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I Why was it needed to search ether frame?

  1. May 30, 2017 #1
    From the book - Introduction to special relativity, Robert Resnick, I learnt that
    it was assumed at that time that speed of light is c in ether frame.
    And so, there was a need to find out ether frame.
    I am assuming that ether frame is an inertial frame .
    Speed of light in vacuum could have been measured from different inertial frames and it could have been known that Galilean transformation doesn't work in this case.
    This itself will lead to the search of another transformation.
    Now, even if we get the ether frame , what we will know is speed of light in ether frame as well as in all other inertial frames is c, which is not a new information.
    So, was the ether frame being searched for the purpose of getting an absolute frame?
    Or, was ether being searched for the purpose of getting a medium in which speed of light is c?


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  3. May 30, 2017 #2


    Staff: Mentor

    That was not known at the time. The experiments had to be performed to demonstrate this.
  4. May 30, 2017 #3
    So, at that time it was thought that speed of light in vacuum would be different for different initial frames (according to Galilean relativity ) and there exists one inertial frame in which speed of light is c ; so , there was a need to search for this inertial system known as ether system.
    Then , they had no idea that speed of light could be same in all initial frames and so they couldn't think of doing an experiment to verify this idea.
    Is this correct?
    Then , how did Einstein get this idea?
  5. May 30, 2017 #4


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    Staff: Mentor

    I think maybe you have it backwards? It was believed that the aether frame existed, but the experiment showed that it didn't (at least in the way believed).

    Historically, I'm not sure if Einstein knew about the unsuccessful experiment, but there are other ways he could have thought the aether was unnecessary, such as the implication that Maxwell's equations should be frame dependent if there was an aether.
  6. May 30, 2017 #5
    O.k. thank you.
  7. May 30, 2017 #6


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    2017 Award

    It's, most probably, a legend that Einstein came to his famous "Electrodynamics of moving bodies" paper (1905) due to the Michelson-Morley negative result to observe the "ether wind".

    It was the lack of symmetry in the point of view on Maxwell's electrodynamics, which was not observed in nature, that brought him to the idea to have to adapt the space-time description to make the Maxwell equations symmetric against "boosts" (i.e., the change from one inertial frame to another moving against it with constant velocity). If the Maxwell equations are forminvariant, then the speed of light in vacuo must stay the same in all frames (that's evident in Gaussian units immediately, as was common sense in Einstein's time; the pest of the SI in theoretical electrodynamics textbooks is a rather new phenomenon). This point of view brought him to give a foundation of relativistic space-time, which formally was known at least 20 years earlier, when Voigt has come up with something very close to what's called Lorentz transformations nowadays, but at this time has been interpreted only as a mathematical trick rather than establishing a new description of the entire space-time structure. Then this idea was very quickly finalized by Minkowski's mathematical analysis in terms of a pseudo-Euclidean affine four-dimensional manifold.

    However, only 10 years later, in 2015, Einstein again modified the description of the space-time manifold in including gravity into the relativistic point of view, leading finally to the General Relativity Theory, which is the best space-time description known today.
  8. May 30, 2017 #7
    O.k. So, the idea that speed of light in vacuum is same in all reference frames comes from the fact that Maxwell equations should remain covariant in all inertial reference frames.
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