  We investigate the relation between vacuum energy and the hierarchy of forces
in habitable universes. The hierarchy of forces studied in \cite{fred} was
bound by $\frac{\alpha_G}{\alpha} \le 10^{-34}$, using structure formation
arguments which involve the fine structure constant $\alpha$ and the
gravitational constant $\alpha_G$. Previously we showed that the requirement of
vacuum domination epoch occuring after matter radiation equality time, places a
bound on vacuum energy in terms of the density perturbation parameter Q. Here
we impose a further condition: we require that at equality time the size of the
gas cloud which forms a galaxy at virialization time, be smaller than the
horizon size. The latter condition leads to an intriguing relation whereby
vacuum energy is bound by a power law function of the hierarchy of forces. The
constraint introduced by the hierarchy of forces on the amount of dark energy
is suggestive of an unknown microphysical mechanism that relates vacuum energy
to the other constants of nature, specifically to the gravitational and fine
structure constants and to their hierarchy.
