Making the Case for Conformal Gravity
  We review some recent developments in the conformal gravity theory that has
been advanced as a candidate alternative to standard Einstein gravity. As a
quantum theory the conformal theory is both renormalizable and unitary, with
unitarity being obtained because the theory is a $PT$ symmetric rather than a
Hermitian theory. We show that in the theory there can be no a priori classical
curvature, with all curvature having to result from quantization. In the
conformal theory gravity requires no independent quantization of its own, with
it being quantized solely by virtue of its being coupled to a quantized matter
source. Moreover, because it is this very coupling that fixes the strength of
the gravitational field commutators, the gravity sector zero-point energy
density and pressure fluctuations are then able to identically cancel the
zero-point fluctuations associated with the matter sector. In addition, we show
that when the conformal symmetry is spontaneously broken, the zero-point
structure automatically readjusts so as to identically cancel the cosmological
constant term that dynamical mass generation induces. We show that the
macroscopic classical theory that results from the quantum conformal theory
incorporates global physics effects that provide for a detailed accounting of a
comprehensive set of 138 galactic rotation curves with no adjustable parameters
other than the galactic mass to light ratios, and with the need for no dark
matter whatsoever. With these global effects eliminating the need for dark
matter, we see that invoking dark matter in galaxies could potentially be
nothing more than an attempt to describe global physics effects in purely local
galactic terms. Finally, we review some recent work by 't Hooft in which a
connection between conformal gravity and Einstein gravity has been found.
