The History and Philosophyof Astronomy (Lecture 20: Perspective:The Victorian Universe)Instructor: Volker BrommTA: Amanda BauerThe University of Texas at AustinAstronomy 350L (Spring 2005)General Timeline timeEnlightenment(1750-1830)Victorian Age(1830-1901)Expressionism(early 20thcent.)General Timeline timeEarly 20thcent.Enlightenment(1750-1830)Victorian Age(1830-1901)EinsteinEarl of RosseWilliam HerschelThe Victorian Age (1830-1901) • Age of Contradictions!• destitute poverty• industrial vigorThe Victorian Age (1830-1901) • Reign of Queen Victoria(1837-1901)• Epoch of Imperialism• Vigorous economicexpansion, based onindustrialized productionThe Victorian Age (1830-1901) • The Great Exhibition 1851• London, Crystal PalaceVictorian Age: Thermodynamics • Conservation of energy! • Increasing entropy: From order to chaos!Great Achievement: Stellar Parallax! • Bessell 1838: 61 Cygni, d = 10.3 lightyearsGreat Achievement: Stellar Spectra • The Laws of Spectroscopy (Kirchhoff/Bunsen):- dark lines = absorption lines- bright lines = emission linesGreat Achievement: Discovery of Neptune 1846 • Existence of new planet predicted and discovered!(Voyager 1989)Baroque Astronomy in Perspective (1750) • Status of knowledge on:- concept of space- concept of time- nature of stars - concept of motion  modern (Newton) - Architecture of Solar System  modern (Newton)Victorian Astronomy in Perspective (1900) • Status of knowledge on:- spatial structure of universe - architecture of stellar system (Milky Way)- age of the universe- stellar distances  modern (several lightyears) - nature of stars  towards modern view19thCentury: Spatial Structure of Universe • infinite, 3-dimensionalEuclidean space• Cartesian coordinates(x,y,z)• Q: Is space full (no vacuum), or (partially) empty?19thCentury: Spatial Structure of Universe • Q: Is space full (no vacuum), or (partially) empty?• all of space pervaded by invisible ether!Architecture of Stellar System William Parsons,3rdEarl of Rosse(1800-67)“Leviathan of Parsonstown”Architecture of Stellar System • His sketch of M51 (1845): First Spiral Nebula• Speculate: -- Galaxy in rotation? -- A galaxy (system of stars), or gaseousnebula?Architecture of Stellar System One-island universe• Two basic models:Many-island universe (Kant)Architecture of Stellar System • Jacobus Kapteyn (1851-1922)• Professor at Groningen University (The Netherlands)• Census of the sky• `The Kapteyn Universe’(Universe = Milky Way)Architecture of Stellar System • one-island universe (Milky Way = Universe)• Solar System close to the center• surrounded by infinite (starless) voidArchitecture of Stellar System • 19thcentury astronomers only saw nearby stars,because of interstellar extinction (dust)!Interstellar Dust • Interstellar dust only discovered in 20thcentury!The Stoic UniverseInfinite voidFinite cosmosFixed starsEarth???Three World Systems: Plenum vs VacuumAristotelianStoicEpicurean• space:• matter:-finite -infinite -infinite-finite -finite -infiniteProblem with Victorian universe: Gravitational Instability! • Ad hoc fix: Have to assume that gravity does notobey inverse-square law at large distances!19thCentury View: Age of the Universe • Solar System (and the stars) have a finite age(millions to billions of years)• But what about the universe as a whole?• Recall view at end of Baroque Period (~1750)!Baroque: Creation of Universe • before creation: empty space and time, no matter!Baroque: Creation of Universe • after creation: empty space and time with matter everywhere!19thCentury View: An Eternal Universe • space, time, and (finite) matter have existed forever!19thCentury View: An Eternal Universe • (finite) matter was more diffuse in the past!19thCentury View: Age of the Universe • Solar System (and the stars) have a finite age(millions to billions of years)• But what about the universe as a whole?• A: Universe as a whole is eternal!• Put differently: The contents of the universe isconstantly changing (evolving), but the universeas a whole is not!• Conceptually, this is not convincing!Great Task Ahead: Origin of Universe and Time! • The Big Bang!Olbers’Paradox: Darkness at Night • Olbers asks (1823):“In an infinite and eternal universe:Why is the sky dark at night?”• Wilhelm Olbers(1758-1840)• German physician andamateur astronomerVictorian Universe: Resolve Olbers’Paradox • In universe with infinity of stars: No darkness at night!Victorian Universe: Resolve Olbers’Paradox • In universe with infinity of stars: No darkness at night!Victorian Universe: Resolve Olbers’Paradox • In universe with finite # of stars: Darkness at night!Perspective: The Victorian Universe• Successfully explained: - Sun and stars are made of normal matter- spectra of Sun and stars- distance scale of the stars• New questions/problems: - How is an eternal universe consistent with finite Sun?- What is the true nature of the Spiral Nebulae (e.g., M51)?- What is true architecture of Milky Way?- Why does Milky Way not collapse to a point?- Physical nature of the stars (and