  Suppose that advanced civilizations, separated by a cosmological distance and
time, wish to maximize their access to cosmic resources by rapidly expanding
into the universe. How does the presence of one limit the expansionistic
ambitions of another, and what sort of boundary forms between their expanding
domains? We describe a general scenario for any expansion speed, separation
distance, and time. We then specialize to a question of particular interest:
What are the future prospects for a young and ambitious civilization if they
can observe the presence of another at a cosmological distance? We treat cases
involving the observation of one or two expanding domains. In the
single-observation case, we find that almost any plausible detection will limit
one's future cosmic expansion to some extent. Also, practical technological
limits to expansion speed (well below the speed of light) play an interesting
role. If a domain is visible at the time one embarks on cosmic expansion,
higher practical limits to expansion speed are beneficial only up to a certain
point. Beyond this point, a higher speed limit means that gains in the ability
to expand are more than offset by the first-mover advantage of the observed
domain. In the case of two visible domains, it is possible to be "trapped" by
them if the practical speed limit is high enough and their angular separation
in the sky is large enough, i.e. one's expansion in any direction will
terminate at a boundary with the two visible civilizations. Detection at an
extreme cosmological distance has surprisingly little mitigating effect on our
conclusions.
