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Dark Energy and the Dynamics of the Universe Eric Linder Lawrence Berkeley National Laboratory 11 Uphill to the Universe Steep hills: Building up Eroding away - 22 Start Asking Why, and... There is no division between the human world and cosmology, between physics and astrophysics. ... ... Everything is dynamic, all the way to the expansion of the universe. 33 Our Expanding Universe QuickTime™ and a YUV420 codec decompressor are needed to see this picture. Bertschinger & Ma ; courtesy Ma 44 Our Cosmic Address Earth 107 meters Solar system 1013 m Our Sun is one of 400 billion stars in the Milky Way galaxy, which is one of more than 100 billion galaxies in the visible universe. Milky Way galaxy 1021 m Local Group of galaxies 3x1022 m Local Supercluster of galaxies 1024 m The Visible Universe 1026 m 55 The Cosmic Calendar Inflation 1016 GeV Quarks Hadrons 1 GeV Nuclei form 1 MeV Atoms form 1 eV [Room temperature 1/40 eV] Stars and galaxies first form: 1/40 eV Today: 1/4000 eV 66 Mapping Our History The subtle slowing down and speeding up of the expansion, of distances with time: a(t), maps out cosmic history like tree rings map out the Earth’s climate history. STScI 77 Discovery! Acceleration data from Supernova Cosmology Project (LBL) graphic by Barnett, Linder, Perlmutter & Smoot (for OSTP) Exploding stars – supernovae – are bright beacons that allow us to measure precisely the expansion over the last 10 billion years. 88 Acceleration and Dark Energy Einstein says gravitating mass depends on energy-momentum tensor: both energy density and pressure p, as +3p Negative pressure can give negative “mass” Newton’s 2nd .. law: Acceleration = Force / mass R = - (4/3)G R .. Einstein/Friedmann equation: a = - (4/3)G (+3p) a Negative pressure Relation between and p (equation of state) is crucial: w=p/ Acceleration possible for p < -(1/3) or w < -1/3 What does negative pressure mean? Consider 1st law of thermodynamics: dU = -p dV But for a spring dU = +k xdx or a rubber band dU = +T dl Vacuum Energy Quantum physics predicts that the very structure of the vacuum should act like springs. Space has a “stretchiness”, or tension, or vacuum energy with negative pressure. Review -Einstein: expansion acceleration depends on +3p Thermodynamics: pressure p can be negative Quantum Physics: vacuum energy has negative p “Tree ring” markers can map the expansion history, measure acceleration, detect vacuum energy. Cosmic Concordance cf. Tonry et al. (2003) • Supernovae alone Accelerating expansion >0 • CMB (plus LSS) Flat universe >0 • Any two of SN, CMB, LSS Dark energy ~75% Frontiers of Cosmology Us STScI 95% of the universe is unknown! 13 13 Dark Is!!! DarkEnergy Energy Is... !• 70-75% of the energy density of the universe • Accelerating 95%the of the expansion, universelike unknown! inflation at 10-35s !• Accelerating Determining the the fate expansion, of the universe like inflation at 10-35s Repulsive gravity! ! Determining the fate of the universe Fate of the universe! Is this mysterious dark energy the original cosmological constant , a quantum zeropoint sea? What’s the Matter with Energy? Why not just bring back the cosmological constant ()? When physicists calculate how big should be, they don’t quite get it right. Sum of zeropoint energy modes: /8G = <0> ~ h/2 d3k (k2+m2) ~ kmax4 If Planck energy cutoff, <0> ~ c5/G2h ~ 1076 GeV4 -- If kmax~ QCD cutoff, 10-3 GeV4 -- But need 10-47 GeV4 ! 15 15 What’s the Matter with Energy? They are off by a factor of 1,000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000. 16 16 What’s the Matter with Energy? This is modestly called the fine tuning problem. But it gets worse: because the cosmological constant is constant, it is the same throughout the history of the universe. Why didn’t it take over the expansion billions of years ago, before galaxies (and us) had the chance to form? Or why didn’t it wait until the far future, so today we would never have detected it? This is called the coincidence problem. 17 17 Cosmic Coincidence Think of the energy in as the level of the quantum “sea”. At most times in history, matter is either drowned or dry. Dark energy Matter Size=1/4 Size=1/2 Today Size=2 Size=4 Key Issue for Physics Today The universe is not simple: So maybe neither is the quantum vacuum (or gravitation)? On Beyond ! On beyond ! It’s high time you were shown That you really don’t know all there is to be known. -- à la Dr. Seuss, On Beyond Zebra We need to explore further frontiers in high energy physics, gravitation, and cosmology. New quantum physics? Quintessence (atomic particles, light, neutrinos, dark matter, and…), Dynamical vacuum New gravitational physics? Quantum gravity, supergravity, extra dimensions? We need new, highly precise data 20 20 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 SCP Insensitive to initial conditions: “Stellar amnesia” Höflich, Gerardy, Linder, & Marion 2003 QuickTime™ and a YUV420 codec decompressor are needed to see this picture. Standardized Candle Brightness Time after explosion Brightness tells us distance away (lookback time) Redshift measured tells us expansion factor (average distance between galaxies) 22 22 What makes SN measurement special? Control of systematic uncertainties At every moment in the explosion event, each individual supernova is “sending” us a rich stream of information about its internal physical state. Lightcurve & Peak Brightness Images