  In bosonic closed string field theory the "tachyon potential" is a potential
for the tachyon, the dilaton, and an infinite set of massive fields. Earlier
computations of the potential did not include the dilaton and the critical
point formed by the quadratic and cubic interactions was destroyed by the
quartic tachyon term. We include the dilaton contributions to the potential and
find that a critical point survives and appears to become more shallow. We are
led to consider the existence of a closed string tachyon vacuum, a critical
point with zero action that represents a state where space-time ceases to be
dynamical. Some evidence for this interpretation is found from the study of the
coupled metric-dilaton-tachyon effective field equations, which exhibit rolling
solutions in which the dilaton runs to strong coupling and the Einstein metric
undergoes collapse.
