Lecture_32

# Lecture_32 - PHYS 342 Fall 2011 Lecture 32 The...

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PHYS 342 Fall 2011 Lecture 32: The Lorentz-Einstein Transformation Equations Ron Reifenberger Birck Nanotechnology Center Purdue University Lecture 32 1

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Michelson-Morely – most famous null experiment in history Lower limits on ETHER drift velocity: Initially (1881) < 5 km/s More refined < 1.5 km/s New experiments < 3 m/s Conclude that speed of light is constant in all inertial reference frames! What Next?? http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/mmexpt6.htm 2
Historically, two solutions emerge Einstein (1905) Focus on E&M: Faraday's results are Voight (1887) Larmor (1900) Lorentz (1904) Keep “ether” concept C k f i Focus on E&M: Faraday s results are frame invariant! Cook up transformations to be consistent with M-M experiment Implies i) laws of E&M do not depend on Believed the transformations were just a math trick for manipulating Maxwell’s Eqs. frame of reference, AND ii) speed of the fields that propagate between magnet and loop t b i d d t f th must be independent of the velocity of the reference frame. Derives same transformations as Lorentz Leads to Special Relativity 3

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Einstein’s Approach ! induced in the loop is the same E y & Laws of E M must be frame invariant S y x S x v v x B B B A t    E 4
Both approaches tangle space with time. But…. What is Space? Space is what we measure with a measuring rod What is Time? Ti i h i h l k Time is what we measure with a clock What are the new transformation equations between fixed and moving co-ordinate systems so that the velocity of light is same in both systems? Something has to “give” and what “gives” is space and time. Effectively, space and time now become a function of speed. 5

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