Can spacetime be probed below the string size?

Strings may be explored, through a scattering process at planckian energies, down to distances of the order of the string size. We show that this is possible if the energy is not so extreme to cause a gravitational instability and when the scattering angle approaches some critical value from below. Above this angle, the distance starts increasing, thus departing from the usual position-momentum uncertainty relation, and in no instance is the resolution smaller than the string length. This suggests that below the Planck scale the very concept of space-time changes meaning. (orig.)