Simulating the Universe(s) III: Observables for the full bubble
  collision spacetime
  This is the third paper in a series establishing a quantitative relation
between inflationary scalar field potential landscapes and the relic
perturbations left by the collision between bubbles produced during eternal
inflation. We introduce a new method for computing cosmological observables
from numerical relativity simulations of bubble collisions in one space and one
time dimension. This method tiles comoving hypersurfaces with locally-perturbed
Friedmann-Robertson-Walker coordinate patches. The method extends previous
work, which was limited to the spacetime region just inside the future light
cone of the collision, and allows us to explore the full bubble-collision
spacetime. We validate our new methods against previous work, and present a
full set of predictions for the comoving curvature perturbation and local
negative spatial curvature produced by identical and non-identical bubble
collisions, in single scalar field models of eternal inflation. In both
collision types, there is a non-zero contribution to the spatial curvature and
cosmic microwave background quadrupole. Some collisions between non-identical
bubbles excite wall modes, giving extra structure to the predicted temperature
anisotropies. We comment on the implications of our results for future
observational searches. For non-identical bubble collisions, we also find that
the surfaces of constant field can readjust in the presence of a collision to
produce spatially infinite sections that become nearly homogeneous deep into
the region affected by the collision. Contrary to previous assumptions, this is
true even in the bubble into which the domain wall is accelerating.
