Causal types of orthogonal four-vectors
= Causal types of orthogonal four-vectors
A nonzero <Lorentz four-vector> orthogonal to a <timelike vector> is spacelike: in the latter's rest frame the former has zero temporal component. Orthogonality alone does not ensure one timelike and one spacelike vector. Two orthogonal spatial coordinate vectors are both spacelike, and parallel <null vectors> are also orthogonal.