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Cosmology : Cosmic Microwave Background & Large scale structure & Large scale structure Cosmology : Cosmic Microwave Background & Large scale structure & Large scale structure Tarun Souradeep I.U.C.A.A. Cosmology IUCAA VSP program (May 18-22, 2012) Lec. 1: Background universe
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Andromeda Galaxy The Realm of Cosmology Basic unit: Galaxy Size : 10-100 kilo parsec (kpc.) Mass : 100 billion Stars Measure distances in light travel time 1 pc. (parsec) = 200,000 AU = 3.26 light yr. Measure Mass in Solar mass
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The Realm of Cosmology 100 million Light years
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The Realm of Cosmology 500 million Light years
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The Realm of Cosmology 5 Billion Light years
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The Realm of Cosmology
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How can we even hope to comprehend this immensely large& complex Universe !?! Look for an appropriate simple model
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Modeling nature Picasso: Steiren series
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Lick Observatory survey North South The Isotropic Universe Distribution of galaxies on the sky is broadly isotropic Isotropy around every point implies Homogeneity Cosmological principle FLRW models
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The Expanding Universe Leads to the Hubble’s law Recession velocity is Proportional to the distance Matter density: 1/V Radiation density: 1/(V L) Early Universe is radiation dominated E Einstein’s General relativity applied to an uniform distribution of matter on cosmic scales leads to a smooth expanding universe (FRW Cosmology) Fig.: Ned Wright
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The Expanding Universe Fig.: Ned Wright
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Space-time of the cosmos Fig.: Ned Wright
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Space-time of the cosmos General relativity allows us to formulate physics in any coordinates Fig.: Ned Wright
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Space-time of the cosmos Fig.: Ned Wright Comoving spatial coordinates
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Space-time of the cosmos Fig.: Ned Wright Comoving spatial coordinates Conformal time
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Observer Distant galaxy Equal time events at a distant galaxy appears time-dilated Cosmological Redshift Frequency of light from a distant galaxy is scaled by the expansion Redshift, z=v/c Redshift is related to distance Fig.: adapted from Ned Wright
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Expanding Universe Hubble’s measurements in 1929 Hubble’s law: Recession velocity of galaxies is proportional to the distance Fig.: Ned Wright Frequency of light from a distant galaxy Redshift, z=v/c Redshift is related to distance
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Expanding Universe Hubble’s Law: Current observational status Fig.: Ned Wright
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Post-recombination :Freely propagating through (weakly perturbed) homogeneous & isotropic cosmos. Pre-recombination : Tightly coupled to, and in thermal equilibrium with, ionized matter. Pristine relic of a hot, dense & smooth early universe - Hot Big Bang model (text background: W. Hu) Cosmic Microwave Background
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Cosmic “Super–IMAX” theater Transparent universe Opaque universe 43 Billion Light-years Here & Now (14 Giga-years) 0.5 Mega-years
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The Isotropic Universe T 0 =2.725 (+/-0.002)K. Serendipitous discovery of the dominant Radiation content of the universe as an extremely isotropic, Black-body bath at temperature T 0 =2.725 (+/-0.002)K. “Clinching support for Hot Big Bang model” Nobel prize 1978 Cosmic Microwave Background
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The dominant radiation component in the universe (D. Scott ’99) ~ 400 CMB photons per cubic cm. Cosmic Microwave Background
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“Dust” in an expanding box Radiation in an expanding box Size = ½ Number density x 8 Energy density x 16 Temperature x 2 Size = ¼ Number density x 64 Energy density x 128 Temperature x 4 Size = ¼ Number density x 64 Energy density x 64 Size = ½ Number density x 8 Energy density x 8 time Matter density: 1/V Radiation density: 1/(V L) Early Universe is radiation dominated E
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The most perfect Black-Body spectrum in nature COBE website COBE –FIRAS The CMB temperature – A single number characterizes the radiation content of the universe!! Cosmic Microwave Background
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Baryons: Big Bang Nucleosynthesis
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Flat Universe Hyperbolic Universe Constant negative curvature Spherical Universe Constant positive curvature Geometry of the Universe
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Friedman equations
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Evolution of density
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`Standard’ cosmological model: Geometry, Expansion & Matter Clustering matter Non-Clustering matter
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How much do we now know about this model Universe ? lots !!!
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NASA/WMAP science team Age of the universe Dark energy density Dark matter density Expansion rate of the universe Good old Cosmology, … New trend ! Total energy density Baryonic matter density
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