  Treating the gravitational force on the same footing as the electroweak and
strong forces, we present a quantum field theory of gravity based on spin and
scaling gauge symmetries. A biframe spacetime is initiated to describe such a
quantum gravity theory. The gravifield sided on both locally flat noncoordinate
spacetime and globally flat Minkowski spacetime is an essential ingredient for
gauging global spin and scaling symmetries. The locally flat gravifield
spacetime spanned by the gravifield is associated with a noncommutative
geometry characterized by a gauge-type field strength of the gravifield. A
coordinate-independent and gauge-invariant action for the quantum gravity is
built in the gravifield basis. In the coordinate basis, we derive equations of
motion for all quantum fields including the gravitational effect and obtain
basic conservation laws for all symmetries. The equation of motion for
gravifield tensor is deduced in connection directly with the total
energy-momentum tensor. When the spin and scaling gauge symmetries are broken
down to a background structure that possesses the global Lorentz and scaling
symmetries, we obtain exact solutions by solving equations of motion for the
background fields in a unitary basis. The massless graviton and massive spinon
result as physical quantum degrees of freedom. The resulting Lorentz-invariant
and conformally flat background gravifield space-time is characterized by a
cosmic vector with a nonzero cosmological mass scale. The conformal size of the
Universe becomes singular at the cosmological horizon and turns out to be
inflationary. A mechanism for quantum inflation is demonstrated to generate the
inflation of the early Universe. Two types of gravity equation result, one is
as the extension to Einstein's equation of general relativity, and the other is
a new one that characterizes spinon dynamics.
