Sum of Spacelike Vectors: Always Spacelike?

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SUMMARY

The sum of any two spacelike vectors is not necessarily spacelike, as demonstrated by the example (t,x) + (t,-x) = (2t,0), which results in a null vector. This conclusion challenges the assumption presented in the homework problem from the General Relativity textbook. The discussion highlights the importance of considering the direction of the vectors involved when analyzing their sum in the context of spacetime geometry.

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  • Understanding of spacelike vectors in the context of special relativity
  • Familiarity with the concept of light-cones in spacetime
  • Basic knowledge of vector addition in a four-dimensional space
  • Experience with General Relativity principles and equations
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  • Study the properties of null and timelike vectors in spacetime
  • Explore the implications of vector addition in Minkowski space
  • Learn about the geometric interpretation of spacetime diagrams
  • Investigate the role of directionality in vector operations within General Relativity
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Students of physics, particularly those studying General Relativity, mathematicians interested in vector spaces, and anyone seeking to deepen their understanding of spacetime geometry and vector addition.

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Homework Statement


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...
http://books.google.com/books?id=xm...ts=aowTGAbHj6&sig=EIQ6_W2eCQmMnHVP0l6FH2dEehg

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.

Homework Equations


The Attempt at a Solution

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

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