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UT AST 350L - Lecture 21- Einstein I

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The History and Philosophyof Astronomy (Lecture 21: Einstein I)Instructor: Volker BrommTA: Amanda BauerThe University of Texas at AustinAstronomy 350L (Spring 2005)Albert Einstein: Revolutionary of Physics • 1879 (Ulm) – 1955 (Princeton)• revolutionized concepts ofspace, time, and gravity- Special Relativity (1905): E=mc2- General Relativity (1915): new theory of gravity• co-founder of quantum theory photonsAlbert Einstein: Person of the Century • pre-eminent scientist of 20th century • acquired world-wide fame after 1919 (eclipse experimentproves his theory of gravity correct)• influence in politics- urges FDR to build atomic bomb- leading supporter of pacifismOverview: Einstein’s Life April 7April 12Birth in Ulm (1879)Youth in Munich (1880-1894) • cozy, middle-class childhood in Bavaria’s capitalYouth in Munich (1880-1894) • traumatic experience in authoritarian school system!Early Life in Switzerland (1895-1914)Prep-school in Aarau (1895-1896) • Einstein enjoys more liberal Swiss school system!Prep-school in Aarau (1895-1896) • a good school leaving certificate!University Student in Zurich (1896-1900) • studies at Swiss Federal Institute of Technology (ETH)• his professors don’t like him  he is too independentPatent Office Clerk in Bern (1902-1909) • Expert 3rdclass• 1905: Annus Mirabilis- Special Relativity- Photons- Reality of atoms• Marriage and children1stMarriage and Children • marriage with Mileva Maric (1903-1919)1905: AnnusMirabilis • Quantum Theory: particles of light (photons)• Special Relativity: new concept of space and time• Brownian motion: prove reality of atomsAnnusMirabilis I: Light quanta • photoelectric effectAnnusMirabilis I: Light quanta • Frequency counts, not intensity!AnnusMirabilis I: Light quanta • Einstein’s idea: light can beboth particle and wave! Low energy! High energy!energyAnnusMirabilis I: Light quanta • Einstein’s explanation: Need sufficiently energeticlight particle (photon)  ultraviolet!The Meaning of Quantum Theory • Quantum theory is weird!The Meaning of Quantum Theory Bohr: we can only knowprobabilities (Copenhagen Interpretation)Einstein: rejects probability interpretation(“God does not play dice!”);postulates `hidden parameters’AnnusMirabilis I: Light quanta • 1921: Nobel Prize in PhysicsAnnusMirabilis II: Special Relativity • Big question for 19thcentury: What is the ether?Light waveether• known: speed of light (c) with respect to ether- c = 300,000 km s-1AnnusMirabilis II: Special Relativity • Big question for 19thcentury: What is the ether?• Michelson’s idea: detect effect of “ether wind”Albert Michelson (1852-1931)- America’s 1stNobel Laureate in physics (1907)AnnusMirabilis II: Special Relativity • 1887: Michelson-Morley experiment• `Michelson interferometer’: measures tiny differences in light-travel timeAnnusMirabilis II: Special Relativity • 1887: Michelson-Morley experiment• Shocking result: No detectabledifference in light-travel timefor perpendicular directions! no difference in speedof light! the ether does not exist!!! • most famous “null result”in history!AnnusMirabilis II: Special Relativity • Big Q: Relative to what do we measure speedof light if there is no light-carrying ether???• Einstein’s idea: Relative to the observer!- And: All observers are equal, as long asthey move with constant speed !(Principle of Relativity)- And: All observers measure same speed of light!AnnusMirabilis II: Special Relativity • Principle of Relativity (first proposed by Galileo)• All observers (moving at constant speed) experience same physics!AnnusMirabilis II: Special Relativity • fundamental change in our understanding ofspace and time: Time DilationLight clock• astronaut: 1 sec• observer on Earth: 10 secAnnusMirabilis II: Special Relativity • Consequence of time dilation: Twin Paradox• fast-moving twin ages less!AnnusMirabilis II: Special Relativity • fundamental change in our understanding ofspace and time: Length ContractionAnnusMirabilis II: Special Relativity • space and time can be transformed into each other! concept of spacetime!Hermann MinkowskiAnnusMirabilis II: Special Relativity • equivalence of mass and energy:Energy Source of the Stars: • nuclear fusion:4 protons (H)  1 helium (He) nucleus• He nucleus has a bitless mass than sum of4 protons (mass defect)• missing mass = energy(Einstein’s E=m c2)Astrophysics and the Bomb• Hiroshima bomb: 1 gram of uraniumEinstein’s Genius Recognized• Max Planck becomes ardentsupporter of Einstein early on!Einstein’s Genius Recognized• 1914: Max Planck secures Einstein’s appointmentas professor in BerlinEinstein (part 1)• Early Life:- 1879: Born in Ulm, Germany- School (Gymnasium) in Munich- since 1895 in Switzerland- 1896-1900: Attends ETH- 1902-09: Patent clerk in Bern- 1903: marries Mileva Maric• Annus Mirabilis (1905):- Special Relativity- Quantum theory


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