Solution
= Solution
Use $x^0=ct$. The <stress-energy tensor> component $T^{00}$ is energy per unit volume; $cT^{i0}$ is energy flux in direction $i$; $T^{0j}/c$ is momentum density in direction $j$; and $T^{ij}$ is the flux of momentum component $j$ through a surface normal to direction $i$. In a symmetric tensor, energy flux equals $c^2$ times momentum density. Thus $\partial_\mu T^{\mu0}=0$ is energy conservation and $\partial_\mu T^{\mu j}=0$ is momentum conservation.