Systems of Particle 4-Vectors

In the previous section we considered single 4-vectors and we classified them in timelike, spacelike and null according to their Lorentz length. In this section we consider sets of 4-vectors and in particular the timelike and the null 4-vectors which with one name we shall refer as particle 4-vectors.Particle 4-vectors  We will study the geometric properties of sets of these vectors which subsequently we shall use in order to describe the relativistic reactions. We emphasize that the present discussion is purely geometric and has not a priory any relation with Special Relativity.