1 1 Mapping the History and Fate of the Universe DOE Science Colloquium Eric Linder Lawrence Berkeley National Laboratory

2 2 Uphill to the Universe Steep hills: Building up - Eroding away -

3 3 Start Asking Why, and... There is no division between the human world and cosmology Everything is dynamic, all the way to the expansion of the universe.

4 4 Our Expanding Universe Bertschinger & Ma ; courtesy Ma

5 5 Our Cosmic Address Earth 10 7 meters Solar system m Milky Way galaxy m Local Group of galaxies 3x10 22 m Local Supercluster of galaxies m The Visible Universe 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.

6 6 Our Cosmic Calendar Inflation GeV Quarks  Protons 1 GeV Nuclei form 1 MeV Atoms form 1 eV Stars and galaxies first form: 1/40 eV Today: 1/4000 eV [Room temperature 1/40 eV]

7 7 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

8 8 Discovery! Acceleration Exploding stars – supernovae – are bright beacons that allow us to measure precisely the expansion over the last 10 billion years. data from Supernova Cosmology Project (LBL) graphic by Barnett, Linder, Perlmutter & Smoot

9 9 Discovery! Acceleration In 1998, the Supernova Cosmology Project and Hi-Z Team discovered the expansion was speeding up – but gravity pulls things together and should slow the expansion. What is counteracting gravity? Einstein said that energy contributes to mass: E=mc 2

10 Gravitation E=mc 2 Gravity arises from all energy, not just the usual mass. The pressure P of a substance affects the gravity, but this is usually very tiny (because the speed of light c is large, so mc 2 is much bigger than P). But doesn’t this just add to the gravity? Unless the pressure is negative.

11 Negative pressure What does negative pressure mean? When something expands, it usually cools (loses energy). Hot Oven Cool Oven But if you expand (stretch) a spring, it gains energy.

12 Antigravity? Quantum physics predicts that the very structure of spacetime should act like springs. Space has a “stretchiness”. This gives a negative pressure. Add this to the usual mass (galaxies, stars). If there’s enough quantum stuff, it will win out, and the universe will act like the total mass is negative! Is this antigravity? No. No – it’s gravity just as Einstein predicts it, but since it acts like negative mass, it doesn’t bring galaxies together, it pulls them apart.

13 Dark Energy Normal gravity is attractive. This is repulsive. (Not being judgmental, so call it:) Dark Energy Dark energy speeds up the expansion of the universe. By measuring the acceleration using our tree ring (supernova) method, we find that dark energy makes up ~75% of the universe! Because it dominates over the matter contents (which make up only ~25%), dark energy will govern the expansion, and the fate of the universe.

14 95% of the universe is unknown! Frontiers of Cosmology STScI Us

Cosmic Concordance Supernovae alone  Accelerating expansion   > 0 CMB (plus LSS)  Flat universe   > 0 Any two of SN, CMB, LSS  Dark energy ~75% accelerating decelerating cf. Tonry et al. (2003)

16 Dark Energy Is… 75% of the energy density of the universe Accelerating the expansion, like inflation did when the universe was only seconds old Determining the fate of the universe But what is it? Einstein considered something like it when he first invented general relativity. He wanted just enough negative pressure to balance the mass, so the universe would be static. He called it the cosmological constant, but abandoned it later when observations showed the universe was expanding.

17 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. 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.

18 What’s the Matter with Energy? 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. This is modestly called the fine tuning problem.

Cosmic Coincidence? Matter Dark energy Today Size=2 Size=4 Size=1/2Size=1/4 Think of the energy in  as the level of the quantum “sea”. At most times in history, matter is either drowned or dry.

20 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…) 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 Insensitive to initial conditions: “Stellar amnesia” Höflich, Gerardy, Linder, & Marion 2003 SCP

22 Standard Candle Time after explosion Brightness Brightness tells us distance away (lookback time) Redshift measured tells us expansion factor (average distance between galaxies)

23 Supernova “CAT Scan” The energy spectrum of a supernova tells us in fine detail about its origin and properties. Over time the SN atmosphere expands and thins, allowing us to see every layer.

24 History & Fate

25 ~2000 SNe Ia Hubble Diagram redshift z billion years

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

27 Looking Back 10 Billion Years STScI

28 Looking Back 10 Billion Years

29 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!

30 Dark Energy – The Next Generation e.g. SNAP: Supernova/Acceleration Probe Dedicated dark energy probe

31 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 Your life from years old Both optical and infrared wavelengths to see thru dust.

32 Weighing Dark Energy

33 Exploring Dark Energy Current ground based compared with Binned simulated data and a sample of Dark energy models Dark energy theories Needed data quality

34 The History of Our Universe First Principles of Cosmology E.V. Linder (Addison- Wesley 1997)

35 The Fate of Our Universe to look forward 40 billion Looking back 10 billion years Size of Universe History Fate 0 Future Age of Universe

36 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, 1/1100 the size Planck satellite (2007) NASA

37 The Universe: Early and Late Relic imprints of quantum particle creation in inflation - epoch of acceleration at s and energies near the Planck scale (a trillion times higher than in any particle acclerator). These ripples in energy density also occur in matter, as denser and less dense regions. Denser regions get a “head start” and eventually form into galaxies and clusters of galaxies. How quickly they grow depends on the expansion rate of the universe. It’s all connected!

38 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!) Supernovae: direct probe of cosmic expansion Time: % of present age of universe (When you were 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.

39 Geometry of Space WMAP/NASA/Tegmark CMB tells us about the geometry of space - flat? curved? But not much about evolution (snapshot) or dark energy (too early). Escher

40 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

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

42 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.

43 The Next Generation SN Target

44 Fate of the Universe Contemporary Physics Education Project (CPEP)

45 Frontiers of the Universe What is dark energy? Will the universe expansion accelerate forever? Does the vacuum decay? How many dimensions are there? How are quantum physics and gravity unified? What is the fate of the universe? Uphill to the Universe! Size of Universe History Fate 0 Future Age of Universe

Frontiers of Science Breakthrough of the Year Let’s find out!