Redshift & SN Properties M and Dark Energy Properties Spectra data analysis physics History & Fate 24 24 Weighing the Universe 25 25 Cosmic Concordance cf. Tonry et al. (2003) 26 26 “Stretchiness” (EOS) Nature of Dark Energy Matter Density 27 27 What We Know “ ‘Most embarrassing observation in physics’ – that’s the only quick thing I can say about dark energy that’s also true.” -- Edward Witten Dark energy causes acceleration -- “negative gravity” -- through its strongly negative pressure. Define equation of state ratio by w(z)=pressure/(energy density) Today’s state of the art: wconst= -1.05+0.15-0.200.09 wconst= -1.08+0.18-0.20? (Knop et al. 2003) [SN+LSS+CMB] (Riess et al. 2004) [SN+LSS+CMB] But what about dynamics? Generically expect time variation w What We (Don’t) Know Assuming w is constant can be deceiving, even to test if dark energy is a cosmological constant . If we don’t look hard for the time variation w then we don’t learn the physics! We have to do it right. • Longer “lever arm” (higher redshift, more history) • Many more supernovae, more precisely • High accuracy Hubble Diagram ~2000 SNe Ia 10 billion years 0.2 0.4 0.6 0.8 1.0 redshift z 30 30 Understanding Supernovae Nearby Supernova Factory G. Aldering (LBL) Supernova Properties Astrophysics Cleanly understood astrophysics leads to cosmology 31 31 High Redshift Supernovae Discover Reference Subtract-->SN! Riess et al./STScI 32 32 Looking Back 10 Billion Years STScI 33 33 Looking Back 10 Billion Years QuickTime™ and a YUV420 codec decompressor are needed to see this picture. 34 34 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! 35 35 Dark Energy – The Next Generation Dedicated dark energy probe SNAP: Supernova/Acceleration Probe 36 36 Design a Space Mission 9000 the Hubble Deep Field wide plus 1/2 Million HDF HDF deep GOODS • Redshifts z=0-1.7 • Exploring the last 10 billion years • 70% of the age of the universe colorful Both optical and infrared wavelengths to see thru dust. 37 37 Astronomical Imaging Focus star projectors Half billion pixel array 36 optical CCDs 36 near infrared detectors Guider Visible NIR JWST Field of View Spectrograph port Calibration projectors Larger than any camera yet constructed 38 38 New Technology CCD’s • New kind of CCD detector developed at LBNL • Radiation hard for space ; High efficiency • Able to be combined into large arrays 39 39 Astrophysical Uncertainties For accurate and precision cosmology, need to identify and control systematic uncertainties. Systematic Control Host-galaxy dust extinction Wavelength-dependent absorption identified with high S/N multiband photometry. Supernova evolution Supernova subclassified with high S/N light curves and peakbrightness spectrum. Flux calibration error Program to construct a set of 1% error flux standard stars. Malmquist bias Supernova discovered early with high S/N multi-band photometry. K-correction Construction of a library of supernova spectra. Gravitational lensing Measure the average flux for a large number of supernovae in each redshift bin. Non-Type Ia contamination Classification of each event with a peak-brightness spectrum. 40 40 SN Population Drift 41 41 Controlling Systematics 42 42 Weighing Dark Energy SN Target 43 43 Exploring Dark Energy Current ground based compared with Binned simulated data and a sample of Dark energy models Dark energy theories Needed data quality 44 44 The Fate of Our Universe Size of Universe Looking back 10 billion years to look forward 40 billion Fate History 0 Future Age of Universe 45 45 Frontiers of the Universe What is dark energy? Will the universe expansion accelerate forever? Does the vacuum decay? Phase transitions? How many dimensions are there? How are quantum physics and gravity unified? What is the fate of the universe? Size of Universe Fate History 0 Uphill to the Universe! Future Age of Universe 46 46 The Next Physics The Standard Model gives us commanding knowledge about physics -- 5% of the universe (or 50% of its age). That 5% contains two fundamental forces and 57 elementary particles. What will we learn from the dark sector?! How can we not seek to find out? Frontiers of Science Let’s find out! 1919 1998 Breakthrough of the Year 2003 The Next Physics Cosmic Archaeology CMB: direct probe of quantum fluctuations Time: 0.003% of the present age of the universe. (When you were 0.003% of your present age, you were a 2 celled embryo!) Cosmic matter structures: less direct probes of expansion Pattern of ripples, clumping in space, growing in time. 3D survey of galaxies and Supernovae: direct probe of cosmic expansion Time: 30-100% of present age of universe (When you were 12-40 years old) 50 50 Cosmic Background Radiation WMAP/ NASA Photon density 407±0.4 cm-3 Baryon density bh2=0.023±0.001 Snapshot of universe at 380,000 years old, 1/1100 the size Planck satellite (2007) nb/n=6 x 10-10 ; consistent with primordial nucleosynthesis Matter-antimatter asymmetry? Baryogenesis? 51 51 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 52 52 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. 53 53 Fundamental Physics Astrophysics SN CMB LSS a(t) Cosmology Equation of state w(z) Field Theory V() V ( ( a(t) ) ) 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. Map the expansion history of the universe STScI Cosmic Archaeology Inflation sets seeds of structure, patterning both radiation (CMB) and matter (galaxies) CMB } NASA GSFC/COBE Large scale structure, Dark Energy, Acceleration