Lecture20 - Signature Course UGS 303 (Fall 2009) What is...

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1 The History and Philosophy of Astronomy (Lecture 20: Steady State vs. Big Bang) Instructor: Volker Bromm The University of Texas at Austin Department of Astronomy Signature Course UGS 303 (Fall 2009) (Substitute for today ʼ s lecture: Eiichiro Komatsu) What is Steady State Universe? What is Big Bang Universe? Steady State Big Bang Does the Universe Expand? Was the Universe Hot in the Past? Does the Universe Have a Beginning? Does the Universe Have an End The Universe Is Expanding Edwin Hubble (1929) Big Bang Model Steady State Model George Lemaitre (1931) George Gamow (1948) Herman Bondi, Fred Hoyle (1948)
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2 Origin of the Big Bang Model • 1922: A theoretical proposal of an expanding universe. • He solved " Einstein ʼ s " equations of General Relativity. Alexander Friedmann (1888-1925) Separation Between Galaxies Time Origin of the Big Bang Model • 1927: Lemaitre independently found the expanding-universe solutions of Gen. Relativity Abbe Georges Lemaitre (1894-1966) Lemaitre meets Einstein (Pasadena, 1933) Origin of the Big Bang Model • Lemaitre: Imagine that you run expansion of universe backwards in time! Cosmic time observer • in distant past: universe was much denser and hotter! Origin of the Big Bang Model • 1931: Lemaitre ʼ s “Primeval Atom”: • The entire universe was packed into a single atom (But, we do not adopt this view now) • He clearly stated the existence of the beginning of space and time Lemaitre: “Father of the Big Bang”
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3 The Steady State Model (1948) • worked out at Cambridge University, England Hermann Bondi (1919-2005) Thomas Gold (1920-2004) Fred Hoyle (1915-2001) Steady State Model Steady state universe Evolving universe (“Big Bang”) • density changes with time • past different from present • beginning of time (“Big Bang”) • density constant over time • the universe appears to be the same at all times • no beginning of time Steady State Model Steady state universe Evolving universe (“Big Bang”)
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Lecture20 - Signature Course UGS 303 (Fall 2009) What is...

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