  The Lorentzian Hamiltonian constraint is solved for isotropic loop quantum
cosmology coupled to a massless scalar field. As in the Euclidean case, the
discreteness of quantum geometry removes the classical singularity from the
quantum Friedmann models. In spite of the absence of the classical singularity,
a modified DeWitt initial condition is incompatible with a late-time smooth
behavior. Further, the smooth behavior is recovered only for positive or
negatives times but not both. An important feature, which is shared with the
Euclidean case, is a minimal initial energy of the order of the Planck energy
required for the system to evolve dynamically. By forming wave packets of the
matter field an explicit evolution in terms of an internal time is obtained.
