HPS 0410 Einstein for Everyone Spring 2015

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Assignment 4: Origins of Special Relativity

For submission

Read the introduction and first two sections of Einstein's paper "On the electrodynamics of moving bodies." Read it slowly and reverently. This text is to modern physics what Genesis is to modern Judeo-Christianity and the Declaration of Independence is to US history.

1. Compare what is moving with respect to what in the magnet and conductor thought experiment in the two accounts you have: the one Einstein gives in his paper and the one in the chapter section, Magnet and Conductor. How do the two accounts differ?

2. What is the "definition of simultaneity" that Einstein describes in the first section of his paper? That is, what must be stipulated by definition according to Einstein if we are to be able to compare the timing of events at a point A and a point B of space?

For discussion in the recitation.

A. In the introduction, what is established by the magnet and conductor thought experiment? How do ether current experiments enter the discussion? What is "apparently irreconcilable" and why is it so? How is Einstein suggesting that he will solve the problem?

B. In Section 2, how does Einstein establish that observers in relative motion may disagree on the lengths of rods and the synchrony of clocks?

C. If the synchrony of different clocks is set by a definition, presumably freely chosen, then it would seem that any velocities measured by them are also a matter of freely chosen definition. So how can Einstein at the end of Section 1 say that the constancy of the speed of light is a universal constant "in agreement with experience"?

D. What role did the Fresnel ether drag hypothesis play in the 19th century understanding of experiments aimed at showing the motion of the earth through the ether?

E.The Michelson-Morley experiment failed to reveal the motion of the earth through the ether. How did H. A. Lorentz explain this failure? How did Einstein explain it?