Cosmology

1
(No Transcript)
2
The Beginning of Time
3
Somewhere, something incredible is waiting to be
known. - Carl Sagan
4
WHEN I heard the learnd 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
wanderd off by myself, In the mystical moist
night-air, and from time to time, Lookd up in
perfect silence at the stars.
5
WHAT DO YOU THINK?

1. Did the universe have a beginning?
2. Into what is the universe expanding?
3. Will the universe last forever?
4. Are there other universes?
5. Can we ever find out what started everything?
6. 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 universethe 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 dont 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 (Olbers Paradox)

12
Olbers 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
Olbers 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
Olbers Paradox

• Ifthen 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

• Hubbles 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 dont see
  them beyond 13 Billion light years.
• Cosmic Microwave Background Radiation
• The Night Sky is Dark (Olbers Paradox)
• Hubbles 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 Wilsons Horn Antenna used to discover
CMBR
19
(No Transcript)
20
WMAP satellite (2001)
21
(No Transcript)
22
Boomerang Balloon-Lofted Probe above Antarctica
(1998 2003)
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
(No Transcript)
27
Facts Must be explained by a scientific theory
to be considered

• The Night Sky is Dark (Olbers Paradox)
• Hubbles 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 dont 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
(No Transcript)
32
A Big Bang Timeline
33
(No Transcript)
34
(No Transcript)
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 lt 1043 sec)
(small details about) The Big Bang
44
(No Transcript)
45
Planck Era (t lt 1043 sec)
(small details about) The Big Bang

• We are as yet unable to linkquantum mechanics
  general relativity
• We are still trying to describe what happened in
  this era with the LHC!

46
GUT Era (1043 lt t lt 1038 sec)
(small details about) The Big Bang

• The Universe contained two natural forces
• Gravity
• Grand Unified Theory (GUT) force
• electromagnetic strong weak forces unified

47
GUT Era (1043 lt t lt 1038 sec)
(small details about) The Big Bang

• Lasted until Universe was 1038 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
(No Transcript)
49
Electroweak Era
(small details about) The Big Bang
50
Electroweak Era (1038 lt t lt 1010 sec)
(small details about) The Big Bang

• Universe contained three natural forces gravity,
  strong, electroweak
• Lasted until Universe was 1010 sec old.
• Now cooled to 1015 K
• electromagnetic weak forces separated

51
Electroweak Era (1038 lt t lt 1010 sec)
(small details about) The Big Bang

• Experimentally verified in 1983!
• Discovery of W Z bosons
• Electroweak particles predicted to exist above
  1015 K

52
(No Transcript)
53
(No Transcript)
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
(No Transcript)
56
(No Transcript)
57
(No Transcript)
58
(No Transcript)
59
(No Transcript)
60
And now something else is happening

• What is dark matter??
• Why doesnt the universe slow down as much as it
  should be?
• What is dark energy?

61
(No Transcript)
62
What is Dark Matter?

• Recall rotation curve of Milky Way Galaxy.
• Hydrogen beyond our Sun orbit faster than
  predicted by Keplers Law
• Most of Galaxys 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 mattercalled
  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 1930s
• Zwicky found clusters had to be MUCH more
  massive!.
• his proposals of dark matter were met with
  skepticism

67
(No Transcript)
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?
71
Dark Energy ?!?

• If the universe is really larger than it should
  be
• Something must be making it expand
• Energy must be present
• But we cant see its source
• Dark Energy!
• https//www.youtube.com/watch?v3FZv4U5YbNc

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
(No Transcript)
77
Evidence for an Accelerating Universe?
78
(No Transcript)
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)

80
(No Transcript)
81
The critical density!

• How can we tell what the future holds?
• The amount of mass in the volume of space
  controls gravitational forces 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 lt critical density, the Universe will
  expand forever
• if mass gt 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 1029 g / cm3

84
The Critical Density

• BUT all the luminous matter that we observe
  accounts for lt 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 isotropy problem matter-dominated
universe open universe pair production Planck
time primordial fireball primordial
nucleosynthesis quark quintessence radiation-domin
ated 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