1 Dark Matter, Dark Energy and the Fate of the UniverseInto Darkness Dark Matter, Dark Energy and the Fate of the Universe

2 The Ingredients of the Universe: Five Numbers1. The expansion rate 3. The shape of space 2. The Matter-density 4. The deceleration parameter 5. The Cosmological Constant

3 Big Bang Test 1: Redshift-Distance RelationshipHubble Law Expansion 1. The expansion rate Image Credit: Ernest Norcia Observed redshifts of galaxies due to an expansion of the universe. Image Credit: Freedman et al. (2001) Expansion rate (Hubble Constant) + distance gives origin time.

4 12/1/2017 Escape Velocity The greater the initial speed v, the farther it travels before hitting ground. Consider a cannon Even greater speed v=escape If speed v is great enough, the Earth curves out from under cannonball at the same rate as it falls. 2. The Matter-density What is the escape velocity of the universe? Definition: the ratio of the actual density to the critical density to “close” the universe Depends on the mass density of the universe

5 Epochs of the Universe from the CMB to the birth of stars to the modern era

6 Big Bang Test 4: Large Scale StructureBuilding a Universe Observation Big Bang Theory: gives us a way to understand the formation and evolution of Large Scale Structures (LSS) in the universe BB theory says that structures grew from initial density perturbations in CMB Gravitational interaction magnifies initial small perturbations. Put in ingredients of the universe (matter and energy) and build a computer simulation of structure formation from gravity. Sloan Fly-Through of the universe Compare to actual structures.

7 Most of the mass of the universe is dark matterMeasuring the matter density of the universe Most of the mass of the universe is dark matter Argument 1: The speed of rotation of spiral galaxies as a function of radius indicates invisible matter. Redshift of Galaxy along the plane varies (one side rotating towards, the other rotating away.

8 Galaxy Rotation Curves: The speed of rotation of spiral galaxies as a function of radius indicates invisible/dark matter. Velocity curve of stars and beyond is flat or increasing Velocities of planets decrease with distance

9 Argument 2: Random motions of galaxies in clusters indicates dark matter responsible for the large velocities Cluster simulation Large random velocities of galaxies in clusters indicates more matter than is seen.

10 Einstein Cross ObservedArgument 3: Gravitational lensing. Amount of bending of light by gravity indicates hidden mass The images produced by lensing imply a larger lensing mass than can be explained by visible matter. Einstein Cross Model Einstein Cross Observed

11 Bending of light by mass can produce multiple imagesEinstein Ring produced by lensing. Galaxy distorted in a ring is behind the center galaxy causing the distortion.

12 Alternative to Dark Matter: MONDPerhaps dark matter doesn’t exist! But how would you explain the rotation curves of galaxies? Why no drop-off as Newton predicts? Perhaps our theory of motion is wrong. Modify Newton’s Second Law (never been verified for small accelerations) If >1 for small accelerations, it could explain rotation curve.

13 The Smoking Gun: Bullet ClusterBullet Cluster in Optical Wavelengths Cluster in Optical +X-Ray Wavelengths Most of a cluster’s mass is in the hot gas around the cluster (emits X-rays) X-rays show collision between gas in the two clusters

14 Dark Matter in the Bullet ClusterDark matter distribution can be determined using a weak gravitational lensing technique Distortion of background galaxies used to map mass distribution.

15 X-Ray Gas and Dark Matter distribution combinedMost of the mass is not in the galaxies and not in the X-ray gas. It is dark! X-Ray Gas and Dark Matter distribution combined Dark matter is displaced from normal matter (the gas) During the collision, the gas interacted and slowed down, but the dark matter did not. MOND theory predicts no nark matter and therefore no displacement of the two.

