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light has a non-zero energy-stress tensor, so a flux of radiation will slightly affect curvature of spacetime

Question: assume a flux of radiation in the $z$ direction, in flat Minkowski space it will propagate and spread slightly in the $x$ and $y$ directions. But what happens if we take into account self-gravitational effects of light onto itself? will the radiation flux self-gravitate and eventually reconverge?

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Very nice question +1. Do they spread because of quantum loop box diagrams? What about the polarization of the photons? –  drake Sep 21 '12 at 3:35
Related physics.stackexchange.com/questions/6197/… –  drake Sep 21 '12 at 3:50

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