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Title: Recent Developments in Cosmology


1
Recent Developments in Cosmology
Josh Frieman
Quarknet, Argonne National Laboratory, July 2002

2
Cosmology an ancient endeavor
  • How did the world around us come into being?
  • Has it always been like this or has it evolved?
  • If the Universe is changing, how did it begin and
    what will
  • it be like in the future? And (how) will it
    end?
  • Early Cosmology the Universe evolved from a
    beginning
  • ?Babylonian cosmology Enuma elish
  • ?Judeo-Christian cosmology Genesis
  • ?Greek and Roman myths and
    philosophers
  • Modern cosmology expanding Universe established
    1929,
  • evolving Universe established in 1965
    (discovery of Cosmic
  • Microwave Background Radiation by Penzias
    Wilson,
  • Nobel Prize in 1978)


3
Modern Science --The Universe is knowable
through repeatable observations --The
Universe can be described in terms of universal
physical laws Modern CosmologyArchaeology on
the Grand Scale --We cannot (yet) create
universes in the laboratory and study them
--We must observe stars, galaxies, cosmic
radiations, etc, and use them as pottery
shards to reconstruct what the Universe was
like at much earlier times, to weave a coherent
story of cosmic evolution based on our
understanding of physical laws. Fortunately,
there are surprisingly few ways (given the laws
of physics) to make a Universe that
looks like ours today.
4
The macroscopic Universe observed a
hierarchy of Structure...
5
Human scale Size 100 cm Mass 100 kg 1029
atoms Density 0.6 gm/cm3 Structures organized
by atomic interactions Sarah Frieman b. March
26, 2001
6
Planets Size 1010 cm1010 cm
Mass 1026 kg 1054 atoms
Density 0.6 gm/cm3 Structures determined by
atomic interactions gravity
7
Brown Dwarf Star (Planet/star transition)
Ordinary Stars Size 1011 cm Mass 1030 kg
1057 atoms Density
0.5 gm/cm3 Hot gas bound by gravity
8
M87 Nebula in Orion (star forming region in our
galaxy)
Interstellar gas clouds star clusters Size
1 parsec 3 light-yr 3 x 1018 cm Mass
105 Msun
9
An Infrared view of the Milky Way (our galaxy)
Galaxies Size 1022 cm 10 kiloparsec (kpc)
Mass 1011 Msun Self-gravitating
systems of stars, gas, and dark matter
10
A Brief Tour of Galaxies
Images from the Sloan Digital Sky Survey
(SDSS) An on-going project to map the
Universe, the SDSS will catalog roughly 70
million galaxy images and measure 3D
positions for 700,000 of them by the time
it is completed in 2005
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12
UGC 03214 edge-on spiral galaxy in Orion
13
NGC 1087 spiral galaxy in Aries
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17
Clusters of Galaxies Size 1025 cm Megaparsec
(Mpc) Mass 1015 Msun Largest
gravitationally bound objects galaxies, gas,
dark matter
18
Cluster of Galaxies
giant arcs are galaxies behind the cluster,
gravitationally lensed by it
19
Gravitational Lensing
Basically, the same effects that occur in more
familiar optical circumstances magnification
and distortion
Objects farther from the line of sight are
distorted less.
20
Helen Frieman b. 9/20/99
21
Helen behind a Black Hole Gravitational Lens
22
Mapping the Mass in a Cluster of Galaxies via
Gravitational Lensing Most of the Mass in the
Universe is Dark (it doesnt shine) Dark
Matter
23
Superclusters and Large-scale Structure
Filaments, Walls, and Voids of Galaxies
100 Million parsecs (Mpc)
You Are Here
Pizza Slice 6 degrees thick containing 1060
galaxies position of each galaxy
represented by a single dot
24
Superclusters and Large-scale Structure
Filaments, Walls, and Voids of Galaxies
100 Million parsecs (Mpc)
You Are Here
25
Superclusters and Large-scale Structure
Filaments, Walls, and Voids of Galaxies
Coma cluster of galaxies
100 Million parsecs (Mpc)
You Are Here
26
Early SDSS Data 200,000 Galaxies Mapped in
3D so far
27
Evolution of the Universe
What we know (what is well-established by
observations) The Standard
Cosmology Speculations/theories that extend
beyond the well-established and attempt to
explain otherwise unexplained phenomena.
28
The Big Bang Theorya well-tested framework for
understanding the observationsand for asking new
questions
The Universe has been expanding isotropically
from a hot, dense beginning (aka the Big Bang)
for about 14 billion years The only successful
framework we have for explaining several key
facts about the Universe ?Hubbles law of
galaxy recessionexpansion ?Uniformity
(isotropy) of Microwave background ?Cosmic
abundances of the light elements
Hydrogen, Helium, Deuterium, Lithium, cooked in
the first 3 minutes

