# Semiclassical approximation of the Wheeler-DeWitt equation - arbitrary orders and the question of unitarity. (arXiv:1802.01422v1 [gr-qc])

Wheeler-DeWitt equation of canonical quantum gravity to arbitrary orders in the

inverse Planck mass squared. We discuss in detail the origin of unitarity

violation in this scheme and show that unitarity can be restored by an

appropriate modification which requires back reaction from matter onto the

gravitational sector. In our analysis, we heavily rely on the gauge aspects of

the standard Born-Oppenheimer scheme in molecular physics.