29_-_Cosmology_2 - 29 - Cosmology(2) The General Idea As we...

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2 The General Idea • As we go back in time the Universe gets more and more congested – The galaxies are close together – The Background photons are more energetic • As the Universe becomes hotter its constituents change. Eventually there will only be photons. • Who knows what’s before that? 3 Radiation Only Universe • In the early times the Universe was filled with radiation; there was no matter. • The blackbody radiation was characterized by the Stefan-Boltzmann equation: F = σ T 4 (w/m 2 ) The energy density of the radiation was: F/c = σ T 4 /c The corresponding mass density was: ρ = σ T 4 /c 3 (g/m 3 ) 4 Radiation Dominated with k=0 2 0 4 2 0 4 1 2 0 2 8 ( ) 3 8 3 8 3 R G t R R R G R R R G R π ρ = = = = Friedmann equ. for k=0 The effective mass of the BB radiation: Flux = σ T 4 Equivalent mass flux = Flux/c 2 ρ α ρ o /R 4
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29_-_Cosmology_2 - 29 - Cosmology(2) The General Idea As we...

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