  I argue that scattering theory for massless particles in Minkowski space
should be reformulated as a mapping between past and future representations of
an algebra of densities on the conformal boundary. These densities are best
thought of as living on the momentum space light cone dual to null infinity,
which describes the simultaneous eigenstates of the BMS generators. The
currents describe the flow of other quantum numbers through the holographic
screen at infinity. They are operator valued measures on the momentum light
cone, with non-zero support at $P = 0$, which is necessary to describe finite
flows of total momentum, with zero energy-momentum density, on the asymptotic
holographic screen. Jet states, the closest approximation to the conventional
notion of asymptotic particle state, have finite momentum flowing out through
spherical caps of finite opening angle, with the zero momentum currents
vanishing in annuli surrounding these caps. Although these notions are valid
both in field theory and quantum gravity, I'll argue that they form the basis
for understanding the holographic/covariant entropy principle in the latter
framework, where the densities form a complete set of operators. The variables
on a finite area holographic screen are restrictions of those at infinity. The
restriction is implemented by a cutoff on the Euclidean Dirac spectrum on the
screen, which is a generalized UV/IR correspondence.
