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Dunkle Energie – Ein kosmisches Raetsel

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  1. Dark Energy- a cosmic mystery Dunkle Energie – Ein kosmisches Raetsel

  2. Quintessence C.Wetterich A.Hebecker,M.Doran,M.Lilley,J.Schwindt, C.Müller,G.Schäfer,E.Thommes, R.Caldwell,M.Bartelmann

  3. What is our universe made of ? fire , air, water, soil ! quintessence !

  4. Dark Energy dominates the Universe Energy - density in the Universe = Matter + Dark Energy 30 % + 70 %

  5. What is Dark Energy ?

  6. Matter : Everything that clumps Abell 2255 Cluster ~300 Mpc

  7. critical density • ρc =3 H² M² critical energy density of the universe ( M : reduced Planck-mass , H : Hubble parameter ) • Ωb=ρb/ρc fraction in baryons energy density in baryons over critical energy density

  8. Dark Matter Most matter is dark ! So far tested only through gravity Every local mass concentration gravitational potential Orbits and velocities of stars and galaxies measurement of gravitational potential and therefore of local matter distribution

  9. Ωm= 0.3 gravitational lens , HST

  10. spatially flat universe Ωtot = 1 • theory (inflationary universe ) Ωtot =1.0000……….x • observation ( WMAP ) Ωtot =1.02 (0.02)

  11. picture of the big bang

  12. Ωtot=1

  13. Dark Energy Ωm + X = 1 Ωm : 30% Ωh : 70% Dark Energy h : homogenous , often ΩΛ instead of Ωh

  14. Space between clumps is not empty :Dark Energy !

  15. Dark Energy density isthe same at every point of space “ homogeneous “ No force –“ In what direction should it draw ? “

  16. Two important predictions The expansion of the Universe accelerates today ! Structure formation : One primordial fluctuation- spectrum

  17. consistent cosmological model !

  18. Composition of the Universe Ωb = 0.045 visible clumping Ωdm= 0.22 invisibleclumping Ωh = 0.73 invisiblehomogeneous

  19. Dark Energy- a cosmic mystery Dunkle Energie – Ein kosmisches Raetsel

  20. What is Dark Energy ? Cosmological Constant or Quintessence ?

  21. Cosmological Constant- Einstein - • Constant λ compatible with all symmetries • No time variation in contribution to energy density • Why so small ? λ/M4 = 10-120 • Why important just today ?

  22. Cosm. Const. | Quintessence static | dynamical

  23. Energy density ρ ~ ( 2.4×10 -3 eV )- 4 Reduced Planck mass M=2.44×1018GeV Newton’s constant GN=(8πM²) Cosmological mass scales Only ratios of mass scales are observable ! homogeneous dark energy: ρh/M4 = 6.5 10ˉ¹²¹ matter: ρm/M4= 3.5 10ˉ¹²¹

  24. Time evolution tˉ² matter dominated universe tˉ3/2 radiation dominated universe • ρm/M4 ~ aˉ³ ~ • ρr/M4 ~ aˉ4~ t -2radiation dominated universe Huge age small ratio Same explanation for small dark energy?

  25. Quintessence Dynamical dark energy , generated by scalar field (cosmon) C.Wetterich,Nucl.Phys.B302(1988)668, 24.9.87 P.J.E.Peebles,B.Ratra,ApJ.Lett.325(1988)L17, 20.10.87

  26. Prediction : homogeneous dark energyinfluences recent cosmology- of same order as dark matter - Original models do not fit the present observations …. modifications

  27. Quintessence Cosmon – Field φ(x,y,z,t) similar to electric field , but no direction ( scalar field ) Homogeneous und isotropic Universe : φ(x,y,z,t)=φ(t) Potential und kinetic energy of the cosmon -field contribute to a dynamical energy density of the Universe !

  28. “Fundamental” Interactions Strong, electromagnetic, weak interactions On astronomical length scales: graviton + cosmon gravitation cosmodynamics

  29. Evolution of cosmon field Field equations Potential V(φ) determines details of the model e.g. V(φ) =M4 exp( - φ/M ) for increasing φ the potential decreases towards zero !

  30. Cosmological equations cosmon +matter example:

  31. Cosmon • Scalar field changes its value even in the presentcosmological epoch • Potential und kinetic energy of cosmon contribute to the energy density of the Universe • Time - variable dark energy : ρh(t) decreases with time !

  32. Cosmon • Tiny mass • mc ~ H • New long - range interaction

  33. Dynamics of quintessence • Cosmonj: scalar singlet field • Lagrange density L = V + ½ k(φ)¶j ¶j (units: reduced Planck mass M=1) • Potential : V=exp[-j] • “Natural initial value” in Planck era j=0 • today: j=276

  34. cosmon mass changes with time ! for standard kinetic term • mc2 = V” for standard exponential potential , k = const. • mc2 = V”/ k2 = V/( k2 M2 ) = 3 Ωh (1 - wh ) H2 /( 2 k2 )

  35. Cosmological equations

  36. Cosmic Attractors Solutions independent of initial conditions typically V~t -2 φ ~ ln ( t ) Ωh ~ const. details depend on V(φ) or kinetic term early cosmology

  37. Quintessence becomes important “today”

  38. Equation of state p=T-V pressure kinetic energy ρ=T+V energy density Equation of state Depends on specific evolution of the scalar field

  39. Negative pressure • w < 0 Ωh increases (with decreasing z ) • w < -1/3 expansion of the Universe is accelerating • w = -1 cosmological constant late universe with small radiation component :

  40. small early and large presentdark energy fraction in dark energy has substantially increased since end of structure formation expansion of universe accelerates in present epoch

  41. Quintessence becomes important “today” No reason why w should be constant in time !

  42. How can quintessence be distinguished from a cosmological constant ?

  43. Time dependence of dark energy cosmological constant : Ωh ~ t² ~ (1+z)-3 M.Doran,…

  44. Measure Ωh(z) !

  45. Early dark energy A few percent in the early Universe Not possible for a cosmological constant

  46. Early quintessence slows down the growth of structure

  47. A few percent Early Dark Energy If linear power spectrum fixed today ( σ8 ) : More Structure at high z ! Bartelmann,Doran,…

  48. How to distinguish Q from Λ ? A) Measurement Ωh(z) H(z) i) Ωh(z) at the time of structure formation , CMB - emission or nucleosynthesis ii) equation of state wh(today) > -1 B) Time variation of fundamental “constants” C) Apparent violation of equivalence principle

  49. Quintessence and time variation of fundamental constants Generic prediction Strengthunknown Strong, electromagnetic, weak interactions C.Wetterich , Nucl.Phys.B302,645(1988) gravitation cosmodynamics