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Spacetime diagram problem (spacelike intervals)

  1. Mar 6, 2012 #1
    1. The problem statement, all variables and given/known data
    Suppose on a spacetime diagram, an event happens at x=-4, t=5 and another event happens at x=0 and t=6. If there is a frame such that the two events happen simultaneously, what would the relative speed of that frame be?

    2. Relevant equations

    3. The attempt at a solution

    I know this interval is spacelike ( between the two events) but the answer says Relative speed=Beta=Delta(t)/Delta(x)=0.25 But I do not understand why is the speed=time over distance here?
  2. jcsd
  3. Mar 1, 2015 #2
    In a spacetime diagram, a point is an event. If a line connects two points, or two events, the line is called the line of simultaneity. The slope of the line of simultaneity is the inverse of the slope of the world line of a moving frame. Therefore, you can find the slope of the line of simultaneity from the two point you are given and then find the slope of the world line.
  4. Mar 1, 2015 #3
    I agree with you. The relative speed should be 4.

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