  The type IIB matrix model is a promising nonperturbative formulation of
superstring theory, which may elucidate the emergence of (3+1)-dimensional
space-time. However, the partition function is divergent due to the Lorentz
symmetry, which is represented by a noncompact group. This divergence has been
regularized conventionally by introducing some infrared cutoff, which breaks
the Lorentz symmetry. Here we point out that Lorentz invariant observables
become classical as one removes the infrared cutoff and that this
"classicalization" is actually an artifact of the Lorentz symmetry breaking
cutoff. In order to overcome this problem, we propose a natural way to
"gauge-fix" the Lorentz symmetry in a fully nonperturbative manner. This also
enables us to perform numerical simulations in such a way that the
time-evolution can be extracted directly from the matrix configurations.
