Dark Matter : a Challenge to Standard Gravity or a Warning ? ∗

We suggest that the conventional need for overwhelming amounts of astrophysical dark matter should be regarded as a warning to standard gravity rather than as merely a challenge to it, and show that the systematics of galactic rotation curve data can just as readily point in the direction of the equally covariant conformal gravity alternative. In particular we identify an apparent imprint of the Hubble flow on those data, something which while quite natural to conformal gravity is not at all anticipated in the standard gravitational paradigm. While the main thrust of current research is to meet the challenge of determining the precise nature and form of the dark matter which is widely thought to dominate the universe on large distance scales, nonetheless, given so startling a requirement as this, it is not inappropriate to ask whether this very need for dark matter, and in such copious proportions, might not instead be a warning that the standard Newton-Einstein theory might not in fact be the right one for gravity. Now while the standard theory was first established on solar system distance scales, for the moment its extrapolation to much larger distances is precisely just that, since there is not yet a single independent verification of Newton's Law of Gravity on galactic or larger distance scales which does not involve an appeal to dark matter, to thus show the