  The emergence of preferred classical variables within a many-body
wavefunction is encoded in its entanglement structure in the form of redundant
classical information shared between many spatially local subsystems. We show
how such structure can be generated via cosmological dynamics from the vacuum
state of a massless field, causing the wavefunction to branch into classical
field configurations on large scales. An accelerating epoch first excites the
vacuum into a superposition of classical fields as well as a highly sensitive
bath of squeezed super-horizon modes. During a subsequent decelerating epoch,
gravitational interactions allow these modes to collect information about
longer-wavelength fluctuations. This information disperses spatially, creating
long-range redundant correlations in the wavefunction. The resulting classical
observables, preferred basis for decoherence, and system/environment
decomposition emerge from the translation invariant wavefunction and
Hamiltonian, rather than being fixed by hand. We discuss the role of squeezing,
the cosmological horizon scale, and phase information in the wavefunction, as
well as aspects of wavefunction branching for continuous variables and in field
theories.
