Sum of two spacelike vectors

1. Oct 20, 2007

ehrenfest

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. Oct 21, 2007

Dick

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.

3. Oct 21, 2007

Meir Achuz

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