Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Dark Energy

1,658 views

Published on

A description of dark energy.

Talk for a general audience

Published in: Technology
  • Be the first to comment

Dark Energy

  1. 1. Dark Energy Friday, February 13, 2009
  2. 2. Friday, February 13, 2009
  3. 3. Theory Expansion Supernovae Acceleration Friday, February 13, 2009
  4. 4. Theory Expansion Supernovae Acceleration Friday, February 13, 2009
  5. 5. Friday, February 13, 2009
  6. 6. Einstein’s equation says mass/ energy causes space-time curvature • Curvature = Energy Density Friday, February 13, 2009
  7. 7. What about empty space? Friday, February 13, 2009
  8. 8. What is so special about empty space? Friday, February 13, 2009
  9. 9. What is so special about empty space? Can have curvature even with no matter Friday, February 13, 2009
  10. 10. What is so special about empty space? Can have curvature even with no matter Can have energy in empty space Friday, February 13, 2009
  11. 11. Pressure is related to change in energy in expanding volume Positive pressure does work as it expands -- loses energy and cools Friday, February 13, 2009
  12. 12. Pressure is related to change in energy in expanding volume Positive pressure does work as it expands -- loses energy and cools Friday, February 13, 2009
  13. 13. Positive energy density has negative pressure Λ Λ Λ Λ Λ Λ Λ Volume increased Internal energy increased Pressure is negative Friday, February 13, 2009
  14. 14. In General relativity, pressure causes gravity • Relativity: Space ~ Time • Energy ~ Momentum • Energy density ~ Pressure • T is a mix of pressure and energy density μν • Positive vacuum energy causes anti-gravity Friday, February 13, 2009
  15. 15. Einstein introduced the cosmological constant to allow a static universe “In order to arrive at this consistent view, we admittedly had to introduce an extension of the field equations of gravitation which is not justified by our actual knowledge of gravitation. ... That term is necessary only for the purpose of making possible a quasi-static distribution of matter....” The antigravity from the cosmological constant balances the gravity from matter Disproved by the discovery of the expansion of the universe “My Greatest Blunder” Friday, February 13, 2009
  16. 16. Recap Einstein introduced cosmological constant negative pressure antigravity to allow static universe Friday, February 13, 2009
  17. 17. Theory Expansion Supernovae Acceleration Friday, February 13, 2009
  18. 18. Measure distance in Astronomy by comparing brightness of object to known reference Apparent Magnitude 20 15 Color Friday, February 13, 2009
  19. 19. Measure distance in Astronomy by comparing brightness of object to known reference Du st Apparent Magnitude 20 Distance Modulus 15 Color Bigger apparent magnitude = fainter = farther away Friday, February 13, 2009
  20. 20. Cepheid Variable are a good reference Friday, February 13, 2009
  21. 21. Henrietta Leavitt discovered Cephied Period Luminosity relation Friday, February 13, 2009
  22. 22. Original plates used to discover Cepheids Friday, February 13, 2009
  23. 23. Take negative of one plate Friday, February 13, 2009
  24. 24. Friday, February 13, 2009
  25. 25. Overlap eliminates all but variable star Friday, February 13, 2009
  26. 26. Friday, February 13, 2009
  27. 27. Friday, February 13, 2009
  28. 28. Friday, February 13, 2009
  29. 29. Friday, February 13, 2009
  30. 30. Friday, February 13, 2009
  31. 31. Friday, February 13, 2009
  32. 32. Distance Time Today Friday, February 13, 2009
  33. 33. Distance Time Today Friday, February 13, 2009
  34. 34. Distance Time Today Friday, February 13, 2009
  35. 35. Distance Time Age of the Universe 12 Gya Today Friday, February 13, 2009
  36. 36. Friday, February 13, 2009
  37. 37. HST Hubble Constant Key Project Freedman et al. 2001 Friday, February 13, 2009
  38. 38. Distance Time 12 Gya Today Friday, February 13, 2009
  39. 39. Distance Time 12 Gya Today Friday, February 13, 2009
  40. 40. Distance Time Age of the Universe 12 Gya 10 Gya Today Friday, February 13, 2009
  41. 41. M55 Globular Cluster Friday, February 13, 2009
  42. 42. Distance Time 12 Gya 10 Gya Today Friday, February 13, 2009
  43. 43. Formation of Globular Clusters Distance 13 Gya Time Age of the Universe 12 Gya 10 Gya Today Friday, February 13, 2009
  44. 44. Recap Einstein introduced cosmological constant negative pressure antigravity to allow static universe Cepheid variables used to measure distance (bright, identifiable, known brightness) also used to show expansion of the universe Friday, February 13, 2009
  45. 45. Theory Expansion Supernovae Acceleration Friday, February 13, 2009
  46. 46. Looking for a brighter standard Cepheids are the brightest stars Supernovae are much brighter than cepheids Friday, February 13, 2009
  47. 47. A star is in balance between gravity and pressure Hydrostatic equilibrium Friday, February 13, 2009
  48. 48. When stars are hot, pressure comes from gas pressure PV=NRT Friday, February 13, 2009
  49. 49. When stars are cold, pressure comes from quantum mechanics Cannot put more than two electrons in the same state Electrons must be moving quickly even if cold Friday, February 13, 2009
  50. 50. When stars are cold, pressure comes from quantum mechanics Cannot put more than two electrons in the same state Electrons must be moving quickly even if cold Friday, February 13, 2009
