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Homework Help: String theory question

  1. Sep 20, 2007 #1
    1. The problem statement, all variables and given/known data
    For problem 6.5 I did a lot of manipulation and I get that the following holds at the endpoints of an open string:

    [tex]c = |\frac{\partial{\vec{X}}}{\partial{t}}| [/tex]

    This probably seems like silly intuitive queston, but I cannot explain why this implies that the string endpoints move at the speed of light. Since X is a four-vector not a three-vector, why can we draw that conclusion?

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
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