalaxies were discovered because they were
enlarged by the gravitational lensing of an intervening cluster
of galaxies. (c) The Chandra X-ray telescope imaged gravitationally
bound gas around the distant galaxy 3C 294. The
X-ray emission from this gas is the signature of an extremely
massive cluster of galaxies, in this case, at a distance of about
11.2 billion light years from us. (a: Adolf Schaller, STScI/NASA/K.
Lanzetta, SUNY; b: Richard Ellis (Caltech) and Jean-Paul Kneib
(Observatorie Midi-Pyrenees, France), NASA, ESA; c: NASA)

58. FIGURE 18-16 Galaxies Forming by Combining Smaller Units
(a) This painting indicates how astronomers visualize the
burst of star formation that occurred within a few hundred million
years after the Big Bang. The arcs and irregular circles
represent interstellar gas illuminated by supernovae. (b) Using
the Hubble and Keck telescopes, astronomers discovered two
groups of stars (arrows) 13.4 billion light years away that are
believed to be protogalaxies, from which bigger galaxies
grew. These protogalaxies were discovered because they were
enlarged by the gravitational lensing of an intervening cluster
of galaxies. (c) The Chandra X-ray telescope imaged gravitationally
bound gas around the distant galaxy 3C 294. The
X-ray emission from this gas is the signature of an extremely
massive cluster of galaxies, in this case, at a distance of about
11.2 billion light years from us. (a: Adolf Schaller, STScI/NASA/K.
Lanzetta, SUNY; b: Richard Ellis (Caltech) and Jean-Paul Kneib
(Observatorie Midi-Pyrenees, France), NASA, ESA; c: NASA)

59. FIGURE 18-16 Galaxies Forming by Combining Smaller Units
(a) This painting indicates how astronomers visualize the
burst of star formation that occurred within a few hundred million
years after the Big Bang. The arcs and irregular circles
represent interstellar gas illuminated by supernovae. (b) Using
the Hubble and Keck telescopes, astronomers discovered two
groups of stars (arrows) 13.4 billion light years away that are
believed to be protogalaxies, from which bigger galaxies
grew. These protogalaxies were discovered because they were
enlarged by the gravitational lensing of an intervening cluster
of galaxies. (c) The Chandra X-ray telescope imaged gravitationally
bound gas around the distant galaxy 3C 294. The
X-ray emission from this gas is the signature of an extremely
massive cluster of galaxies, in this case, at a distance of about
11.2 billion light years from us. (a: Adolf Schaller, STScI/NASA/K.
Lanzetta, SUNY; b: Richard Ellis (Caltech) and Jean-Paul Kneib
(Observatorie Midi-Pyrenees, France), NASA, ESA; c: NASA)

60. And now something else is happening…
What is dark matter??
Why doesn’t the universe slow down as much as it should be?
What is dark energy?

62. What is Dark Matter? Recall rotation curve of Milky Way Galaxy.
Hydrogen beyond our Sun orbit faster than predicted by Kepler’s Law
Most of Galaxy’s light from stars closer to center

63. What is Dark Matter? Two possible explanations:
We do not understand gravity (on galaxy-size+ scales)
Higher velocities of Hydrogen gas caused by gravitational attraction of unseen matter…called dark matter

64. What is Dark Matter? IF we trust our theory of gravity...
there may be 10 times more dark than luminous matter in our Galaxy
luminous matter is confined to the disk
dark matter is found in the halo and far beyond the luminous disk

65. And still more Dark Matter!
In other galaxies, we “see” same phenomena
Rotation Curves of Spirals
In clusters of galaxies, too
Measuring Motions of galaxies
Measuring “Temperature” of gas
Gravitational Lensing

66. Velocities in Clusters of Galaxies
Pioneered by Fritz Zwicky in 1930’s
Zwicky found clusters had to be MUCH more massive!.
his proposals of dark matter were met with skepticism

67. FIGURE 18-20 Mapping Dark Matter
(Top) The Hubble Space Telescope observed that galaxies in the same direction,
but at different distances from Earth, undergo different amounts
of gravitational lensing. Much of this effect is due to dark matter.
By subtracting out the lensing effects of intervening galaxies, the
distorted shapes of the galaxies at various distances enable
astronomers to determine the (Bottom) distribution of dark matter.
(NASA, ESA, and R. Massey [CIT])

68. Gravitational Lensing
Theory of Relativity states that massive objects distort spacetime.
Massive cluster bends path of light (like a lens)
Blue arcs are lensed images of galaxy behind cluster

69. Agreement between methods
Cluster masses measured by all three independent methods agree:
Most galaxy clusters contain greater than 100 times more mass than accounted for by light of stars within them!
Galaxy clusters contain far more mass in dark matter than in stars