  51. 51. Finite speed of light places a limit on maximum size of core Friday, February 13, 2009
  52. 52. Finite speed of light places a limit on maximum size of core • As core gets heavier, electrons have to move faster to hold it up • Eventually, the speed of light prevents them from moving faster • Core starts to shrink • Gravity gets stronger • Core shrinks faster • Gravity gets stronger Friday, February 13, 2009
  53. 53. Two types of supernovas • Binary white dwarf (Type Ia) • Massive star (Type Ib,c Type II) Friday, February 13, 2009
  54. 54. Friday, February 13, 2009
  55. 55. Type 1a supernovas should be similar • Progenitors have same mass • Formed slowly, history not important • Should have same brightness • Make a good distance estimator Friday, February 13, 2009
  56. 56. Follow up image Friday, February 13, 2009
  57. 57. Friday, February 13, 2009
  58. 58. Friday, February 13, 2009
  59. 59. •Supernovae seen long ago are moving more slowly than they should. •Expansion of universe was less in the past than today •Universe is accelerating Friday, February 13, 2009
  60. 60. Recap Einstein introduced cosmological constant negative pressure antigravity to allow static universe Cepheid variables used to measure distance (bright, identifiable, known brightness) also used to show expansion of the universe Supernovae much brighter than cepheids, can show expansion in distant galaxies. Friday, February 13, 2009
  61. 61. Theory Expansion Supernovae Acceleration Friday, February 13, 2009
  62. 62. Distance Time 12 Gya 10 Gya Today Friday, February 13, 2009
  63. 63. Formation of Globular Clusters Distance 13 Gya Time Age of the Universe 12 Gya 10 Gya Today Friday, February 13, 2009
  64. 64. Expansion History of the Universe s Perlmutter, Physics Today (2003) nd r a xp eve er 0.0001 0.001 fo s 0.01 relative 0.1 1 se lap brightness 1.5 l co Relative to Today's Scale Scale of the Universe 1.0 0 0.25 redshift After inflation, 0.5 ed the expansion either... 0.75 ted rat ra 1 0.5 ele e le cc dec 1.5 a en 2 th , ys te d 2.5 a 3 r lwa e le c de 5 ...or a past today future st 0.0 0.0 f ir –20 –10 0 10 Billions Years from Today Friday, February 13, 2009
  65. 65. Friday, February 13, 2009
  66. 66. Friday, February 13, 2009
  67. 67. Friday, February 13, 2009
  68. 68. Friday, February 13, 2009
  69. 69. Friday, February 13, 2009
  70. 70. Friday, February 13, 2009
  71. 71. Friday, February 13, 2009
  72. 72. Friday, February 13, 2009
  73. 73. Friday, February 13, 2009
  74. 74. Friday, February 13, 2009
  75. 75. Supernova Cosmology Project 3 Knop et al. (2003) No Big Bang Spergel et al. (2003) Allen et al. (2002) 2 Supernovae 1 ΩΛ CMB expands forever ly ollapses eventual 0 rec Clusters clo se d fla -1 t op en 0 1 2 3 ΩM Friday, February 13, 2009
  76. 76. The fine tuning problem “Natural” value for energy density: or 46,000,000,000,000,000,000,000,000,000,000 ,000,000,000,000,000,000,000,000,000,000,0 00,000,000,000,000,000,000,000,000,000,000 ,000,000,000,000,000 J/m3 Therefore, the cosmological constant was believed to be zero until 1998 Friday, February 13, 2009
  77. 77. No one knows what makes the cosmological constant Is it really constant? Need more distant supernovae Friday, February 13, 2009
  78. 78. Friday, February 13, 2009
  79. 79. Friday, February 13, 2009
  80. 80. SNAP DESTINY ADEPT Friday, February 13, 2009
  81. 81. Supernova Cosmology Project ΩΜ , ΩΛ Knop et al. (2003) 0.25,0.75 0.25, 0 1, 0 24 Supernova 22 Cosmology Project effective mB 20 18 Calan/Tololo & CfA 16 14 0.0 0.2 0.4 0.6 0.8 1.0 redshift z Friday, February 13, 2009
  82. 82. 0.0 Flat Universe network of cosmic strings Constant w –0.2 w = –1/3 –0.4 w = pu / quot;u 99% range of 95% Quintessence –0.6 90% models 68% –0.8 cosmological constant w = –1 –1.0 0.0 0.2 0.4 0.6 0.8 1.0 !M = 1 - !w SNAP Satellite Target Statistical Uncertainty 68%, 90%, 95%, and 99% confidence regions in the ΩM –w plane for an additional energy density component, Ωw , n equation-of-state w = p/ρ. (For Einstein’s cosmological constant, Λ, w = −1.) The fit is constrained to a flat Ωw = 1). Also shown is the expected confidence region allowed by SNAP assuming w = −1 and ΩM = 0.28. wavelength calibrated spectra extending to wavelength regions where “gray” dust is no longer gray will hypothetical large-grain dust’s absorption properties. Armed with the extinction – color excess properties Friday, February 13, 2009
  83. 83. Recap Einstein introduced cosmological constant negative pressure antigravity to allow static universe Cepheid variables used to measure distance (bright, identifiable, known brightness) also used to show expansion of the universe Supernovae much brighter than cepheids, can show expansion in distant galaxies. Expansion of the universe is accelerating, deep challenge to explain why. Friday, February 13, 2009
  84. 84. Recap Einstein introduced cosmological constant negative pressure antigravity to allow static universe Cepheid variables used to measure distance (bright, identifiable, known brightness) also used to show expansion of the universe Supernovae much brighter than cepheids, can show expansion in distant galaxies. Expansion of the universe is accelerating, deep challenge to explain why. Friday, February 13, 2009

×