Dark Energy and the Dynamics of the Universe Eric Linder Lawrence Berkeley National Laboratory
Uphill to the Universe Steep hills: Building up - Eroding away -
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.
Our Expanding Universe Bertschinger & Ma ; courtesy Ma
Our Cosmic Address 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. Earth 107 meters Solar system 1013 m Milky Way galaxy 1021 m Local Group of galaxies 3x1022 m Local Supercluster of galaxies 1024 m The Visible Universe 1026 m
The Cosmic Calendar Inflation1016 GeV Quarks Hadrons1 GeV Nuclei form1 MeV Atoms form1 eV [Room temperature 1/40 eV] Stars and galaxies first form:1/40 eV Today:1/4000 eV
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
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.
Acceleration and Dark Energy Einstein says gravitating mass depends on energy-momentum tensor: both energy density and pressurep,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 can accelerate the expansion .. ..
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.
cf. Tonry et al. (2003) accelerating accelerating decelerating decelerating Cosmic Concordance • Supernovae aloneAccelerating 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!
Dark Energy Is... Dark Energy Is!!! • 70-75% of the energy density of the universe • Accelerating the expansion, like inflation at 10-35s • Determining the fate of the universe ! 70-75% of the energy density of the universe 95% of the universe unknown! ! Accelerating the expansion, 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 !
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.
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.
Cosmic Coincidence Size=2 Size=1/4 Size=1/2 Size=4 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 Today
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
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, & Marion2003
Standardized Candle Brightness Time after explosion Brightness tells us distance away (lookback time) Redshift measured tells us expansion factor (average distance between galaxies)
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 M and L Dark Energy Properties Redshift & SN Properties Spectra data analysis physics
Weighing the Universe accelerating decelerating
Cosmic Concordance cf. Tonry et al. (2003) accelerating decelerating
Nature of Dark Energy “Stretchiness” (EOS) Matter Density
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(Knop et al. 2003)[SN+LSS+CMB] wconst= -1.08+0.18-0.20?(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 0.6 1.0 0.4 0.8 0.2 redshift z 10 billion years
Supernova Properties Astrophysics Understanding Supernovae Nearby Supernova Factory G. Aldering (LBL) Cleanly understood astrophysics leads to cosmology
High Redshift Supernovae Discover Reference Subtract-->SN! Riess et al./STScI
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!
Dark Energy – The Next Generation Dedicated dark energy probe SNAP: Supernova/Acceleration Probe
Design a Space Mission HDF GOODS wide 9000 the Hubble Deep Field plus 1/2 Million HDF • Redshifts z=0-1.7 • Exploring the last 10 billion years • 70% of the age of the universe deep colorful Both optical and infrared wavelengths to see thru dust.
Astronomical Imaging Focus star projectors Guider Visible NIR Spectrograph port Calibration projectors Half billion pixel array 36 optical CCDs 36 near infrared detectors JWST Field of View Larger than any camera yet constructed
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
Astrophysical Uncertainties For accurate and precision cosmology, need to identify and control systematic uncertainties.
Weighing Dark Energy SN Target
Exploring Dark Energy Needed data quality Dark energy theories Current ground based compared with Binned simulated data and a sample of Dark energy models
The Fate of Our Universe Size of Universe Fate History 0 Future Age of Universe Looking back 10 billion years to look forward 40 billion
Frontiers of the Universe Size of Universe Fate History 0 Future Age of 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? Uphill to the Universe!
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
Cosmic Archaeology Supernovae: direct probe of cosmic expansion Time: 30-100% of present age of universe (When you were 12-40 years old) Cosmic matter structures: less direct probes of expansion Pattern of ripples, clumping in space, growing in time. 3D survey of galaxies and clusters. 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!)