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lecture17 - Cosmology structure and evolution of the...

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Cosmology : structure and evolution of the universe Questions and issues: size of universe -- infinite or finite age -- limited or forever (in future and in past) structure -- hierarchies : large scale struct. / galaxies / stars evolution -- relative amounts of matter and radiation atomic composition due to finite speed of light ==> can effectively look back in time
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Olbers paradox (dark night sky) => finite spatial / temporal duration Hubble recession of galaxies => universe expansion Big Bang Nuceosynthesis Cosmic microwave background (CMB) => radio emission filling all of univ. radiation of the Big Bang Major observations : 2.725 K blackbody spectrum
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expansion of scale of universe Hubble law : V = H 0 R overall scale of universe increasing distance bet. Gal. λ of photons => redshift every point sees galaxies moving away in all directions ==> can’t tell center space through which EM wave travels is expanding ==> stretches wavelength
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Big Bang Nucleosynthesis (Gamow & Alpher ‘48) : at ~10-100 sec, as universe cools (10 9 10 6 K), slight excess of p’s over n’s (n has higher mass & decays τ ~ 15 min) p+n ==> d d ==> destroyed at high T d + p ==> 3 He + n ==> 4 He + p ==> 5 Li * + n =?=> 6 Li ( * -- unstable) universe expands rapidly enough that not all H goes to He amount of He/H set by rate of expansion amt. of d now : a sensitive indicator of total matter density (if enough matter to close univ. , d + d ==> He more efficient
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