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Dark Matter – Fact or Fantasy? | Dr. Philip Mannheim, Professor of Physics, UCONN
While there is extremely good evidence for the validity of Newton’s Law of Gravity for systems of size up to that of the solar system, the situation for much larger astronomical systems such as galaxies is not at all as clear. Specifically, the motions of galactic stars and gas far from galactic centers do not show the familiar and expected Keplerian fall off. Rather, the orbital rotational velocity curves appear to be flat in structure, leading to the suggestion that galaxies be composed predominantly of large amounts of non-luminous dark matter.
However no dark matter has yet been found despite the now 40 year astronomical, accelerator and underground searches for dark matter. We review all of these developments as well as a recent proposal by the speaker to modify gravity in a way that would eliminate the need for dark matter altogether. Further, we show that these same galactic rotation curves possess an explicit imprint due to the global cosmological Hubble flow, an imprint which is characteristic of this modified theory, and identify it as a possible manifestation of Mach’s principle, with dark matter being no more than an attempt to describe global cosmological physics in local galactic terms.
Philip Mannheim is an elementary particle theorist who pursues research in grandunification and in dynamical models of mass generation, and who has recently become involved in the explosively growing interface between particle physics and astrophysics. He is active in elementary particle theory, many body theory, astrophysics, cosmology, and general relativity. In all of his work, the notion first of maximum symmetry and then second that of symmetry breaking has been an abiding focus. Given this interest in local symmetry, it was thus natural to extend it to gravity as well, and to consider the possibility that just like the other fundamental strong, electromagnetic and weak interactions, gravity might also be a theory with dimensionless coupling constants and purely dynamical mass scales, i.e. that it might be locally conformal invariant. Given this motivation, conformal gravity theory was then explored in detail, and it was found to solve the dark matter, flatness, horizon, cosmological constant, universe age, and cosmic acceleration problems, all naturally, and all without fine tuning. More recently, the same conformal gravity theory has been shown to be consistent at the quantum level; and with it thus being both renormalizable and unitary, it is advanced as a candidate theory of quantum gravity which can serve as an alternative to string theory.