Bekenstein and the Holographic Principle: Upper bounds for Entropy
Using the Bekenstein upper bound for the ratio of the entropy $S$ of any bounded system, with energy $E = Mc^2$ and effective size $R$, to its energy $E$ i.e. $S/E < 2\pi k R/\hbar c$, we combine it with the holographic principle (HP) bound ('t Hooft and Susskind) which is $S \le \pi k c^3R^2/\hbar G$. We find that, if both bounds are identical, such bounded system is a black hole (BH). For a system that is not a BH the two upper bounds are different. The entropy of the system must obey the lowest bound. If the bounds are proportional, the result is the proportionality between the mass M of the system and its effective size $R$. When the constant of proportionality is $2G/c^2$ the system in question is a BH, and the two bounds are identical. We analyze the case for a universe. Then the universe is a BH in the sense that its mass $M$ and its Hubble size $R \approx ct$, t the age of the universe, follow the Schwarzschild relation $2GM/c^2 = R$. Finally, for a BH, the Hawking and Unruh temperatures are the same. Applying this to a universe they define the quantum of mass $\sim 10^{-66} g$ for our universe.