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Homework Help: Lorentz Time Transformation Problem

  1. Sep 21, 2011 #1
    1. The problem statement, all variables and given/known data

    1) An alien spacecraft flies past the Earth with a speed of 0.866 c., according to an earthbound observer. One year later that observer witnesses a newly discovered planet start to pass between the Earth and its star (an event known as a transit) 20 ly away. When and where would an observer aboard the ship say the transit started?

    x=20 ly
    t=1 y
    v= .866 c

    2. Relevant equations

    t'= (t-(vx/c))/(root(1-(v/c)^2)

    (Sorry, the math notation wouldn't work, anyways it's the Lorentz transformation for time).

    3. The attempt at a solution

    Plug in: (20-(.866*1/1))/(root(1-(.866/1)^2)


    t'= 38.268 years

    The problem is that this seems to say that an object speeding towards an event would see the event after the observer farther away (38.268 years rather than 20 years), which even in the context of special relativity doesn't make sense to me?

    Can anyone help me out here?
    Last edited: Sep 21, 2011
  2. jcsd
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