Lecture 29: Cosmology Hubble compared the distances he measured for galaxies with their Doppler shift of spectral lines. Further = higher velocity away Galaxies are red shifted V = H0 d -> hubbles law H0 = 70 km/sec/Mpc Mpc= megaparsec Redshift Z = (L ?L0)/L0 where L0 = rest wavelength At low velocity z ~ v/c Cosmology is the study of the structure and evolution of the universe. On every scale observed so far the universe shows structure: stars form star clusters and galaxies galaxies form galaxy clusters and superclusters, and other large structures Big Structures 200 MPC have been seen Some distant stuff are 4000 MPC 300 Mpc cube ~ 100000 galaxies Universe has about 125-150 galaxies Two assumptions: Universe is smooth The same in every direction Universe has no center Olbers?s Paradox ? If universe is infinite with uniform density, the sky should be bright Universe is not infinite because it has finite age Universe changes with time According to Hubble?s law, at one point galaxies were on top of each other. T = d/v = 1/H0 If H0 = 100 km/sec/Mpc Then t = 10^10 years The Big Bang Big Bang was not explosion in an empty universe Big Bang is the entire universe exploding Everything happened at the same time If we look back we see back in time
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