  We explore the collision of two cylindrical bubbles in classical general
relativity with a scalar field stress-energy tensor. Inside each bubble the
field rests at a local minimum of the potential with non-negative energy
density. Outside the field rests at zero potential, the global minimum. The
calculation resolves the connection from the inner de-Sitter region to the
asymptotically flat Minkowski spacetime. We choose initial conditions such that
the two bubbles collide and study the full nonlinear evolution by means of a
two-dimensional numerical simulation of Einstein's equations. The collision
generates a strongly interacting region with spatially varying fields and
potentials. These circumstances promote dynamical exploration of the
potential's landscape. No horizon is present and the scalar curvature
invariants eventually diverge. We speculate that Schwarzschild-like horizons
will encompass only part of the complicated, interesting regions of spacetime
in the analogous case of colliding spherical bubbles.
