# gravitational convergence of light

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?

• Very nice question +1. Do they spread because of quantum loop box diagrams? What about the polarization of the photons? – Diego Mazón Sep 21 '12 at 3:35
• – Diego Mazón Sep 21 '12 at 3:50
• There is an answer here: physics.stackexchange.com/q/182329 – Jimmy360 May 31 '15 at 22:25
• I think this is more relevant than the answer linked by Jimmy360: physics.stackexchange.com/a/6222/4552 – user4552 Sep 9 '17 at 23:22

## 1 Answer

I first considered this question when I was 8 years old. In the subsequent 32 years my self-arrived conclusion is this; Diffusion. A ray of light will diffuse via the usual suspects until it is absorbed by the universe. Even a ray traversing the entire universe will be scattered, deflected, and consumed/absorbed before it can re converge on itself gravitationally. If your postulation is that the only thing in that universe is the ray of light, then, as it travels it expands the universe as it goes, which could be an interesting consideration for the expanse of the universe accelerating as it contracts.

• This seems to be nonmathematical speculation with no grounding in scientific knowledge. – user4552 Sep 9 '17 at 23:22
• Your opinion is unproven. Sniping without proof is catty banter. – user5467 Sep 10 '17 at 0:19