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Einstein's train thought experiment

  1. Nov 15, 2013 #1

    Why did they define the lightning event to be simultaneous for Stanley? Why can't it be simultaneous for Mavis, so that the lighting hits A first?
  2. jcsd
  3. Nov 15, 2013 #2


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    In that case Stanley would conclude the two lightning strikes were not simultanous in his frame of reference.

    As for
    , that statement has to have a qualifier of which frame of reference you are referring to - that of either Stanley's or Mavis's or perhaps of another viewer in another inertial frame of reference who might not agree with Mavis or Stanley.
  4. Nov 15, 2013 #3
    Oh I see now. The book simply said two lightings hit A and B at the same time, but now I understand they obviously were talking from Stanley frame of reference.

    I'm still stuck in the newtonian way of viewing things.

    Last edited: Nov 15, 2013
  5. Nov 15, 2013 #4


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    Where did the book say that? I thought the whole point of the explanation in the book was that at the same time, in other words, simultaneity, "depends on the frame of reference".

    [There is an error in the second drawing, (b), where they show the points A' and B' having moved to the right, but they don't show the train and Mavis also moving, like they show in the two drawings below it.]

    By the way, this thought problem is similar to the one presented by Einstein in 1920 but there you will see that Einstein specifically states that the lightning strokes "are simultaneous with reference to the railway embankment". He also specifically states that the observer on the train is at the midpoint between the lightning strikes (not necessarily the midpoint of the train).

    Does your book go into these details in a part earlier than where you photographed?
  6. Nov 15, 2013 #5
    They mentioned "suppose the wave-fronts reach Stanley simultaneously" which implies simultaneousness from Stanley's POV, so yes they did say it but I missed it in the wall of text, and got confused.
  7. Nov 15, 2013 #6


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    Good, did they also say anything about the observers being at the midpoint of the lightning strikes?
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