Sakharov proposed the idea of induced gravity as an alternative theory of quantum gravity. Basically, his idea is there is no need to quantize the gravitational field. He observed that many condensed matter systems give rise to emergent phenomena which are identical to general relativity quantitatively. Crystal defects can look like torsion, for example. To him, this was not a coincidence.
His idea was to start with an arbitrary background pseudo-Riemannian manifold (in modern treatments, possibly with torsion) and introduce quantum fields (matter) on it but not introduce any gravitational dynamics explicitly. This gives rise to an effective action which to one-loop order contains the Einstein-Hilbert action with a cosmological constant. In other words, general relativity arises as an emergent property of matter fields and is not put in by hand.
