Several independent semiclassical arguments converge on $$\boxed{\Delta A=8\pi l_{\mathrm{Pl}}^2}, \qquad l_{\mathrm{Pl}}^2=\frac{G\hbar}{c^3}$$ I got interested in this reading the 2018 paper Bekenstein, I, and the quantum of black-hole surface area . Even though I disagree with Hod, its a great paper. Honourable mentions also go to: The Physical Interpretation of the Spectrum of Black Hole Quasinormal Modes , 2008 The Off-Shell Black Hole , 1994 On Black Hole Spectroscopy via Adiabatic Invariance , 2012 An Analytical Computation of Asymptotic Schwarzschild Quasinormal Frequencies , 2003 Asymptotic Black Hole Quasinormal Frequencies , 2003 1. Horizon Action Near any nonextremal horizon, imaginary time turns the normal geometry into a plane: $$ds_E^2\simeq d\rho^2+\rho^2d\Theta^2+\cdots.$$ Smoothness requires one horizon cycle: $$\oint d\Theta=2\pi.$$ The gravitational action identifies the momentum conjugate to $\The...
$\Lambda$CDM and Holographic Dark Energy Holographic dark energy (HDE) starts from a simple thought: the energy inside a region of size $L$ shouldn't exceed that of a black hole of the same size. Saturate that bound, up to a dimensionless number $c$ (not the speed of light), and $$\rho_{\rm DE}=3M_p^2\frac{c^2}{L^2}, \qquad\text{i.e.}\qquad c=HL\sqrt{\Omega_{\rm DE}}.$$ Units $\hbar=k=1$, $M_p^2=1/8\pi G$, prime $=d/d\ln a$, flat universe, $\Omega_X=\rho_X/3M_p^2H^2$. Li's Model In Li's 2004 model, $L$ is the future event horizon , the farthest a light ray sent today will ever get: $$L_e=a\int_t^\infty\frac{dt'}{a(t')}, \qquad \dot L_e=HL_e-1.$$ Li took $c$ constant, giving $w_{\rm DE}=-\frac13\left(1+\frac{2\sqrt{\Omega_{\rm DE}}}{c}\right)$. And this is where the problems begin. With $c=1$ and $\Omega_{\rm DE,0}=0.6889$, $w_0=-0.887$, while Planck 2018 $w_0=-1.03\pm0.03$. Does not match observations! And any constant $c<1$ gives $w<-1$ (phantom) a...