  We evaluate the possibility of observable effects arising from collisions
between vacuum bubbles in a universe undergoing false-vacuum eternal inflation.
Contrary to conventional wisdom, we find that under certain assumptions most
positions inside a bubble should have access to a large number of collision
events. We calculate the expected number and angular size distribution of such
collisions on an observer's "sky," finding that for typical observers the
distribution is anisotropic and includes many bubbles, each of which will
affect the majority of the observer's sky. After a qualitative discussion of
the physics involved in collisions between arbitrary bubbles, we evaluate the
implications of our results, and outline possible detectable effects. In an
optimistic sense, then, the present paper constitutes a first step in an
assessment of the possible effects of other bubble universes on the cosmic
microwave background and other observables.
