- See also
A matter collineation (sometimes matter symmetry and abbreviated to MC) is a vector field that satisfies the condition,
where 
are the energy-momentum tensor components. The intimate relation between geometry and physics may be highlighted here, as the vector field 
is regarded as preserving certain physical quantities along the flow lines of , this being true for any two observers. In connection with this, it may be shown that every Killing vector field is a matter collineation (by the Einstein field equations (EFE), with or without cosmological constant). Thus, given a solution of the EFE, a vector field that preserves the metric necessarily preserves the corresponding energy-momentum tensor. When the energy-momentum tensor represents a perfect fluid, every Killing vector field preserves the energy density, pressure and the fluid flow vector field. When the energy-momentum tensor represents an electromagnetic field, a Killing vector field does not necessarily preserve the electric and magnetic fields.
See also
- Affine vector field
- Conformal vector field
- Curvature collineation
- Homothetic vector field
- Spacetime symmetries
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