  The formalism of Holographic Space-time (HST) is a translation of the
principles of Lorentzian geometry into the language of quantum information.
Intervals along time-like trajectories, and their associated causal diamonds,
completely characterize a Lorentzian geometry. The
Bekenstein-Hawking-Gibbons-'t Hooft-Jacobson-Fischler-Susskind-Bousso Covariant
Entropy Principle, equates the logarithm of the dimension of the Hilbert space
associated with a diamond to one quarter of the area of the diamond's
holographic screen, measured in Planck units. The most convincing argument for
this principle is Jacobson's derivation of Einstein's equations as the
hydrodynamic expression of this entropy law. In that context, the null energy
condition (NEC) is seen to be the analog of the local law of entropy increase.
The quantum version of Einstein's relativity principle is a set of constraints
on the mutual quantum information shared by causal diamonds along different
time-like trajectories. The implementation of this constraint for trajectories
in relative motion is the greatest unsolved problem in HST. The other key
feature of HST is its claim that, for non-negative cosmological constant or
causal diamonds much smaller than the asymptotic radius of curvature for
negative c.c., the degrees of freedom localized in the bulk of a diamond are
constrained states of variables defined on the holographic screen. This
principle gives a simple explanation of otherwise puzzling features of BH
entropy formulae, and resolves the firewall problem for black holes in
Minkowski space. It motivates a covariant version of the CKN\cite{ckn} bound on
the regime of validity of quantum field theory (QFT) and a detailed picture of
the way in which QFT emerges as an approximation to the exact theory.
