  Gravity is a macroscopic manifestation of a microscopic quantum theory of
space-time, just as the theories of elasticity and hydrodynamics are the
macroscopic manifestation of the underlying quantum theory of atoms. The
connection of gravitation and thermodynamics is long and deep. The observation
that space-time has a temperature for accelerating observers and horizons is
direct evidence that there are underlying microscopic degrees of freedom. The
equipartition of energy, meaning of temperature, in these modes leads one to
anticipate that there is also an entropy associated. When this entropy is
maximized on a volume of space-time, then one retrieves the metric of
space-time (i.e. the equations of gravity, e.g. GR). Since the metric satisfies
the extremum in entropy on the volume, then the volume integral of the entropy
can readily be converted to surface integral, via Gauss's Theorem. This surface
integral is simply an integral of the macroscopic entropy flow producing the
mean entropy holographic principle. This approach also has the added value that
it naturally dispenses with the cosmological constant/vacuum energy problem in
gravity except perhaps for second order quantum effects on the mean surface
entropy.
