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Michelson morley

  1. Aug 9, 2009 #1
    Could someone please explain to me the significance of the results of the michelson morley experiment? What is the explanation of how those results could happen and how they fit in with current theory? Has the experiment been repeated in space away from the earth's gravity field?
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  3. Aug 9, 2009 #2


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    Here's a primer, which, handily enough, is broken down into sections which correspond to your questions:

    It broke the pre-existing notion of a luminous aether (the medium which electromagnetic waves would propagate in), and thus established the current thinking that space is mostly a vacuum and that EM waves can sustain themselves (instead of needing a medium to travel through).
  4. Aug 9, 2009 #3
    I read that and it doesn't explain it to me.

    The earth is not the center of the universe, it is moving. The only explanation I can see is that it is dragging the light waves they used along with it for them to have an identical speed in every direction. That makes no sense to me. If EM has an inherit speed regardless of source and surroundings the movement of the earth would have shown an effect in the experiment.

    I have read every explanation of this experiment and it still doesn't make sense. Nothing I have read explains the experiments results to me, it seems paradoxical. It does not look like the experiment was done in space. I would also be interested to see the experiment done at one of the poles.
  5. Aug 9, 2009 #4


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    I don't understand, what does not make sense about it? The Earth does not drag light (well... outside of gravitational effects I guess but that isn't what I would call dragging). More to a point, the experiment helped to cement the idea that the Earth does not drag anything. If there was an (a)ether, then one of the theories was that the Earth could drag the ether. There were several ideas about the ether and the experiment was hoped to help quantify some of the ether's properties.
  6. Aug 9, 2009 #5
    The experiment proves that matter and confined light act the same way. For example, a ruler that retains its length by keeping a certain number of standing waves within, will act just like a ruler made of wood. The experiment doesn't actually prove there is no preferred inertial reference frame, as much literature claims. To do that you need two co-moving observers, and that wasn't what M-M did.
  7. Aug 9, 2009 #6


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    Special relativity provides a model that is compatible with the result.
  8. Aug 9, 2009 #7


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    Welcome to PF!

    Hi fillindablank! Welcome to PF! :smile:
    That's exactly the point!!

    The only way the M-M experiment can be compatible with an absolute space is if the Earth is dragging space along with it …

    since that's very unlikely (as you say, it "makes no sense"), that is fairly convincing argument against absolute space. :wink:

    (of course, there have since been plenty of experiments that have confirmed Special Relativity in other ways)
  9. Aug 10, 2009 #8

    The way the Michelson Morley experiment was set up determined categorically, that, if an aether existed, then the earth wasn't moving through it.
    However, no experiments were done to discount the possibility that the aether could be moving downwards towards the earth's centre. Also, to my knowledge, no experiments have been done in space, and by space they would need to be done in far space. I don't think it would be of any value doing them in an orbiting space station, for instance.
  10. Aug 10, 2009 #9
    And the experiment was designed under the assumption that matter did not act like confined light--which turned out to be wrong! (Matter acts exactly like confined light. For example, you can't tell a box of light from a box of matter without opening the box). All MM proved is that matter acts like confined light. It does not prove there is no preferred IRF, as is always claimed about the experiment. You need a different experiment to prove that.
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