We apply the conformal gravity theory to a sample of 111 spiral galaxies whose rotation curve data points extend well beyond the optical disk .
With no free parameters other than galactic mass to light ratios , the theory is able to account for the systematics that is observed in this entire set of rotation curves without the need for any dark matter at all .
In previous applications of the theory a central role was played by a universal linear potential term V ( r ) = \gamma _ { 0 } c ^ { 2 } r / 2 that is generated through the effect of cosmology on individual galaxies , with the coefficient \gamma _ { 0 } = 3.06 \times 10 ^ { -30 } ~ { } { cm } ^ { -1 } being of cosmological magnitude .
Because the current sample is so big and encompasses some specific galaxies whose data points go out to quite substantial distances from galactic centers , we are able to identify an additional globally induced universal term in the data , a quadratic V ( r ) = - \kappa c ^ { 2 } r ^ { 2 } / 2 term that is induced by inhomogeneities in the cosmic background .
With \kappa being found to be of magnitude \kappa = 9.54 \times 10 ^ { -54 } ~ { } { cm } ^ { -2 } , through study of the motions of particles contained within galaxies we are thus able to both detect the presence of a global de Sitter-like component and provide a specific value for its strength .
Our study suggests that invoking dark matter may be nothing more than an attempt to describe global physics effects such as these in purely local galactic terms .