One calculates energy-momentum tensor $T_{\mu\nu}$ from mass. However, is it possible to derive mass from the energy-momentum tensor?
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4$\begingroup$ You can produce an energy-momentum tensor for a particle from its mass density and its 4-velocity, yielding something like $T_{\mu\nu} = m \delta({\bf x}-{\bf x}_0) u_\mu u_\nu$. If the EM-tensor you have have the same overall shape, you can reverse-engineer the mass density, otherwise the best you can is look for the eigenvalue of the time-like eigenvector of the tensor, and call that your proper energy density, which you try to interpret as mass density. $\endgroup$– Hydro GuyCommented Feb 5, 2018 at 12:19
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$\begingroup$ @HydroGuy That looks like an answer, not a comment. $\endgroup$– sammy gerbilCommented Feb 5, 2018 at 15:31
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$\begingroup$ Ok. Thanks! What do you mean by the time-like eigenvector of the tensor? $\endgroup$– physics_2015Commented Feb 5, 2018 at 19:42
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