Class23HO - Class 23 The Foundations of Relativity Physics...

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Class 23 The Foundations of Relativity Physics 106 Fall 2011 Press CTRL-L to view as a slide show.
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Last Time Last time we discussed: I Uncertainty Principle Problems I Development of Atomic Models I The Bohr Model (some things are right) I The Schrödinger Model (almost right)
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Learning Outcomes Today we will discuss: I The Need for Relativity I What Is Relativity? I The Postulates of Relativity I Terminology I How Newtonian Mechanics Differs from Relativistic Mechanics
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The Need for Relativity
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Luminiferous Ether I 19 th Century physicists thought that electromagnetic waves were mechanical waves that travel through a medium I The medium was called the luminiferous ether or just the ether I Present everywhere, even in empty space I Massless, but rigid medium I Could have no effect on the motion of planets or other objects
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The Speed of Light in the Ether I The speed of light is c in the ether if the ether is at rest. I The speed of light on earth depends on the velocity of the earth in the ether
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Michelson-Morley Experiment I First performed in 1881 by Michelson I Repeated under various conditions by Michelson and Morley I Designed to detect small changes in the speed of light
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Michelson-Morley Equipment I Used the Michelson Interferometer I If the velocity of light were different in different directions, the fringes would change as the interferometer was rotated through 90
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Michelson-Morley Results I Measurements failed to show any change in the fringe pattern I The "null result" was explained by saying the earth dragged the ether along with it. I But why then don’t planets slow down in the viscous drag of the ether?
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Michelson-Morley Results I In 1904, H. A. Lorentz proposed a set of laws that described how electric and magnetic fields appeared to observers in different inertial frames I These were called the Lorentz transformations I The Lorentz transformations suggested that all observers would measure the speed of light to be the same.
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Albert Einstein I 1879 -1955 I 1905 published four papers, two on special relativity I 1916 published about General Relativity I Searched for a unified theory of all forces
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The Beginning of Relativity I In 1905, Albert Einstein published his paper "On the Electrodynamics of Moving Charges" I He suggested that the Lorentz transformations described fundamental characteristics of space-time, not just electric and magnetic fields I Later in 1905 he showed how mass must vary with velocity and introduced the relation E = mc 2
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What Is Relativity?
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Two Theories of Relativity I Special Relativity - 1905 I A theory of flat space and time I Describes how observers moving at different speeds measure physical quantities I General Relativity -1916 I A theory of gravity I Describes how matter changes the curvature of space and time, and how matter behaves in curved space and time.
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New Terminology I Reference frame I Inertial reference frame I Event I Space-time I Rest energy and total energy
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