I learned that stress-energy tensor is defined in first place to be a 16-component object [tex]T^{\mu\nu}[/tex], where the first row [tex]T^{0\nu}[/tex] tells the energy density current, and the three other rows [tex]T^{i\nu}[/tex] tell the momentum density currents.(adsbygoogle = window.adsbygoogle || []).push({});

The Carrol introduces a stress-energy tensor where off diagonal terms are zero, and [tex]T^{00}[/tex] and [tex]T^{ii}[/tex] (the same value for all i=1,2,3) have some fixed values. He then merely says, that "we can choose to call [tex]T^{ii}[/tex] the pressure". Okey, does this have anything to do with earlier pressure concept that we know from elementary physics? If it does, how do you justify that, because it doesn't seem very obvious to me. Those diagonal terms in the first place were supposed to be components momentum currents, and I don't see how they could be interpreted as pressure.

(This question continues were discussion in "photon gas and relativity" lead, but I didn't want to spoil the original topic with my own problems more.)

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# Stress-energy tensor and pressure

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