  We present a simple argument which determines the critical value of the
anomaly coefficient in four dimensional conformal factor quantum gravity, at
which a phase transition between a smooth and elongated phase should occur. The
argument is based on the contribution of singular configurations ("spikes")
which dominate the partition function in the infrared. The critical value is
the analog of c=1 in the theory of random surfaces, and the phase transition is
similar to the Berezenskii-Kosterlitz-Thouless transition. The critical value
we obtain is in agreement with the previous canonical analysis of physical
states of the conformal factor and may explain why a smooth phase of quantum
gravity has not yet been observed in simplicial simulations. We also rederive
the scaling relations in the smooth phase in light of this determination of the
critical coupling.
