  It is argued that the symmetry algebra of asymptotically flat spacetimes at
null infinity in 4 dimensions should be taken as the semi-direct sum of
supertranslations with infinitesimal local conformal transformations and not,
as usually done, with the Lorentz algebra. As a consequence, two dimensional
conformal field theory techniques will play as fundamental a role in this
context of direct physical interest as they do in three dimensional anti-de
Sitter gravity.
