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