  Quadratic gravity presents us with a renormalizable, asymptotically free
theory of quantum gravity. When its couplings grow strong at some scale, as in
QCD, then this strong scale sets the Planck mass. QCD has a gluon that does not
appear in the physical spectrum. Quadratic gravity has a spin-2 ghost that we
conjecture does not appear in the physical spectrum. We discuss how the QCD
analogy leads to this conjecture and to the possible emergence of general
relativity. Certain aspects of the QCD path integral and its measure are also
similar for quadratic gravity. With the addition of the Einstein-Hilbert term,
quadratic gravity has a dimensionful parameter that seems to control a quantum
phase transition and the size of a mass gap in the strong phase.
