1. In our expression for the metric, note that are null vector fields. 2. Note that if and, then, so that is a null vector . 3. Null vectors are also used in the Newman Penrose formalism approach to spacetime manifolds.4. They are distinguished in that only for the latter there exists a nonzero null vector . 5. The four-frequency of a photon is always a future-pointing and null vector . 6. The set of all null vectors at an event of Minkowski space constitutes the light cone of that event. 7. They are normal vector can be expressed as a linear combination of two future directed null vectors , normalised by: 8. In general the norm of a composition algebra may be a quadratic form that is not definite and has null vectors . 9. Over the reals, if two null vectors are orthogonal ( zero Minkowski tensor value ), then they must be proportional. 10. The coefficients of the linear combination are determined so to best approximate, in a least squares sense, the null vector .
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