  We exploit the parallel between dynamical black holes and cosmological
spacetimes to describe the evolution of Friedmann-Lema\^itre-Robertson-Walker
universes from the point of view of an observer in terms of the dynamics of the
apparent horizon. Using the Hayward-Kodama formalism of dynamical black holes,
we clarify the role of the Clausius relation to derive the Friedmann equations
for a universe, in the spirit of Jacobson's work on the thermodynamics of
spacetime. We also show how dynamics at the horizon naturally leads to the
quantum-mechanical process of Hawking radiation. We comment on the connection
of this work with recent ideas to consider our observable Universe as a
Bose-Einstein condensate and on the corresponding role of vacuum energy.
