  Critical String Theory is by definition an $S$-matrix theory. In this sense,
(quantum) gravity situations where a unitary $S$-matrix may not be a
well-defined concept, as a consequence of the existence of macroscopic (global)
or microscopic (local) gravitational fluctuations with event horizons, present
a challenge to string theory. In this article, we take some modest steps in
suggesting alternative treatments of such cases via non-critical (Liouville)
strings,which do not have a well-defined S matrix, but for which a
superscattering \$ matrix is mathematically consistent. After a brief review of
the underlying mathematical formalism, we consider a specific stringy model of
induced non-criticality, with dynamical formation of horizons, associated with
the recoil of a D-particle defect, embedded in our four-dimensional space time,
during its scattering with a (macroscopic) number of closed string states. We
study in detail the associated spacetime distortion in the neighbourhood of the
defect, which has the form of a finite-radius curved `bubble', matched with a
Minkowskian space-time in the exterior. As a consequence of the non-criticality
of the underlying sigma-model, the space time is unstable, and has non-trivial
stochastic properties: thermal properties due to its ``Rindler accelerating
nature'', and entropy growth for an asymptotic observer, associated with
information being carried away by the `recoil' degrees of freedom. We also
discuss phenomenological (and cosmological) constraints on the model.
