  The recently measured cutoff, k_min=[4.34(+/-)0.50]/r_cmb (with r_cmb the
comoving distance to the last scattering surface), in the fluctuation spectrum
of the cosmic microwave background, appears to disfavor slow-roll inflation and
the associated transition of modes across the horizon. We show in this Letter
that k_min instead corresponds to the first mode emerging out of the Planck
domain into the semi-classical universe. The required scalar-field potential is
exponential, though not inflationary, and satisfies the zero active mass
condition, rho_phi+3p_phi=0. Quite revealingly, the observed amplitude of the
temperature anisotropies requires the quantum fluctuations in phi to have
classicalized at ~3.5x10^15 GeV, consistent with the energy scale in grand
unified theories. Such scalar-field potentials are often associated with
Kaluza-Klein cosmologies, string theory and even supergravity.
