  Black hole event horizons and cosmological event horizons share many
properties, making it natural to ask whether our recent advances in
understanding black holes generalize to cosmology. To this end, we discuss a
paradox that occurs if observers can access what lies beyond their cosmological
horizon in the same way that they can access what lies beyond a black hole
horizon. In particular, distinct observers with distinct horizons may encode
the same portion of spacetime, violating the no-cloning theorem of quantum
mechanics. This paradox is due precisely to the observer-dependence of the
cosmological horizon -- the sharpest difference from a black hole horizon --
although we will argue that the gravity path integral avoids the paradox in
controlled examples.
