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Einstein's 1905 papers

  1. May 25, 2005 #1
    It occurs to me that as audacious as Einstein's relativity and photoelectric effect papers were 100 years ago, taken together they're even more so.

    The relativity paper is fundamentally grounded in the electromagnetic wave theory of light, yet at the same time he had decided that this theory of light was inadequate. How could he have known that once all the details of his particle theory of light were ironed out, that the speed of photons would have to be the same in all frames? But he did. What a guy!
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  3. May 28, 2005 #2
    Dr. Einstein was very sure he was correct. He related SR to Maxwell's equations and Doppler's Principle and aberration. Lorentz on the other hand, had simply developed an ad hoc system, that when confronted with skepticism, he was willing to back away from.

    But Einstein was very sure, and when Kaufmann's experiment of 1906 did not seem to support Relativity, Einstein thought it in error, but Pointcare said, "The principal of Relativity may well not have the rigorous value which has been attributed to it." An experiment in 1908, by Alfred Bucherer confirmed Einstein's suspicions.

    This seems totally amazing when Einstein hoping to be finally admitted to graduate school at his old polytechnic, sent his 1905 paper to them and it was dismissed as "incomprehensible."

    Einstein put emphasis on a "thought experiment" at 16 where he was mentally racing a light beam. This from someone who as a boy had a teacher who considered him retarded and thought he should be removed from school.

    It is difficult to make conclusions about the mind of Einstein, but it is entirely wrong to think that SR was just an ad hoc guess or a blind shot in the dark.
    Last edited: May 28, 2005
  4. Jun 3, 2005 #3
    Einstein had worked on the Theory “off” and “on” since he was 16, starting while he was still a student. For ten years he tried and abandoned many fruitless attempts, but in his own words: “the problem was always with me.” Gradually he began to suspect “time” as the rapscallion.

    “A normal adult never stops to think about problems of space and time. These are things which he has thought about as a child. But my intellectual development was retarded, as a result of which I began to wonder about space and time only when I had already grown up.”
  5. Jun 3, 2005 #4
    THe photons were quanta of light. Had they not had the same speed as light then something would have been seriously wrong.

  6. Jun 4, 2005 #5

    I'm not saying it could have turned out that photons don't travel at the speed of light. As you say, that would make no sense. But why did it have to turn out that the speed of photons is the same in all inertial frames? That had only been demonstrated by assuming that light was a wave.
  7. Jun 5, 2005 #6


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    I think Einstein got there by "reverse engineering" the Lorentz transformations. He knew that they were what he wanted to prove/derive, and it guided him to the assumptions he would have to make. Actually Einstein's original paper doesn't assume it: he uses a different postulate, that the speed of light is independent of its source's speed (assumed constant). Secondly, Einstein was still thinking of light as a wave; it was light's interaction with matter that he showed to be quantized in his photoelectric paper. The title of the relativity paper refers to electrodynamics.
  8. Jun 5, 2005 #7
    Actually that's an axiom we have to accept since its borne out by experiment. There is nothing in physics which says that a photon must have zero rest mass. Had the universe all of a sudden changed and we had photons with non-zero rest mass then Maxwell's equations would be alterered. The Lagrangian for this Modified Maxwell equation is known as the "Proca Lagrangian." The "speed of light" axiom would then need to be dropped and only the principle of relativity would remain.

  9. Jun 5, 2005 #8


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    The "speed of light" axiom would probably be replaced by something equivalent to a "maximum signal speed" axiom.
  10. Jun 5, 2005 #9
    Well, I can't really argue with that, because he did publish both theories, and they both turned out to be right!

    But my original point was that in one paper he assumes a wave model for light and arrives at a revolutionary result (relative simultaneity). Then in the other paper he launches a serious challenge to that very wave theory of light. Planck had already shown that light acts like particles at its source; now Einstein thinks it acts like particles when it gets where it's going. But he's so sure that in between it acts like a wave, he's willing to say that everyone's been wrong about absolute simultaneity.

    I think I would have hesitated and thought, "if it's particles at the beginning and particles at the end maybe it's particles all the way." And particles usually travel at constant speed wrt their source. And that model would have been consistent (at least superficially) with the null result of the Michelson and Morley experiment. But of course, I would have been wrong!
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