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31
The Big Bang Theory
Not just a theory, but one of the most firmly
established paradigms in science
The Standard Cosmological Model
32
The Big Bang Theory
The Big Bang is an idealization, a
simplified description (analogous to the
approximation of the Earth as a perfect sphere),
and cosmologists are now occupied with mapping
out/filling in the details. Even so, certain
basic elements of the model remain to be
understood e.g., the natures of the Dark Matter
Dark Energy which together make up 95 of the
mass-energy of the Universe These puzzles do
NOT mean that the Big Bang Theory is
wrongrather, it provides the framework for
investigating them.
33
The Big Bang TheoryAre there human implications?
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36
(as seen on public buses and roadside billboards)
37
Spectrum of Light from Galaxies Redshift of
Galaxy Emission Absorption Lines recession vel
ocity v/c z ??/?0 (approximation for objects
moving with v/c ltlt 1)
receding slowly
?
receding quickly
38
Hubble Space Telescope in Orbit Measured distanc
es to galaxies using Cepheid Variable stars
39
Hubble (1929)
Hubble Space Telescope (2000)
40
Modern Hubble Diagram Extend to larger
distances using objects brighter than
Cepheids
41
The Microwave Sky The Universe is filled with
thermal radiation Cosmic Microwave Background
(CMB) COBE Map of the Temperature of the
Universe On large scales, the Universe is
(nearly) isotropic around us (the same in all
directions) CMB radiation probes as deeply as we
can, far beyond optical light from galaxies
snapshot of the young Universe (at 400,000 years
old)
T 2.7 degrees above absolute zero
Scale of the Observable Universe Size 1028
cm Mass 1023 Msun
42
CMB
(nearly) isotropic
Earth
not
43
The Cosmological Principle
A working assumption (hypothesis) aka the
Copernican Principle We are not priviledged
observers at a special place in the
Universe At any instant of time, the Universe
should appear
ISOTROPIC (over large scales) to
All observers. A Universe that appears isotropic
to all observers is
HOMOGENEOUS i.e., the same at every
location (averaged over large scales).
44
The Microwave Sky COBE Map of the Temperature
of the Universe Dipole anisotropy due to our
Galaxys motion through the Universe
T 2.728 deg above absolute zero
Red 2.70.001 Blue2.7-0.001
Red 2.70.00001 deg Blue 2.7-0.00001 deg
45
The Microwave Sky COBE Map of the Temperature
of the Universe Map with Dipole
anisotropy removed fluctuations of the density
of the Universe (plus Galactic emission)
T 2.7 degrees above absolute zero
Red 2.70.001 Blue2.7-0.001
Red 2.70.00001 deg Blue 2.7-0.00001 deg
46
Cosmology as Metaphor From The New Yorker,
March 5, 2001 A hiss of chronic corruption
suffuses the capital like background radiation
from the big bang.
--Hendrik Hertzberg
The Talk
of the Town
47
Physical Implications of Expanding Universe
An expanding gas cools and becomes less dense as
it expands. Run the expansion backward
going back into the past, the Universe
heats up and becomes denser. Expanding Universe
plus known laws of physics imply the
Universe has finite age and a singular
(nearly infinite density and Temperature)
beginning about 14 Billion years ago
THE BIG BANG
48
Big Bang Nucleosynthesis
Origin of the Light Elements Helium, Deuterium,
Lithium, When the Universe was younger than
about 1 minute old, with a Temperature above
1 billion degees, atomic nuclei (e.g., He4
nucleus 2 neutrons 2 protons bound
together) could not survive instead the baryons
formed a soup of protons neutrons. As
the Temperature dropped below this value (set by
the binding energy of light nuclei), protons
and neutrons began to fuse together to form
bound nuclei the light elements were
synthesized as the Universe expanded and
cooled.
49
BBN predicted abundances
h H0/(100 km/sec/Mpc)
Fraction of baryonic mass in He4
Light Element abundances depend mainly on
the density of baryons in the Universe
Deuterium to Hydrogen ratio Lithium to
Hydrogen ratio
baryon/photon ratio
50
BBN Theory vs. Observations Observational
constraints shown as boxes Remarkable agreement
over 10 orders of magnitude in abundance
variation Concordance region ?b
0.04 Strongest constraint comes from
Deuterium. Excellent agreement w/ more recent
CMB measurements
?b
4He
51
Recent CMB experiments Going to
smaller angular scales ?? higher resolution
52
Recent CMB Anisotropy Experiments South Pole
Boomerang
DASI
53
CMB Angular Power Spectrum
Angular power spectrum is a statistical way to
characterize the spatial structure in a
2-dimensional image or map
54
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56
  • Oscillation of the Photon-
  • Baryon fluid when the
  • Universe was 400,000 yrs old
  • Imprint on the Microwave
  • sky


