The Darkness of the Universe:

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The Darkness of the Universe Mapping
Expansion and Growth
Eric Linder Lawrence Berkeley National Laboratory
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Discovery! Acceleration
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Exploring Dark Energy
First Principles of Cosmology E.V. Linder
(Addison-Wesley 1997)
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Fundamental Physics
The subtle slowing and growth of scales with time
a(t) map out the cosmic history like tree
rings map out the Earths climate history.
STScI
Map the expansion history of the universe
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Standard Candles
Brightness tells us distance away (lookback
time) Redshift measured tells us expansion
factor (average distance between galaxies)
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Type Ia Supernovae

• Exploding star, briefly as bright as an entire
  galaxy
• Characterized by no Hydrogen, but with Silicon
• Gains mass from companion until undergoes
  thermonuclear runaway
• Standard explosion from nuclear physics

Insensitive to initial conditions Stellar
amnesia Höflich, Gerardy, Linder, Marion 2003
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Standardized Candle
Brightness tells us distance away (lookback time
t)
Brightness
Time after explosion
Redshift tells us the expansion factor a
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Standardized Candle
Color vs. Magnitude -- HR diagram
CMAGIC

• New method
• Physics based
• Less dispersion (4 in distance?)
• Less sensitive to systematics from dust
  extinction

Wang et al. 2003, ApJ 590, 944
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What makes SN measurement special? Control of
systematic uncertainties
Each supernova is sending us a rich stream of
information about itself.
Images
Nature of Dark Energy
Redshift SN Properties
Spectra
data
analysis
physics
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Hubble Diagram
? brightness
(expansion)
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Understanding Supernovae
Nearby Supernova Factory
G. Aldering (LBL)
Cleanly understood astrophysics leads to cosmology
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Looking Back 10 Billion Years
STScI
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Looking Back 10 Billion Years
STScI
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Looking Back 10 Billion Years
STScI
To see the most distant supernovae, we must
observe from space. A Hubble Deep Field has
scanned 1/25 millionth of the sky. This is like
meeting 10 people and trying to understand the
complexity of the entire population of the US!
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Dark Energy The Next Generation
Dedicated dark energy probe
SNAP Supernova/Acceleration Probe
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Design a Space Mission
wide
9000? the Hubble Deep Field plus 1/2 Million ? HDF
Redshifts z0-1.7 Exploring the last 10
billion years 70 of the age of the universe
deep
colorful
Both optical and infrared wavelengths to see thru
dust.
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Controlling Systematics
Same SN, Different z ? Cosmology Same z,
Different SN ? Systematics Control
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Our Tools
Expansion rate of the universe a(t) ds2
?dt2a2(t)dr2/(1-kr2)r2d?2 Einstein
equation (å/a)2 H2 (8?/3) ?m ?H2(z)
(8?/3) ?m C exp?dlna 1w(z) Growth
rate of density fluctuations g(z) (??m/?m)/a
Poisson equation ?2?(a)4?Ga2 ??m 4?G?m(0) g(a)
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Cosmic Background Radiation
Snapshot of universe at 380,000 years old, when
1/1100 size now
WMAP/ NASA
Hot and cold spots simultaneously the smallest
and largest objects in the universe single
quantum fluctuations in early universe, spanning
the universe at the time of decoupling.
Planck satellite (2007)
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Complementarity
Supernovae tightly constrain dark energy models
And play well with others.
SNCMB have excellent complementarity, equal to
a prior ?(?M)?0.01. Frieman, Huterer, Linder,
Turner 2003 SNCMB can detect time variation w
at 99 cl (e.g. SUGRA).
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Deceleration and Acceleration
CMB power spectrum measures n-1 and
inflation. Nonzero ISW measures breakdown of
matter domination at early times (radiation) and
late times (dark energy). Large scales (low l)
not precisely measurable due to cosmic variance.
So look for better way to probe decay of
gravitational potentials.
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Gravitational Lensing
Gravity bends light - we can
detect dark matter through its gravity, -
objects are magnified and distorted, -
we can view CAT scans of growth of structure
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Gravitational Lensing
Galaxy wallpaper
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Gravitational Lensing
Lensing measures the mass of clusters of
galaxies. By looking at lensing of sources at
different distances (times), we measure the
growth of mass. Clusters grow by swallowing more
and more galaxies, more mass.
Acceleration - stretching space - shuts off
growth, by keeping galaxies apart. So by
measuring the growth history, lensing can detect
the level of acceleration, the amount of dark
energy.
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Weak Lensing - Shear
Unique suitability of space for weak lensing
? Control of systematics -- Small, stable,
isotropic PSF accurate photo-z ?
Deep survey, area just grows with time, access to
nonlinear mass spectrum (high l)
adapted from C. Vale
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Weak Lensing - Cosmography
Jain and Taylor 2003, Bernstein and Jain 2004,
Zheng, Hui, Stebbins 2004, Hu and Jain 2004

• Identify foreground structures, cross-correlate
  with background slices at various redshifts.
• Removes some systematics
• - Uncorrected PSF shapes average to zero when
  cross-correlated with foreground
• - Non-linear power spectrum form irrelevant so
  information from all scales is useful
• But requires very accurate photometric redshifts

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Supernovae Weak Lensing
Bernstein, Huterer, Linder, Takada

• Comprehensive no external priors required!
• Independent test of flatness to 1-2
• Complementary w0 to 5, w? to 0.11 (with
  systematics)
• Flexible if systematics allow, can cover 10000
  deg2

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Linear Structure Baryon Oscillations
Eisenstein 2002
Matter Power Spectrum
The same primordial imprints in the photon field
show up in matter density fluctuations.
Galaxy cluster size
Hubble horizon today
Since the photons and baryons are tightly coupled
until zlt1100, there are baryon acoustic
oscillations, submerged amid dark matter.
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Structure Growth Linear
Baryon oscillations - Standard ruler we know
the sound horizon by measuring the CMB we
measure the wiggle scale ? geometric distance -
Just like CMB simple, linear physics - But,
only works while mass perturbations linear, so
need to look on very large scales, at z1-2 -
Require large, deep, accurate galaxy redshift
surveys (millions of galaxies, thousand(s) of
square degrees) - Possibly KAOSSNAP or SNAP H?
survey - Complementary with SN if dark energy
dynamic
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Exploring the Unknown
When you have a mystery ailment, you want a
diagnosis with blood tests, EKG, MRI,...
Complementary probes give crosschecks, synergy,
reduced influence of systematics, robust
answers. Space observatory gives multiwavelength
and high redshift measurements, high resolution
and lower systematics. This gives us the
ability to test the framework. Next
The Darkness of the Universe 4 The
Heart of Darkness