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Michelson-Morely Experiment

  1. Feb 25, 2005 #1
    What was the objective of the MME?
    Did the Lorentz contraction actually explain the null result of the MME?
  2. jcsd
  3. Feb 25, 2005 #2


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    The Michelson-Morely experiment was set up to test the (at the time) rather unexpected prediction of Maxwell's equations that the speed of light in vacuum is constant and independant of the frame of reference.

    Alternatively, it could be looked at as an attempt to measure the speed of the 'luminus ether wind'.
  4. Feb 25, 2005 #3


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    The original objective was to show that the speed of light was different moving in the direction of the hypothetical ether wind than it would be moving across at a right angle to the ether wind. If ether really existed, it would be unreasonable to believe that it travels along with the earth at all times of the year. You would expect the planet to be moving through it at some time of the year, if not all the time.

    Since the observers were moving along with the apparatus, I don't think so.

    What explains the null result of the MME is that there really is no ether that is the medium of which light travels. If one could set up an MME but with sound waves, it would show a positive result if the air was moving passed and through the apparatus. That's because air is the medium in which sound propagates. There is no such medium for electromagnetic waves.

    r b-j
  5. Feb 26, 2005 #4
    According to M+M, the purpose of their experiment was to test the validity of Fresnel's hypothesis that "the ether is supposed to be at rest except in the interior of transparent media." M+M concluded that their experiment indicated that, "...the relative velocity of the earth and the ether is probably less than one sixth of the eatth's orbital velocity, and certainly less than one-fourth".[The American Journal of Science, No. 203, Nov. 1887, p333.]

    If one applies the Lorentz contraction to M+M's math (in the cited article), it does not explain the results of the experiment.

    Why did the MME produce the result that it did?
  6. Feb 26, 2005 #5


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    the only curiosity to me is why they would expect the "the relative velocity of the earth and the ether [to be] certainly less than one-fourth" earth's orbital velocity at all times of the year. if the earth happened to be moving along with the ether wind in spring, it should be moving rapidly through it in the fall. the only reason to suspect not would be some wild theory that the ether wind moves along side of the earth wherever it is, as if the earth is the center of all things.

    i have absolutely no idea why anyone would be applying any Lorentz transformation to the experiment at all. is the observer moving relative to the apparatus?

    isn't the ostensible answer obvious? you need to read what responses given you previously.

    when an experiment turns out different than the expectation, the first thing to do is double and triple check the procedure to make sure you did it right. and then rerun it to see if the previous result was spurious. i think that "M+M" did that multiple times. if you've conceived the experiment properly and carried out carefully and without error, and it turns out opposite of theory, it's time to recheck the theory and the underlying assumptions of it.

    r b-j
  7. Feb 26, 2005 #6


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    Staff: Mentor

    HannonRJ, if you already [think you] know the answer to your questions, what is the purpose of this thread?
  8. Mar 10, 2005 #7
    "i have absolutely no idea why anyone would be applying any Lorentz transformation to the experiment (Michelson-Morley) at all. is the observer moving relative to the apparatus?"

    Your comment implies that you accept the tenets of relativity. If that is the case, then you would expect a null result from the experiment, knowing that the velocity with which your frame is moving has no effect on observations within your frame. However, if you believe that Galilean transformations apply, then you would expect a non-null result as Michelson did.
  9. Mar 11, 2005 #8

    Andrew Mason

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    The question relates to the Lorentz contraction (actually first thought up by Fitzgerald, so it is also known as the Fitzgerald-Lorentz contraction), not the Lorentz transformation. The Fitzgerald- Lorentz contraction did explain the MME result. The problem was that no one could explain why distances would contract in the direction of the motion through the ether by exactly the right amount needed to make the speed of light appear to be equal in all directions.

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