57
Theoretical dependence of CMB anisotropy on the
baryon density
Angular frequency
Angular separation on the sky
58
Microwave Background AnisotropyProbes Wb
(Baryon Density)
Wb 0.04
  • Boomerang experiment (2001)

DASI experiment (2001)
59
Einsteins General Relativity
Matter and Energy curve
Space-Time All bodies move in this
curved Space-time
A massive star attracts nearby objects by
distorting spacetime
60
Gravity Newton vs. Einstein
Newton 1) gravitation is a force exerted by one
massive body on another.
2) a body acted on by a force
accelerates Einstein 1) gravitation is the
curvature of spacetime due to a
nearby massive body (or any form of energy)
2) a body follows the straightest
possible path (aka geodesic)
in curved spacetime
61
Einstein space can also be globally curved
What is the geometry of three-dimensional space?
62
Microwave photons traverse a significant
fraction of the Universe, so they can probe
its spatial curvature Sizes of hot and cold
spots in the CMB give information on curvature
of space In curved space, light bends as it
travels fixed object has larger angular size in
a positively curved space CMB spots appear
larger. Opposite occurs for negatively curved
space.
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Position of first Peak probes the
spatial Curvature of the Universe
65
Microwave Background AnisotropyProbes Spatial
Curvature
W0 1.03 0.06
W0 1.04 0.06
  • Boomerang experiment (2001)

DASI experiment (2001)
66
Einstein space can also be globally curved
What is the geometry of space? Recent
observations of the Microwave background
anisotropy indicate it is flat
67
Probes of the Matter Density Wm
  • Current evidence

From galaxy clusters and other probes
Wm 0.3
Galaxy kinematics
Lensing
X-ray gas
68
rotation velocity
Observed flat, M d
Keplerian v d-1/2
blueshift
redshift
Typical rotation speed 200 km/sec and visible
disk size 10 kpc
69
Clusters of Galaxies Size 1025 cm Megaparsec
(Mpc) Mass 1015 Msun Largest
gravitationally bound objects galaxies, gas,
dark matter
70
The 2 Dark Matter Problems
Observations indicate ?visible matter 0.01
?baryons 0.04 ?dark matter 0.3
BBNCMB
Dark Baryonic matter composed of protons,
neutrons, (more fundamentally of quarks)
Dominant component of Dark Matter is
Non-baryonic requires a new component beyond
quarks,...
71
Basic Dark Matter Questions
How much is there? What is the value of ??
Current evidence suggests 0.3. Where is it?
Is it just clustered with the luminous material?
Not precisely, since Dark halos extend beyond
luminous galaxies. Are there completely dark
galaxies or clusters? What is it? BBNCMB ?
mostly not made of baryons (i.e., protons,
neutrons, quarks, etc). It could be a new Weakly
Interacting Massive Particle (WIMP).
Supersymmetry models predict these. Ultimate
Copernican principle Were not even made of
the central stuff of the Universe!
72
Dark Energy and the Accelerating Universe
Brightness of distant Type Ia supernovae
indicates the expansion of the Universe is
accelerating, not decelerating. If General
Relativity is valid, this requires a new form of
stuff with negative effective pressure
DARK ENERGY Characteriz
e by its equation of state w p/? more
specifically, p lt ???? (w lt ?1/3)
Dubya
pressure
density
73
p ?? (w ?1)
Accelerating
Empty
SNe Ia CMB indicate ?m ? 0.3 ?DE ? 0.7
Size of the Universe
Open
Closed
Today
Cosmic Time
74
Evidence for Dark Energy
  • Direct Evidence for Acceleration
  • Brightness of distant Type Ia
    supernovae
  • Standard candles ? measure
    luminosity distance dL(z)
  • sensitive to the expansion history
    H(z)
  • Supernova Cosmology Project
  • High-Z Supernova Team
  • II. Evidence for Missing Energy
  • CMB? Flat Universe ?0 1
  • Clusters, LSS ? Low matter density
    ?m ? 0.3
  • ?missing 1 0.3 0.7 and
    missing stuff can only
  • dominate recently for structure to
    form w lt 0.5

