  The holographic property of entropy plays a key role in the thermodynamic
description of gravitational field equations. It remains unclear, we argue,
whether this property is necessarily interwoven with gravity itself or can be
understood instead as a manifestation of physics outside gravity.
  It is pointed out that if the latter is the case, so that the holographic
property of entropy could be considered as completely rooted on some
microscopic, non-gravitational, intrinsic property of matter, gravity could
merely be understood as the necessary macroscopic manifestation of this
microscopic property of matter, being simply the expression of the
thermodynamic conservation of energy. A quite peculiar status of Einstein's
gravity in this context (as compared to generalized metric theories of gravity)
is apparent. A successful microscopic property of matter, is found to
necessarily mean in particular the existence of an absolute minimum wavelength
for photons, of orders of Planck length.
