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A description of dark energy.

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- 1. Dark Energy Friday, February 13, 2009
- 2. Friday, February 13, 2009
- 3. Theory Expansion Supernovae Acceleration Friday, February 13, 2009
- 4. Theory Expansion Supernovae Acceleration Friday, February 13, 2009
- 5. Friday, February 13, 2009
- 6. Einstein’s equation says mass/ energy causes space-time curvature • Curvature = Energy Density Friday, February 13, 2009
- 7. What about empty space? Friday, February 13, 2009
- 8. What is so special about empty space? Friday, February 13, 2009
- 9. What is so special about empty space? Can have curvature even with no matter Friday, February 13, 2009
- 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. 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. 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. 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. 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. 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. Recap Einstein introduced cosmological constant negative pressure antigravity to allow static universe Friday, February 13, 2009
- 17. Theory Expansion Supernovae Acceleration Friday, February 13, 2009
- 18. Measure distance in Astronomy by comparing brightness of object to known reference Apparent Magnitude 20 15 Color Friday, February 13, 2009
- 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. Cepheid Variable are a good reference Friday, February 13, 2009
- 21. Henrietta Leavitt discovered Cephied Period Luminosity relation Friday, February 13, 2009
- 22. Original plates used to discover Cepheids Friday, February 13, 2009
- 23. Take negative of one plate Friday, February 13, 2009
- 24. Friday, February 13, 2009
- 25. Overlap eliminates all but variable star Friday, February 13, 2009
- 26. Friday, February 13, 2009
- 27. Friday, February 13, 2009
- 28. Friday, February 13, 2009
- 29. Friday, February 13, 2009
- 30. Friday, February 13, 2009
- 31. Friday, February 13, 2009
- 32. Distance Time Today Friday, February 13, 2009
- 33. Distance Time Today Friday, February 13, 2009
- 34. Distance Time Today Friday, February 13, 2009
- 35. Distance Time Age of the Universe 12 Gya Today Friday, February 13, 2009
- 36. Friday, February 13, 2009
- 37. HST Hubble Constant Key Project Freedman et al. 2001 Friday, February 13, 2009
- 38. Distance Time 12 Gya Today Friday, February 13, 2009
- 39. Distance Time 12 Gya Today Friday, February 13, 2009
- 40. Distance Time Age of the Universe 12 Gya 10 Gya Today Friday, February 13, 2009
- 41. M55 Globular Cluster Friday, February 13, 2009
- 42. Distance Time 12 Gya 10 Gya Today Friday, February 13, 2009
- 43. Formation of Globular Clusters Distance 13 Gya Time Age of the Universe 12 Gya 10 Gya Today Friday, February 13, 2009
- 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. Theory Expansion Supernovae Acceleration Friday, February 13, 2009
- 46. Looking for a brighter standard Cepheids are the brightest stars Supernovae are much brighter than cepheids Friday, February 13, 2009
- 47. A star is in balance between gravity and pressure Hydrostatic equilibrium Friday, February 13, 2009
- 48. When stars are hot, pressure comes from gas pressure PV=NRT Friday, February 13, 2009
- 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. 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. Finite speed of light places a limit on maximum size of core Friday, February 13, 2009
- 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. Two types of supernovas • Binary white dwarf (Type Ia) • Massive star (Type Ib,c Type II) Friday, February 13, 2009
- 54. Friday, February 13, 2009
- 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. Follow up image Friday, February 13, 2009
- 57. Friday, February 13, 2009
- 58. Friday, February 13, 2009
- 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. 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. Theory Expansion Supernovae Acceleration Friday, February 13, 2009
- 62. Distance Time 12 Gya 10 Gya Today Friday, February 13, 2009
- 63. Formation of Globular Clusters Distance 13 Gya Time Age of the Universe 12 Gya 10 Gya Today Friday, February 13, 2009
- 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. Friday, February 13, 2009
- 66. Friday, February 13, 2009
- 67. Friday, February 13, 2009
- 68. Friday, February 13, 2009
- 69. Friday, February 13, 2009
- 70. Friday, February 13, 2009
- 71. Friday, February 13, 2009
- 72. Friday, February 13, 2009
- 73. Friday, February 13, 2009
- 74. Friday, February 13, 2009
- 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. 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. No one knows what makes the cosmological constant Is it really constant? Need more distant supernovae Friday, February 13, 2009
- 78. Friday, February 13, 2009
- 79. Friday, February 13, 2009
- 80. SNAP DESTINY ADEPT Friday, February 13, 2009
- 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. 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. 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. 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

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