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The background to and essentials of special relativity

The background to and essentials of special relativity. Rory Makielski, Sally Salvador March 28, 2006. Albert Einstein. 1879 – 1955 Modern scientific genius Humanitarian. The early years. Born in Ulm, Germany Early education was too oppressive Early interest in science Compass needle

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The background to and essentials of special relativity

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  1. The background to and essentials of special relativity Rory Makielski, Sally Salvador March 28, 2006

  2. Albert Einstein • 1879 – 1955 • Modern scientific genius • Humanitarian

  3. The early years • Born in Ulm, Germany • Early education was too oppressive • Early interest in science • Compass needle • “Something deeply hidden had to be behind things.” • Euclidean geometry • “This lucidity and certainty made an indescribable impression upon me.”

  4. Accomplishments • 1900- earns degree from Swiss Federal Polytechnic School in Zurich • 1901- claims Swiss citizenship, works as patent examiner • Michelangelo Besso (1873 – 1955) • 1905 – publishes dissertation on determining molecular dimensions and four more papers

  5. Annalen der Physik • “On a Heuristic Viewpoint Concerning the Production and Transformation of Light” • Describes photoelectric effect based on light quanta (Nobel Prize, 1921) • “On the Movement of Small Particles Suspended in a Stationary Liquid Demanded by the Molecular Kinetic Theory of Heat” • Brownian motion, existence of atoms • “On the Electrodynamics of Moving Bodies” • Special theory of relativity • “Does the Inertia of a Body Depend Upon Its Energy Content?” • Equivalence of energy and matter

  6. Duality of personality • Poor student, but interested in science • passion for social justice but lacked personal relationships and state loyalty • Indifferent toward outside opinion

  7. The Humanitarian • Pacifist, democratic socialist • Zionism • Used scientific prestige to promote his social cause • Anti-Einstein groups • 1930’s, Hitler purges universities of Jews • 1939, urges FDR to develop atom bomb • Civil Rights Movement

  8. Religious & Philosophical Influences • "I believe in Spinoza’s God who reveals himself in the orderly harmony of what exists, not in a God who concerns himself with the fates and actions of human beings." • Logical positivism • Free invention of mind + experiments = general theories • Hume, Mach, Poincaré • Skeptical, critical

  9. Skepticism on Classical Physics • Maxwell, Lorentz • Asymmetry between reference frames • Gedankenexperiment

  10. “Simultaneity” • Definition of Simultaneity based on round trip of light from A to B • Assumes constancy of c • Leads to Lorentz transformations (discussed later)

  11. Constant Speed of Light? • The speed of light is defined as being independent of the direction of propagation • This is merely a convention, not provable experimentally • Other possibilities exist (such as the speed being constant for round trip)

  12. First Assumption • “The laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems of coordinates in uniform translatory motion” • The laws of physics the same in all inertial frames

  13. Second Assumption • “Any ray of light moves in the “stationary” system of coordinates with the determined velocity c, whether the ray be emitted by a stationary or by a moving body” • The speed of light has the same value for all observers

  14. Dilemma for Classical Mechanics • Newton’s laws of motion • Maxwell’s equations • Classical concepts of space time • Taken together, imply that it must be possible to determine the velocity of an observer relative to light • Not consistent with Einstein’s postulates

  15. Einstein’s Resolution • Maxwell’s equations correct • Classical mechanics incorrect when v approaches c • No aether, no absolutes

  16. 1905 Relativity Paper • Profound and remarkable despite no references to contemporary research • Only acknowledgement to Besso • Theory of principle (Einstein) vs. constructive theories (Lorentz)

  17. Time Dilation/Length Contraction • http://www.phys.unsw.edu.au/einsteinlight/ • Proper times are dilated- a clock moving close to the speed of light will appear to run more slowly to a “stationary” observer • Moving objects will appear shorter

  18. Direct Confirmation • Bruno Rossi confirms time dilation for high speed radioactive particles in 1941

  19. Lorentz Transformations • Used to transcribe an event in one inertial frame to another • When v/c <<1, Newtonian transformation applies x’= γ(x-vt) or x’=x-vt for Newton y’=y z’=z t’= γ(t-vx/c2) or t’=t for Newton γ = 1/(√1-(v/c)2), approaches 1 for low velocities

  20. “I have no particular talent, I am merely extremely inquisitive.”

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