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## Main Question or Discussion Point

**J Baez' "The meaning of Einstein's Equations"**

Hi All,

I am trying to study the paper of Jonh Baez in the july editon of Am. J. of Phys. on the meaning of Einstein's equation.

At a given point he says:

"The components of [itex]T_{\alpha \beta}[/itex] (stress-energy tensor) say how much momentum in the [itex]\alpha[/itex] direction is flowing in the [itex]\beta[/itex] direction through a given point of space-time, where [itex]\alpha \beta[/itex] = t, x, y, z. The flow of x-momentum in the x-direction is the pressure in the x-direction denoted [itex]P_x[/itex], and similarly for y and z. It takes a while to figure out why pressure is really the flow of momentum, but its eminently worth doing."

Does anybody know how to prove this last statement.

Thank you in advance

Sincerely,

DaTario

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