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Einstein's train (simultaneity)

  1. Oct 20, 2011 #1
    1. The problem statement, all variables and given/known data

    We have an observer moving along a moving train car with speed v (assumed to be relative velocity between observer and car). Two light signals are emitted from each end of the car.

    a)Where is the observer if he sees both signals simultaneously?
    b)From his point of view, which signal was sent first?

    2. Relevant equations

    3. The attempt at a solution

    I simply took the frame in which the observer is at rest and said the train is moving past with speed v. This is the typical Einstein's train scenario with the observer on the platform (except the train is pretty slow). So our observer must be passing the middle of the train when he sees the lights.

    But why the second part of the question? So I must be wrong.
    Last edited: Oct 20, 2011
  2. jcsd
  3. Oct 20, 2011 #2


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    Homework Helper

    Have you considered the possibility "neither, they were sent at the same time"
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