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Cosmology Lecture 4 Constituents Protons Neutrons Electrons mass (Mev) 983.3 939.6 0.511 charge +1 0 -1 Photons Neutrinos 0 ? 0 0 Dark matter ? 0 Dark Energy ? 0 Overall, the universe is flat Ω 4% 23% 73% Cosmological constant Contributes most of the energy of the universe? What is the evidence for this? What impact does it have on universal evolution? Standard Candles Known luminosity => brightness gives distance “Standardized candles” - not quite “standard”, but various relationships can give true luminosity Cepheids - Period-Luminosity relation (visible to z=0.01) SN Ia - Peak magnitude - decay rate relation (visible to z=1.5) Type Ia Supernovae The Philips relation σ ~ 0.3 mag σ ~ 0.07 mag SN Ia Hubble Diagram SN Ia at higher redshift are too faint Further away than we expect Universe is accelerating - first evidence for cosmological constant This is a BIG suprise Scale factor k<0 Λ k=0 k>0 Time Back to the Friedman equation Useful, but contains too many unknowns Need some more equations to solve for a(t), ε, k, Λ etc The fluid equation Comes from first law of thermodynamics (essentially conservation of energy) Links energy density and pressue The acceleration equation Combination of Fluid and Friedman Equations Not independent - unfortunately, we still need more! And finally……equations of state Equation of state links P and ε Define equation of state parameter ω P=ωε ω = 0 - matter dominated universe ω = 1/3 - radiation dominated universe ω = -1 - cosmological constant dominated universe Cosmological Models We are now (finally) in a position to describe the evolution of a universe consisting of Matter Radiation Cosmological Constant Provides quantative predictions Next lecture