1 1 The Darkness of the Universe: The Darkness of the Universe: Mapping Expansion and Growth Eric Linder Lawrence Berkeley National Laboratory

2 2 Discovery! Acceleration

3 3 Exploring Dark Energy First Principles of Cosmology E.V. Linder (Addison- Wesley 1997)

4 4 Fundamental Physics Astrophysics  Cosmology  Field Theory a(t)  Equation of state w(z)  V(  ) V (  ( a(t) ) ) SN CMB LSS Map the expansion history of the universe The subtle slowing and growth of scales with time – a(t) – map out the cosmic history like tree rings map out the Earth’s climate history. STScI

5 5 Standard Candles Brightness tells us distance away (lookback time) Redshift measured tells us expansion factor (average distance between galaxies)

6 6 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

7 7 Standardized Candle Redshift tells us the expansion factor a Time after explosion Brightness Brightness tells us distance away (lookback time t)

8 8 Standardized Candle Wang et al. 2003, ApJ 590, 944 Color vs. Magnitude -- “HR” diagram CMAGIC New method: Physics based Less dispersion (4% in distance?) Less sensitive to systematics from dust extinction

9 9 Images Spectra Redshift & SN Properties dataanalysisphysics Nature of Dark Energy Each supernova is “sending” us a rich stream of information about itself. What makes SN measurement special? Control of systematic uncertainties

10 ~2000 SNe Ia 10 billion years Hubble Diagram redshift z  brightness (expansion)

11 Nearby Supernova Factory Understanding Supernovae Cleanly understood astrophysics leads to cosmology Supernova Properties Astrophysics G. Aldering (LBL)

12 Looking Back 10 Billion Years STScI

13 Looking Back 10 Billion Years STScI

14 Looking Back 10 Billion Years 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! STScI

15 Dark Energy – The Next Generation SNAP: Supernova/Acceleration Probe Dedicated dark energy probe

16 Design a Space Mission colorfulcolorful wide GOODS HDF 9000  the Hubble Deep Field plus 1/2 Million  HDF deep Redshifts z=0-1.7 Exploring the last 10 billion years 70% of the age of the universe Both optical and infrared wavelengths to see thru dust.

17 Controlling Systematics Same SN, Different z  Cosmology Same z, Different SN  Systematics Control

18 Our Tools Expansion rate of the universe a(t) ds 2 =  dt 2 +a 2 (t)[dr 2 /(1-kr 2 )+r 2 d  2 ] Einstein equation (å/a) 2 = H 2 = (8  /3)  m +  H 2 (z) = (8  /3)  m + C exp{  dlna [1+w(z)]} Growth rate of density fluctuations g(z) = (  m /  m )/a Poisson equation  2  (a)=4  Ga 2  m = 4  G  m (0) g(a)

19 Cosmic Background Radiation 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. Snapshot of universe at 380,000 years old, when 1/1100 size now Planck satellite (2007) WMAP/ NASA

20 Complementarity SN+CMB have excellent complementarity, equal to a prior  (  M )  Frieman, Huterer, Linder, & Turner 2003 SN+CMB can detect time variation w´ at 99% cl (e.g. SUGRA). Supernovae tightly constrain dark energy models… And play well with others. =w a /2 Present value of “negativity” Time variation

21 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.

22 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

23 Gravitational Lensing “Galaxy wallpaper” Lensing by (dark) matter along the line of sight N. Kaiser

24 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.

25 Weak Lensing - Shear More area, less source density, shallower sources, e.g Ground Less area, more source density, deeper sources, e.g. Space  Large scalesSmall scales  Error in shear estimation statistics only! 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 systematics

26 Weak Lensing - Cosmography 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 Jain and Taylor 2003, Bernstein and Jain 2004, Zheng, Hui, & Stebbins 2004, Hu and Jain 2004

27 Supernovae + Weak Lensing Comprehensive: no external priors required! Independent test of flatness to 1-2% Complementary: w 0 to 5%, w to 0.11 (with systematics) Flexible: if systematics allow, can cover deg 2 √ Bernstein, Huterer, Linder, & Takada

28 Linear Structure: Baryon Oscillations The same primordial imprints in the photon field show up in matter density fluctuations. Eisenstein 2002 Galaxy cluster size Hubble horizon today Matter Power Spectrum Since the photons and baryons are tightly coupled until z<1100, there are baryon “acoustic oscillations”, submerged amid dark matter.

29 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 z=1-2 - Require large, deep, accurate galaxy redshift surveys (millions of galaxies, thousand(s) of square degrees) - Possibly KAOS+SNAP or SNAP H  survey - Complementary with SN if dark energy dynamic

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32 Exploring the Unknown 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 When you have a mystery ailment, you want a diagnosis with blood tests, EKG, MRI,...