Observable Signatures of a Classical Transition
  Eternal inflation arising from a potential landscape predicts that our
universe is one realization of many possible cosmological histories. One way to
access different cosmological histories is via the nucleation of bubble
universes from a metastable false vacuum. Another way to sample different
cosmological histories is via classical transitions, the creation of pocket
universes through the collision between bubbles. Using relativistic numerical
simulations, we examine the possibility of observationally determining if our
observable universe resulted from a classical transition. We find that
classical transitions produce spatially infinite, approximately open
Friedman-Robertson-Walker universes. The leading set of observables in the
aftermath of a classical transition are negative spatial curvature and a
contribution to the Cosmic Microwave Background temperature quadrupole. The
level of curvature and magnitude of the quadrupole are dependent on the
position of the observer, and we determine the possible range of observables
for two classes of single-scalar field models. For the first class, where the
inflationary phase has a lower energy than the vacuum preceding the classical
transition, the magnitude of the observed quadrupole generally falls to zero
with distance from the collision while the spatial curvature grows to a
constant. For the second class, where the inflationary phase has a higher
energy than the vacuum preceding the classical transition, the magnitude of the
observed quadrupole generically falls to zero with distance from the collision
while the spatial curvature grows without bound. We find that the magnitude of
the quadrupole and curvature grow with increasing centre of mass energy of the
collision, and explore variations of the parameters in the scalar field
lagrangian.
