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Cosmology I & II Expanding universe Hot early universe Nucleosynthesis Baryogenesis Cosmic microwave background (CMB) Structure formation Dark matter, dark energy Cosmic inflation

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UNITS, NOTATION c = ħ= k B = 1 Energy = mass = GeV Time = length = 1/GeV Planck mass M P = 1.22 10 19 GeV Newton’s constant G = 1/ M P 1 eV = 11000 K 1 s ~ 1/MeV 2 Metric signature = (1,-1,-1,-1)

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Quantities, observables Hubble rate = expansion rate of the universe = H Energy density of particle species x = x = E/V Number density n x = N/V Relative He abundance Y = 4 He/(H+ 4 He) Baryon number of the universe (n B -n B )/n Scattering cross section ~ [1/energy 2 ], (decay) rate ~ [energy] ~ n ¯

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(cont) CMB temperature T( ) = T 0 + T( ) (”CMB power spectrum”) Galaxy-galaxy correlators (”Large scale structure” = LSS) Distant supernova luminosities

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The starting point expansion of the universe is very slow (changes adiabatic): H << scattering rates Thermal equilibrium (+ some deviations from: this is where the interesting physics lies) Need: statistical physics, particle physics, some general relativity

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History of cosmology General theory of relativity 1916 –First mathematical theory of the universe –Applied by Einstein in 1917 –Problem: thought that universe = Milky Way → overdense universe → must collapse → to recover static universe must introduce cosmological constant (did not work)

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Theory develops … Willem de Sitter 1917 –Solution to Einstein equations, assuming empty space: (exponential) expansion (but can be expressed in stationary coordinates) Alexander Friedmann 1922 –Solution to Einstein eqs with matter: no static solution –Universe either expanding or collapsing

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Observations Henrietta Leavitt 1912 –Cepheids: luminosity and period related → standard candles Hubble 1920s –1923: Andromeda nebula is a galaxy (Mount Wilson 100” telescope sees cepheids) –1929: redshifts of 24 galaxies with independent distance estimates → the Hubble law v = Hd law v = Hd

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Georges Lemaitre 1927: ”primeaval atom” –Cold beginning, crumbling supernucleus (like radioactivity) George Gamow: 1946-1948 –Hot early universe (nuclear physics ~ the Sun) –Alpher, Gamow, Herman 1948: relic photons with a temperature today of 5 K –Idea was all but forgotten in the 50’s

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Demise of the steady state Fred Hoyle 1950s –”steady state theory”: the universe is infinite and looks the same everywhere –New matter created out of vacuum → expansion (added a source term into Einstein eqs.) Cambridge 3C galaxy survey 1959 –Radiogalaxies do not follow the distribution predicted by steady state theory

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Rediscovery of Big Bang Penzias & Wilson 1965 Bell labs –Testing former Echo 6 meter radioantenna to use it for radioastronomy (1964) –3 K noise that could not be accounted for –Dicke & Peebles in Princeton heard about the result → theoretical explanation: redshifted radiation from the time of matter-radiation decoupling (”recombination”) = CMB –Thermal equilibrium → black body spectrum –Isotropic, homogenous radiation: however, universe has structure → CMB must have spatial temperature variations of order 10 -5 K

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Precision cosmology COBE satellite 1992 –Launch 1989, results in 1992results in 1992 –Scanned the microwave sky with 2 horns and compared the temperature differences –Found temp variations with amplitude 10 -5 K, resolution < 7 OFound Balloon experiments end of 90’sBalloon –Maxima, Boomerang: first acoustic peak discoveredBoomerang LSS surveys –2dF etc 90’s; ongoing: Sloan Digital Sky Survey (SDSS)2dF

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WMAP 2003WMAP –High precision spectrum of temperature fluctuations fluctuations –Determination of all essential cosmological parameters with an accuracy of few %Determination Big bang nucleosynthesis 1980’s → –H, He, Li abundances (N, )abundances Planck Surveyor Mission 2007 (Finland participates)

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Surprises/problems Dark matter (easy) Dark energy (~ cosmological constant, very hard) Cosmic inflation (great, but how?) Baryogenesis (how?- Standard Model not enough)

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