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

Quantities, observables Hubble rate = expansion rate of the universe = H Energy density of particle species x:  x = E x /V Number density n x = N x /V Relative energy density  x =  x /  c 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 ¯ critical

(cont) CMB temperature T(x,y) = T 0 +  T(x,y) CMB power spectrum P(  )~ Galaxy-galaxy correlators (”Large scale structure” = LSS) Distant SNIa supernova luminosities

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

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)

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

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

Georges Lemaitre 1927: ”primeaval atom” –Cold beginning, crumbling supernucleus (like radioactivity) George Gamow: –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

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

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 K

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 K, resolution < 7 O Balloon experiments end of 90’s –Maxima, Boomerang: first acoustic peak discoveredBoomerang LSS surveys –2dF etc 90’s; ongoing: Sloan Digital Sky Survey (SDSS)2dF

WMAP 2003 –High precision spectrum of temperature fluctuations fluctuations –Determination of all essential cosmological parameters with an accuracy of few % Big bang nucleosynthesis 1980’s → –H, He, Li abundances (N,  )abundances Planck Surveyor Mission 2008 (Finland participates)

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

timeline Temperature ~ Thermal equilibrium, radiation dominated universe: T 2 t ~ 0.3/g 1/2 degrees of freedom

Period of superluminal expansion (cosmic inflation) Cold universe E=10 19 GeV Transition from quantum to classical String theory?GR: time coordinate begins E=10 12 GeV release of the energy driving inflation (reheating) beginning of hot big bang and normal adiabatic Hubble expansion RT=const. thermalization; energy dominated by radiation = UR particles T = 1 TeV sphaleron transitions wash away primordial baryon asymmetry Supersymmetric Standard Model?

Electroweak phase transition Higgs field condenses particles become massive free quarks, antiquarks and gluons T = 200 GeV T = 5 GeV T = 200 MeV baryon-antibaryon annihilation QCD phase transition T = 80 GeV Z,W annihilate p,n,p,n,  + unstable baryons _ c-quarks annihilate T = 1.5 GeV b-quarks annihilate n q = n e = n = 3n  /4 all Standard Model dofs present in plasma baryogenesis? generation of relic cold dark matter? t-quarks annihilate

neutrino freeze-out p and n fall out of equilibrium free neutron decay begins photodissociation of 3 H end of free n decaysynthesis of 4 He begins synthesis of light elements almost complete n p =n n << n  T = 2 MeV T = 0.7 MeV T = 0.1 MeV t = 180 s t = 3.8 × 10 5 yrs matter-radiation equality Dark energy starts to dominate photon-baryon decoupling  CMB T = 0.5 MeV e + e - annihilation kinetic equilibrium by virtue of np↔e +, pe - ↔n etc. structure formation