75
Discovery of SNe Ia at high redshift z 0.5
1
76
Type Ia Supernovae Peak Brightness as a
calibrated Standard Candle Intrinsic
Brightness vs. Time Physical model White dwarf
star, accreting mass from a companion star,
explodes when it exceeds a critical mass
(Chandrasekhar)
Luminosity
Time
77
42 SNe Ia
Fainter
Apparent Brightness
distance
m(z) M5log(H0dL)(1z) ? dz/H(z)
78
CMB and Supernovae
  • CMB SNIa
  • orthogonal constraints

Dark Energy density
Wm 0.31 0.13 WL 0.71 0.11
Dark matter density
79
The Early Universethe key to Large-scale
Structure
From our vantage point 13 billion years after the
Big Bang, we are now trying to unravel what
happened in the earliest tiny fraction of a
second, when the Universe was 0.0000000000000000
00000000000000000001 seconds old! We can test
our ideas about the Very Early Universe by
observing the distributions of galaxies and of
cosmic radiations in space.This has been a major
breakthrough in cosmology over the last decade.
80
Inflation
An epoch of very rapid expansion, during which
the size of the Universe grows faster than
time This means that comoving observers appear
to be accelerating away from each other. As
we saw, there is mounting evidence (from Type Ia
Supernovae) that the Universe recently (10
billion years ago) entered such an
accelerating phase of expansion. The Universe
may now be in the early stages of Inflation.
81
Inflation in the Early Universe
A hypothetical epoch of very rapid
(accelerated) expansion very early in
cosmic history (perhaps around t 10-33
seconds), during which the size of the Universe
grew faster than time. If this period of
Superluminal expansion lasts long enough,
then it effectively stretches any inhomogeneity
space curvature, explaining why the
Universe today appears homogeneous and
flat. Theory arose in 1980 (A. Guth) from
considerations of symmetry-breaking phase
transitions in Grand Unified Theories.
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Inflation Models Scalar Field slowly rolls down
a hill
Potential energy density
High Temp.
High Temperature Symmetry is restored, ?
0. Low Temperature Symmetry is broken ?
or -
Low Temperature
field
Potential energy function must be fairly flat
so the field rolls slowly probably not a Higgs
field, must be something else
84
After rolling down, scalar field oscillates
around the bottom? REHEATING
Potential energy density
High Temp.
High Temperature Symmetry is restored, ?
0. Low Temperature Symmetry is broken ?
or -
Low Temperature
?
field
At the end of inflation, the Universe is very
cold.
Reheating Oscillating field energy transformed
to other particles as it decays Universe heats
back up to high Temperature another bang that
creates all the matter and energy in the Universe.
85
Who is the inflaton field?
Originally it was thought a GUT Higgs field would
do the trick. With the death of old
inflation, this hope dimmed. Inflation requires
a new scalar field with a very flat potential
energy function. Currently, there is no
consensus among particle physics theorists as to
the identity of this hypothesized inflaton
field. Inflation has thus been described as a
theory in search of a model.
86
Density Perturbations Structure
Inflation provides a physical mechanism for
producing the initial seed perturbations
which grew into Large-scale Structure Density
Perturbations from Quantum Mechanics Classically
, the scalar field rolls down its potential at
the same speed everywhere in the Universe ?
?(t). According to Quantum Mechanics, the
amplitude (or rolling speed) of the field
fluctuates it differs from place to place by a
small amount, ? ?(x,t). These field
fluctuations imply spatial fluctuations in
the energy density of the Universe. During,
reheating, these become fluctuations in the
density of all matter radiation particles.
This is a crucial but originally unforeseen
consequence of the theory, now seen to be in
excellent agreement with CMB observations.
87
1-dimensional cross-section
space
field
field
88
Evidence for Inflation
  • Large-scale homogeneity and isotropy (by design)
  • Spatial flatness (Euclidean) ?total 1
  • (Power) Spectrum of density perturbations
    inferred
  • from CMB experiments agrees to high precision
  • with spectrum of quantum fluctuations
    predicted by inflation
  • Future
  • -more precise measurements by satellites (MAP,
    Planck)
  • -measurement of CMB polarization? possibly
    test inflationary
  • prediction for gravity wave spectrum and
    distinguish
  • between different inflation models

