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## Main Question or Discussion Point

The observer and the object has the same four-velocity U^u as (1,0,0,0),which means they are relatively static.Then the the observer measures a point A of the object's enery density,which is ρ.

My question is,the ρ is T^00 or T_00 at the point A?

My question is,the ρ is T^00 or T_00 at the point A?