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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 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…)
Cosmic Microwave Background (detected 1965, Penzias & Wilson, Nobel prize 1978) (COBE data, 1996)
First detection 1965 at 7.35 cm Penzias & Wilson Nobel Prize 1978
What Penzias & Wilson would have seen, had they observed the full sky The Milky Way Cosmological interpretation: Dicke, Peebles, Roll, Wilkinson (1965)
Cosmic Microwave Background (detected 1965, Penzias & Wilson, Nobel prize 1978) (COBE data, 1996)
CMB : tiny anisotropies COBE, 1991-1996 First detection of anisotropies (Nobel prize 2006: Smoot & Mather)
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)
CMB anisotropies : angular power spectrum From temperature maps… …to power spectra…
…to cosmological parameters and cosmic pies : Age : 13.7 billion years
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)
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
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
Friedmann-Lemaître-Robertson-Walker metric Maximally symmetric space-time equivalent to where
Coordinates : Scale factor a(t): Redshift & Expansion : Scale factor, expansion, Hubble’s law
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
Einstein equations : geometry energy content Friedmann equations : dynamics of the Universe Dynamics : Einstein, Friedmann, etc. Stress-energy tensor: Expansion rate Variation of H
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 = nkTρ wm = 0
Friedmann equations expansion variation acceleration Matter-Energy conservation : Dynamics of the Universe so clearly (Rem: only 2 independent equations)
Evolution of a given fluid : Conservation equation gives Summary : * assume wi constant, * integrate Rem : C.C. wΛ= -1
Matter-radiation equality Expansion history wrt. dominant fluid Universe Expansion History (from WMAP) for zzeq : Universe dominated by radiation
Acceleration wrt. fluid equation of state of dominant fluid Deceleration Acceleration Universe Expansion History Matter and radiation OK Observed accelerationrequires exotic fluid withnegative pressure!
Back to the CMB… time, age density, z, T radiation & matter in thermal equilibrium radiation & matter live separate lives
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