  Black hole horizons in equilibrium and null infinity of asymptotically flat
space-times are null 3-manifolds but have very different physical connotations.
We first show that they share a large number of geometric properties, making
them both weakly isolated horizons. We then use this new unified perspective to
unravel the origin of the drastic differences in the physics they contain.
Interestingly, the themes are woven together in a manner reminiscent of voices
in a fugue.
