  In applications of Einstein gravity one replaces the quantum-mechanical
energy-momentum tensor of sources such as the degenerate electrons in a white
dwarf or the black-body photons in the microwave background by c-number matrix
elements. And not only that, one ignores the zero-point fluctuations in these
sources by only retaining the normal-ordered parts of those matrix elements.
There is no apparent justification for this procedure, and we show that it is
precisely this procedure that leads to the cosmological constant problem. We
suggest that solving the problem requires that gravity be treated just as
quantum-mechanically as the sources to which it couples, and show that one can
then solve the cosmological constant problem if one replaces Einstein gravity
by the fully quantum-mechanically consistent conformal gravity theory.
