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Cosmology : a short introduction

Cosmology : a short introduction. Mathieu Langer Institut d’Astrophysique Spatiale Université Paris-Sud XI Orsay, France. Egyptian School on High Energy Physics CTP-BUE , Egypt 27 May – 4 June 2009. 0. What do we see ?. (depends on wavelength…).

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Cosmology : a short introduction

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  1. Cosmology : a short introduction Mathieu Langer Institut d’Astrophysique Spatiale Université Paris-Sud XI Orsay, France Egyptian School on High Energy Physics CTP-BUE , Egypt 27 May – 4 June 2009

  2. 0. What do we see ? (depends on wavelength…)

  3. Cosmic Microwave Background (detected 1965, Penzias & Wilson, Nobel prize 1978) (COBE data, 1996)

  4. First detection 1965 at 7.35 cm Penzias & Wilson Nobel Prize 1978

  5. What Penzias & Wilson would have seen, had they observed the full sky The Milky Way Cosmological interpretation: Dicke, Peebles, Roll, Wilkinson (1965)

  6. Cosmic Microwave Background (detected 1965, Penzias & Wilson, Nobel prize 1978) (COBE data, 1996)

  7. The Cosmic Microwave Background : a “perfect” black body

  8. The Cosmic Microwave Background : a “perfect” black body

  9. CMB : tiny anisotropies COBE, 1991-1996 First detection of anisotropies (Nobel prize 2006: Smoot & Mather)

  10. CMB : tiny anisotropies, huge information -200 µK < ΔT < 200 µK First fine-resolution full-sky map (0.2 degrees) WMAP: 2003, 2006, 2008 (Launched June 2001)

  11. CMB anisotropies : angular power spectrum From temperature maps… …to power spectra…

  12. …to cosmological parameters and cosmic pies : Age : 13.7 billion years

  13. Panoramic view of the entire near-infrared sky Blue : nearest galaxies Red : most distant (up to ~ 410 Mpc) Distribution of structure on large scales (2MASS, XSC & PSC)

  14. Notice : isotropy & homogeneity!

  15. Hubble’s law, expansion of the universe V = H0 D H0 = 71 ± 4 km/s/Mpc (from WMAP + Structures) (Hubble, 1929) Rem : 1 parsec ~ 3.262 light years ~ 3.1×1013 km

  16. Ambitious cosmology…

  17. Our understanding of the universe…

  18. 1. How do we understand what we see?

  19. Cosmological principle Universe : spatially homogeneous & isotropiceverywhere  Applies to regions unreachable by observation Copernican principle Our place is not special  observations are the same for any observer Isotropy + Copernicus  homogeneity  Applies to observable universe Fundamental principles

  20. Friedmann-Lemaître-Robertson-Walker metric Maximally symmetric space-time equivalent to where

  21. Coordinates : Scale factor a(t): Redshift & Expansion : Scale factor, expansion, Hubble’s law

  22. Hubble’s flow : 2 observers at comoving coordinates x1 & x2 Physical distance : Separation velocity : Proper velocities Galaxy moving relative to space fabric  x not constant Velocity : Scale factor, expansion, Hubble’s law  scatter in Hubble’s law for nearby galaxies

  23. Einstein equations : geometry  energy content Friedmann equations : dynamics of the Universe Dynamics : Einstein, Friedmann, etc. Stress-energy tensor: Expansion rate Variation of H

  24. Critical density : put k = 0 today (cf. measurements!) Density parameters : Equation of state : for each fluid i : pi = wiρi Dynamics and cosmological parameters and today: • Photons : p = ρ/3  wr=1/3 • Matter : ρ = mn, p = nkTρ wm = 0

  25. Friedmann equations expansion variation acceleration Matter-Energy conservation : Dynamics of the Universe so clearly (Rem: only 2 independent equations)

  26. Evolution of a given fluid : Conservation equation gives Summary : * assume wi constant, * integrate Rem : C.C.  wΛ= -1

  27. Matter-radiation equality Expansion history wrt. dominant fluid Universe Expansion History (from WMAP)  for zzeq : Universe dominated by radiation 

  28. Acceleration wrt. fluid equation of state of dominant fluid Deceleration Acceleration Universe Expansion History Matter and radiation OK Observed accelerationrequires exotic fluid withnegative pressure!

  29. Back to the CMB… time, age density, z, T radiation & matter in thermal equilibrium radiation & matter live separate lives

  30. CMB : Primordial Photons’ Last Scattering 380 000 years time, age (Planck) density, z, T radiation & matter in equilibrium via tight coupling radiation & matter are decoupled, no interaction CMB z =1100

  31. The CMB : a snapshot of the Baby Universe

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