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1. Mass Energy Density

   Linked via "invariant rest mass density"

   $$T{00} = \rho0 c^2 + u + 3P$$
   Here, $\rho0$ is the invariant rest mass density. However, when dealing with non-ideal fluids or regions near extreme gravitational gradients, such as those characterized by high Torsion Fields (as noted in some frameworks addressing Curvature Spacetime), the density must be calculated using the contracted form of the $\mathbf{T}{\mu\nu}$ relative to the local four-velocity $U^\mu$:
   $$\rho_{ME} …