89
The Structure Formation Cookbook
  • Initial Conditions Start with a Theory for the
    Origin of
  • Density Perturbations in the Early
    Universe
  • Your Favorite Inflation model
  • 2. Cooking with Gravity Growing Perturbations to
    Form Structure
  • Set the Oven to Cold, Hot, or Warm Dark
    Matter
  • Season with a few Baryons and add Dark
    Energy
  • 3. Let Cool for 14 Billion years (or buy a Really
    Big Computer)
  • 4. If it looks, smells, and tastes like the real
    thing, then publish the recipe. If not, publish
    anyway, and then start over with different
    ingredients or change the oven settings.


90
Early
Evolution of Structure in a Simulated Big
Bang Universe Filled with Dark Matter The
Cosmic Web Galaxies and Clusters form at the
intersections of sheets and filaments, very
similar to the Structure seen in galaxy surveys
Today
91
Evolution of Structure in the Universe
92
SDSS 2.5 meter Telescope
93
Galaxy Clustering in the SDSS Redshift Survey
100,000 galaxies Voids, sheets, filaments
94
Probing Neutrino Mass and Baryon Density
Wiggles Due to Non-zero Baryon Density
SDSS MAP will constrain sum of stable neutrino
masses as low as 0.5 eV
95
Some Key Questions for 21st Century Cosmology
How did the hierarchy of large-scale structure,
from stars to galaxies to clusters and beyond,
originate? Did this structure arise from the
expansion stretching of microscopic quantum
ripples in the fabric of spacetime during the
earliest moments of the Big Bang, a theory known
as Cosmic Inflation? What is the nature of the
Dark Matter that makes up most of the mass of the
Universe? Is it in the form of exotic elementary
particles as yet undiscovered? (The Ultimate
Copernican Principle) What is the nature of the
Dark Energy that is causing the expansion of the
Universe to Accelerate? Will the Universe
continue to accelerate forever? What happened
before the Big Bang? Is this question
meaningful? Are there more than 3 spatial
dimensions? Can we ever detect them?

96
CMB Sky 1992 circa Jan. 2003
97
MAP Satellite launched June 2001 Planck
Satellite planned for 2008
98
Proposed satellite mission to observe several
thousand SNe Ia out to z 1.7
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Despite major recent advances in cosmology,
fundamental mysteries remain
Unlike the ancient mystics, however, we hope
these unexplained phenomena can in principle be
understood, by a combination of new theoretical
insight and experimental advances scientists are
perpetual optimists. So far, this optimism has
been justified by the continued progress of
science. What are the ultimate limits to our
understanding of the Universe?

101
References
T. Ferris, The Whole Shebang (Touchstone Books
1997) B. Greene, The Elegant Universe (Vintage,
1999) A. Guth and A. Lightman, The Inflationary
Universe J. Silk, A Short History of the
Universe C. Hogan, The Little Book of the Big
Bang More advanced A. Liddle, An Introduction
to Modern Cosmology E. Linder, First Principles
of Cosmology
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