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Homework Help: Sum of two spacelike vectors

  1. Oct 20, 2007 #1
    1. The problem statement, all variables and given/known data
    Is it true that the sum of any two spacelike vectors is spacelike? I spent forever on this problem (5.4 from the link) and I think not...

    Actually, I think it is clearly not true if you think about the light-cone. But go to the link and tell me if there is something I am missing.
    2. Relevant equations

    3. The attempt at a solution
    Last edited: Oct 20, 2007
  2. jcsd
  3. Oct 21, 2007 #2


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    It is very true that the sum of two spacelike vectors is not necessarily spacelike. Like, (t,x)+(t,-x)=(2t,0) where (t,x) is spacelike. It's not clear to me what the author is thinking about.
  4. Oct 21, 2007 #3

    Meir Achuz

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    He must mean in the same direction. In any event it is a silly problem for a GR book.
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