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Einstein; The principle of relativity and the law of propagation of light. 
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#1
Dec1607, 02:36 PM

P: 1

1. The problem statement, all variables and given/known data
2.Explain in your own words what Einstein means by “the principle of relativity”, and why it seems to be incompatible with the theory of electromagnetism (or “the law of propagation of light”). 2. Relevant equations Not an equation but Einsteins answer can be seen here in section 7 http://en.wikisource.org/wiki/Relati..._of_Relativity 3. The attempt at a solution Alright, here's my attempt. I'm posting it here because I get the feeling I may have entirely missed the point Einstein was trying to put across, and would like correcting if that is the case... Einsteins “Principle of relativity”, is that for a Galileian coordinate system moving relative to another Galileian coordinate system (used as the reference body) in a straight line, the general laws of physics apply relative to the moving coordinate system in the exact same way as they do with respect to the reference body coordinate system. However the Dutch astronomer De Sitter, by observing double stars, was able to show that the velocity of propagation of light cannot depend on the velocity of motion of the body emitting the light. Therefore, applied to the principle of relativity, if light is traveling relative to the reference body coordinate system in the same direction as the moving coordinate system, then as viewed from the moving coordinate system the light would be traveling at the accepted velocity of light minus the velocity of the moving coordinate system (ie; slower than the speed of light). So the law of propagation of light could not apply to both the stationary coordinate system and the moving coordinate system, so either the principle of relativity or the law of propagation of light must be wrong. It's pretty badly worded at the moment, but I'd just like to know if my explanation is along the right lines. The deadline for this question is tomorrow afternoon so help before then would be much appreciated. 


#2
Dec1907, 12:32 PM

P: 1,778

Well, Maxwell's Equations (on which the whole theory of classical electrodynamics is based) are invariant under Lorentz Transformationsthe transformations of Special Relativity. Classical Electrodynamics is thus completely consistent with Special Relativity. Galilean transformations follow from Lorentz Transformations in the low speed limit.



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