How is information encoded in the Cosmological Horizon? It is my understanding, according to the "Holographic Universe Theory", that multi-dimensional volume somehow emerges from a two-dimensional surface called the "Cosmological Horizon". And all three-dimensional reality is extruded from encoded information in this horizon. Is this horizon a purely mathamatical construct, or is it a real, perhaps light-like boundary? If information is pre-encoded on this surface, who or what does the encoding? 
 A: The cosmological horizon is out at a distance of about 12 billion light years, which is about $1.2\times 10^{26}$m. This is then an area of $1.8\times 10^{53}m^2$. I will use Bekenstein's bound to estimate the entropy of the universe,
$$
S = k\frac{A}{4\ell_p^2} = 1.38\times 10^{-23}j/K\frac{1.8\times 10^{53}m^2}{2.5\times 10^{-66}m^2} 
$$
$$
= 1.38\times 10^{-23}j/K\times 7.0\times 10^{127}m^2 =  1.0\times 10^{105}j/K
$$
How do I get the energy? It will not work to multiply by the CMB temperature, for that is not the horizon temperature.The temperature is 
$$
T = \frac{\hbar c}{2\pi}\sqrt{\frac{\Lambda}{3}} \simeq 2.8\times 10^{-53}K, 
$$
where $\Lambda$ is the cosmological constant. I now multiply this by the entropy for $E = ST$ to get $E = 2.8\times 10^{48}kg$. The mass of a proton is $1.6\times 10^{-27}kg$, and I now divide this into the energy I obtain to get the number of protons which is $N = 1.8\times 10^{79}$ This is close to the actual estimate.
The particles and field in the volume contained in the space bounded by the cosmological horizon are equivalent to what we might assign to the holographic screen on the horizon. 
