Why we see more diverging light rays than converging light rays? While the apparent fact that there's more diverging light rays than convergings ones seems to be intuitive, mathematically I can't find a reason to be so.
More specifically, given a vector field of light rays $\overrightarrow{v}\left(x,y,z,t\right)$, we want to find its overall divergence, i.e integrating it along the whole space:
$\int \nabla\cdot\overrightarrow{v} dV\, = \oint_S \overrightarrow{v}\cdot d\overrightarrow{n}\,$
by the divergence theorem. This seems to suggest that the overall divergence of light rays in some space depends on the net light rays going out and in this space, which should be 0 for a closed space, and always positive if the rays are always being more divenging than converging.
Are there anything missing there? Or is there some better mathematical treatment on this matter?
 A: Yes, you are missing the second law of thermodynamics. It is related to entropy, the arrow of time, etc. (search wikipedia for great details). Basically, your scenario of equal diverging and converging rays will only happen at thermodynamic equilibrium.  The laws of physics are invariant to time reversal, but particular solutions are sensitive to the initial conditions. Our universe started far from thermodynamic equilibrium, and is evolving towards it. In the mean time, we will have a difference between  diverging and converging rays, and between a lot of other things that should be symmetrical (such as anything that will look weird in a movie shown backwards) 
A: I suspect one should first carefully define the terms 'diverging' and 'converging' light.  The local quantity $\nabla\cdot\vec{v}$ really gives the amount of light emitted/absorbed in the point.  Of course, if there are no light sources/absorbers inside some volume, the total flux through the surface is zero, and the quantity is actually everywhere zero.  It will be zero everywhere around a light source (though in everyday terms light rays around a light bulb are 'diverging'), or after a magnifying lens, where they would be normally called 'convergent'.
It is less trivial to write in a simple way the quantity which would characterize the 'converging'/'diverging' property of light.  The way to construct it would be the following-first, note that for a divergent-free vector field $\vec{v}=\nabla\phi(x)$.  Then the surfaces of constant $\phi$ would be wavefronts.  In any point they are normally curved.  Depending on where $\vec{v}$ is pointing related to the curvature of the wavefront, it would correspond either to converging or diverging light.
A: By the second law of thermodynamics the stars loose their energies into the space growing older.
But, in addition, the boundaries of our universe are expanding AT LEAST with the light-velocity. The energy (radiation) lost by the stars is not reflected back by these boundaries (and it is not sure whether such boundariesy exist). So, on the universal scale, the radiation is mostly outgoing.
Good luck!
