Surviving in a Metastable de Sitter Space-Time
  In a metastable de Sitter space any object has a finite life expectancy
beyond which it undergoes vacuum decay. However, by spreading into different
parts of the universe which will fall out of causal contact of each other in
future, a civilization can increase its collective life expectancy, defined as
the average time after which the last settlement disappears due to vacuum
decay. We study in detail the collective life expectancy of two comoving
objects in de Sitter space as a function of the initial separation, the horizon
radius and the vacuum decay rate. We find that even with a modest initial
separation, the collective life expectancy can reach a value close to the
maximum possible value of 1.5 times that of the individual object if the decay
rate is less than 1% of the expansion rate. Our analysis can be generalized to
any number of objects, general trajectories not necessarily at rest in the
comoving coordinates and general FRW space-time. As part of our analysis we
find that in the current state of the universe dominated by matter and
cosmological constant, the vacuum decay rate is increasing as a function of
time due to accelerated expansion of the volume of the past light cone. Present
decay rate is about 3.7 times larger than the average decay rate in the past
and the final decay rate in the cosmological constant dominated epoch will be
about 56 times larger than the average decay rate in the past. This
considerably weakens the lower bound on the half-life of our universe based on
its current age.