70. A problem on the horizon?
FIGURE Dimmer Distant Supernova
(a) These Hubble Space
Telescope images show the galaxy in which the supernova SN 1997ff occurred.
This supernova, more than 10 billion light years away, was dimmer than expected,
indicating that the distance to it is greater than the distance it would have,
if the universe had been continually slowing down since the Big Bang. This supports
the notion that an outward (cosmological) force is acting over vast distances
in the universe. The arrow on the first inset shows the galaxy in which the
supernova was discovered. The bright spot on the second inset shows the supernova
by subtracting the constant light emitted by all the other nearby objects.
(b) The distances and brightnesses of many very distant supernovae are plotted
on this diagram. The locations of the most distant supernovae in the upper
region strongly indicate that the universe has been accelerating outward for the
past 6 billion years. (a: Adam Riess, Space Telescope Science Institute, NASA)

71. Dark Energy ?!?#% Dark Energy!
If the universe is really larger than it should be…
Something must be making it expand…
Energy must be present
But we can’t see its source:
Dark Energy!

72. Why is Dark Energy Important?
Consider ultimate fate of the universe…
Option 1: Universe continues to expand, slows, stops, recollapses….
(The big “crunch”)

73. Why is Dark Energy Important?
Consider ultimate fate of the universe…
Option 2: Universe continues to expand, accelerating faster and faster
(The big “stretch”)

74. The Geometry of Space Space (and Time!) can take the shape of
Volume reaches a maximum size, then recollapses, or
Infinitely expanding volume, accelerating over time, or…
Volume that gets bigger, but slows down to eventual stop (in an infinite amount of time)

75. The Geometry of Space Space (and Time!) can take the shape of
Volume reaches a maximum size, then recollapses (CLOSED)
An infinitely expanding volume, accelerating over time (OPEN)
A volume that gets bigger, but slows down to eventual stop in an infinite amount of time (FLAT)

76. FIGURE 18-22 Cosmic Microwave Background and the Curvature of Space
Temperature variations in the early universe
appear as “hot spots” in the cosmic microwave background.
The apparent sizes of these spots depend on the curvature
of space. (a) In a closed universe with positive curvature,
light rays from opposite sides of a hot spot bend toward each
other. Hence, the hot spot appears larger than it actually is
(dashed lines). (b) The light rays do not bend in a flat universe.
(c) In an open universe, light rays bend apart. The dashed lines
show that a hot spot would appear smaller than its actual size.
(The BOOMERANG Group, University of California, Santa Barbara)

77. Evidence for an Accelerating Universe?

78. FIGURE 18-23 Dimmer Distant Supernova
(a) These Hubble Space
Telescope images show the galaxy in which the supernova SN 1997ff occurred.
This supernova, more than 10 billion light years away, was dimmer than expected,
indicating that the distance to it is greater than the distance it would have,
if the universe had been continually slowing down since the Big Bang. This supports
the notion that an outward (cosmological) force is acting over vast distances
in the universe. The arrow on the first inset shows the galaxy in which the
supernova was discovered. The bright spot on the second inset shows the supernova
by subtracting the constant light emitted by all the other nearby objects.
(b) The distances and brightnesses of many very distant supernovae are plotted
on this diagram. The locations of the most distant supernovae in the upper
region strongly indicate that the universe has been accelerating outward for the
past 6 billion years. (a: Adam Riess, Space Telescope Science Institute, NASA)

79. Four Models for the Future of the Universe
Recollapsing Universe: the expansion will someday halt and reverse
Critical Universe: will not collapse, but will expand more slowly with time
Coasting Universe: will expand forever with little slowdown
Accelerating Universe: the expansion will accelerate with time (currently “favored”)

81. The critical density! How can we tell what the future holds?
The amount of mass in the volume of space controls gravitational force’s impact
Estimating “critical density” is key!

82. The Critical Density
IF gravitational attraction between galaxies can overcome the expansion of the Universe in localized regions.
how strong must gravity be to stop the entire Universe from expanding?
it depends on the total mass density of the Universe

83. The Critical Density
if mass < critical density, the Universe will expand forever
if mass > critical density, the Universe will stop expanding and then contract
The value of Ho tells us the current kinetic energy of the Universe AND indicates the critical density is 10–29 g / cm3

84. The Critical Density
BUT all the luminous matter that we observe accounts for < 1% of critical density
And for dark matter to stop Universal expansion, even more would be required…
This line of research suggests the Universe will expand forever!

85. Key Terms isotropy Big Bang isotropy problem closed universe
matter-dominated universe
open universe
pair production
Planck time
primordial fireball
primordial nucleosynthesis
quark
quintessence
radiation-dominated universe
strong nuclear force
superstring theories
Theories of Everything
universe
weak nuclear force
Big Bang
closed universe
confinement
cosmic light horizon
cosmic microwave background
cosmological constant
cosmological redshift
cosmology
dark ages
dark energy
decoupling
era of recombination
expanding universe
Grand Unified Theory (GUT)
homogeneity
horizon problem
inflation
inflationary epoch