  The issues of holography and possible links with gauge theories in spacetime
physics is discussed, in an approach quite distinct from the more restricted
AdS-CFT correspondence. A particular notion of holography in the context of
black hole thermodynamics is derived (rather than conjectured) from rather
elementary considerations, which also leads to a criterion of thermal stability
of radiant black holes, without resorting to specific classical metrics. For
black holes that obey this criterion, the canonical entropy is expressed in
terms of the microcanonical entropy of an Isolated Horizon which is essentially
a local generalization of the very global event horizon and is a null inner
boundary of spacetime, with marginal outer trapping. It is argued why degrees
of freedom on this horizon must be described by a topological gauge theory.
Quantizing this boundary theory leads to the microcanonical entropy of the
horizon expressed in terms of an infinite series asymptotic in the
cross-sectional area, with the leading `area-law' term followed by finite,
unambiguously calculable corrections arising from quantum spacetime
fluctuations.
