Derivation of Stress-Energy (Energy-Momentum) Tensor for Perfect Fluid

1. May 6, 2013

I am trying to derive this result:

$T_{αβ} = ( ρ + \frac{p}{c^{2}} ) U_{α} U_{β} - p g_{αβ}$

The energy-momentum (stress-energy) tensor for a perfect fluid.

I do not know where to start and don't understand some derivations of this result.

In particular, I don't understand why some derivations on the internet use the concept of relativistic mass and how it relates to density. I think I'm sure that mass is a Lorentz scalar and is invariant.

Also, how does it play a part in Einstein's equation?