This expression, in which kB stands for the Boltzmann constant,
A the area of the horizon, and lpl =
G¯h/c3 the Planck’s length,
points to a deep connection between gravitation, thermodynamics,
and quantum mechanics, still far from being fully unveiled though
progress in that direction are being made—see, e.g., [4,5] and references
therein. Recently it was demonstrated that cosmological
apparent horizons are also endowed with thermodynamical properties,
formally identical to those of event horizons