16 Dark matter predicts heights of CMB peaksAmount of dark matter affects the relative peak magnitudes in the CMB power spectrum Image Credit: Constaninos Skordis CMB power spectrum from WMAP 5 year data. Fits for MOND (dark line) and ΛCDM (dotted line) are shown

17 What could the Dark Matter Be?Large, dim/invisible objects (MACHO’s) Planets Brown Dwarfs very dim stars neutron stars black holes

18 MAssive Compact Halo Object. (MACHOS) Dark Matter in the halo of our galaxy Brightness of light from Star Macho moving in front of star Halo Microlensing Event observation

19 What could the Dark Matter Be?Subatomic particles Neutrinos Low mass (light) Fast moving (close to the speed of light) very weakly interacting

20 What could the Dark Matter Be?Subatomic particles WIMPS: Weakly Interacting Massive Particles Massive (compared to light neutrino) Slow moving very weakly interacting Examples: Photino, Axion (theoretical particles from particle physics theories. CDMS geranium-silicon detectors look for rare elastic scattering events by Dark matter particles (Soudan mine, Minnesota)

21 Dark Matter and Structure FormationBaryonic (normal matter) perturbations in CMB not enough to explain structure formation Seeds of structure must come from an extra matter component Dark Matter Must collapse against expanding universe

22 Structure seen in the 2dF Galaxy Survey

23 Hot Dark Matter (HDM) Primary form of non-baryonic dark matter moving at extremely high velocity when structures formed. Hot Particles moving near speed of light (relativistic speeds) massive neutrino is prime candidate

24 Structure in an HDM UniverseTop-Down structure formation HDM fills and smooth out the distribution of matter to very large scales fast moving neutrinos travel a long distance before being stopped by gravity Largest structures form first Superclusters Other structures form from “fragmentation” Small structures form last Galaxies

25 Predictions of HDM High density “pancakes” and large empty voidsObserved, but computer models predict voids too empty to match observations Devil is in the details Galaxies form late. No galaxies predicted in early universe Quasars (cores of galaxies) are observed less than 1 Byr after BB Doesn’t match observations

26 Cold Dark Matter WIMP’s (Weakly Interacting Massive Particles) ColdSlow-moving

27 Structures in a CDM UniverseBottom-Up structure formation Since they are massive, they are slow-moving Would only travel a short distance before being stopped by the gravity of the primordial dense region from which it came Smallest structures form first Globular clusters, galaxies Small structures gravitate together, building larger structures Clusters, Superclusters

28 Predictions and Results of CDMSmall dwarf galaxies should be more evenly distributed than massive galaxies Ratio of spirals to dwarfs the same in Superclusters and Voids Does not match prediction Significant mass hidden in Voids No gas clouds seen Some evidence from absorption Lyman-Alpha forest shows intervening matter Computer simulations cannot form superclusters in the time allowed

29 Fate of the Universe Mass-Density determines fate12/1/2017 Mass-Density determines fate  >1  Spherical, closed geometry Universe collapses (Big Crunch)  <1 Hyperbolic, open geometry Universe reaches R= with some velocity remaining  =1  “Flat” Euclidean universe. Exactly the right velocity to continue expanding forever v=0 at time t=

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31 The Ingredients of the Universe: Five Numbers1. The expansion rate 3. The shape of space 2. The Matter-density 4. The deceleration parameter 5. The Cosmological Constant

32 Recall: Ingredient 3: Space CurvatureThe Shape of Space Recall: Ingredient 3: Space Curvature

33 General Relativity in three ideasThere is no such thing as a force of gravity. Mass warps space Effect of geometry on matter=what we used to mean by force Space tells masses how to move In “straight lines” through curved space Image Credit: Mark Garlick / SPL, retrieved from the BBC

34 Observational Confirmation: The Solar Eclipse of 1919

35 The Shape of Space: k. Spots too small or large?Hyperbolic=objects look smaller than expected Spherical=objects look larger than expected Ingredient 3: Space Curvature Flat=objects look just the right size

36 The Planck all sky map of Cosmic Microwave background spotsThe Planck all sky map of Cosmic Microwave background spots. Are they magnified, reduced or “just right”?

