  We argue that in the context of string theory a large number N of connected
degenerate vacua that mix will lead to a ground state with much lower energy,
essentially because of the standard level repulsion of quantum theory for the
wavefunction of the Universe. We imagine a history where initial quantum
fluctuations give an energy density $\sim m_{susy}^2m_{Pl}^2$, but the universe
quickly cascades to an energy density $\sim m_{susy}^2m_{Pl}^2/N$. Then at
various phase transitions there are large contributions to the energy density
and rearrangement of levels, followed again by a rapid cascade to the ground
state or near it. If this mechanism is correct, the ground state of the theory
describing our world would be a superposition of a large number of connected
string vacua,with shared superselection sets of properties such as three
families etc. The observed value of the cosmological constant in terms of the
Planck mass, the scale of supersymmetry breaking and the number of connected
string vacua.