37 Image Credit: New ScientistThe effect of the shape of the universe on the predicted sizes of spots on the CMB

38 Sizes of “spots” depends on the curvature: We live in a flat universe!3. The shape of space Boomerang Telescope over Antarctica. Sizes of “spots” depends on the curvature: We live in a flat universe! Planck Result:

39 Fate of the Universe Curvature determines the fate12/1/2017 Curvature determines the fate k=+1  Spherical, closed geometry Universe collapses (Big Crunch) k=-1 Hyperbolic, open geometry Universe reaches R= with some velocity remaining k=0  “Flat” Euclidean universe. Exactly the right velocity to continue expanding forever

40 12/1/2017 Standard Models

41 The Ingredients of the Universe: Five Numbers1. The expansion rate 3. The shape of space 2. The Matter-density 4. The deceleration parameter 5. The Cosmological Constant

42 The Preposterous UniverseIngredient 4: Decleration Parameter

43 Measuring the universe with supernovaeSupernovae can be seen at vast distances. Type IA supernovae from white dwarf collapse are standard candles. Hubble’s law extrapolated across the universe. How much is the universe slowing down due to its own gravity? Supernova 2010lt discovered by Kathryn Gray

44 Supernovae of Type IA Binary pair, where one star becomes a white dwarf Companion red giant’s outer layers can be pulled onto white dwarf Chandrasekar limit= 1.4Msun If material pushes white dwarf over limit, supernova results

45 How are Type IA Supernovae Standard Candles?Always explode at the same mass (the Chandrasekar limit) Therefore always have about the same peak brightness A standard candle: if fainter it must be farther away. Very luminous: Bright as host galaxy for about 2 weeks Can be seen at large distances.

46 Distant supernova can be used to construct a long-range Hubble’s Law; we can measure their redshifts and their distance.

47 Surprise: The Accelerating UniverseDistant supernovae were too faint: they must have accelerated to get to where they are today.

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49 Image Credit: Whittle High-Z Supernova teamThe history and fate of the universe revealed through analysis of supernova light curves

50 Ingredient 2: Mass Density Ingredient 3: Space CurvatureEinstein: matter curves space Gravitational lensing and motion studies reveal the density of dark+visible matter in the universe Matter density from Baryon Acoustic Oscillations in Large Scale Structure. Percival et al Spot sizes on CMB suggests flat universe Conclusion: Even with dark matter, not enough matter in the universe for flat, closed universe Conclusion: The curvature of space is flat

51 Ingredient 4: Decleration Parameter Ingredient 5: Cosmological Constant Type IA supernovae are standard candles Dark energy of empty space is driving acceleration Conclusion: The universe is accelerating implying a cosmological constant / dark energy positive pressure on the universe Accelerating universe needed to explain supernovae

52 CMB flat universe result12/1/2017 Supernova accel. Universe result CMB flat universe result Matter in universe result (measured from motions in galaxy clusters) Image Credit: Supernova Cosmology Project Union 2.1

53 The Accidental Ingredient: ∧0Einstein’s gravity predicts unstable universe. An arbitrary cosmological constant acts as anti-gravity, keeps universe balanced. After Hubble discovered expansion, Einstein called it his greatest blunder. Was it really a mistake? A possible Banksy stencil in San Francisco

54 Toward Non-Standard Models: the Accelerating Universe!

55 The recipe of the universeThe Answer: From the Cosmic Microwave Background (WMAP), we can intuit the percentages of normal matter, dark matter and dark energy.

56 The self-construction of the universe: Dark Matter, Dark Energy, and trivial remainders.Small temperature variations in CMB imply slight variations in density: seeds of structure formation. Today’s universe Early universe Galaxies/clusters CMB Gravity acts on initial perturbations building structures. Dark matter (HDM, CDM varieties) drives structure formation

57 From spots on the Cosmic Microwave Background to the modern universe

58 Sound waves in the early universe leave a signature throughout the universe’s history

59 ¤ - CDM Animation of structure formation12/1/2017 ¤ - CDM Modern simulations are build on the Lambda-CDM model, which combines the effects of dark matter and dark energy. Animation of structure formation Millennium Simulation of 10 billion particles

60 The structures in the universe: observed and simulated (Millennium simulation of 10 billion particles