Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...430..463w&link_type=abstract
The Astrophysical Journal, vol. 430, no. 2, pt. 1, p. 463-466
Astronomy and Astrophysics
Astrophysics
18
Dark Matter, Gravitation Theory, Gravitational Fields, Gravitational Lenses, Image Analysis, Cosmology, Deflection, Light Scattering, Newton Theory, Relativity, Space-Time Functions
Scientific paper
We present a new approach to deciding between dark matter and non-Newtonian gravity: we investigate lensing in nonstandard metric theories of gravity. In particular, we consider the properties of Weyl gravity; in this theory, point masses behave as diverging lenses with a well-defined and rather short focal length. In a universe full of such lenses, distant sources are subject to demagnification by a factor approximately 1022, and their apparent positions on the sky are largely unrelated to their true positions; the former implication excludes Weyl gravity as a variable alternative to dark matter. More generally, because there exist vast numbers of lenses at large distances from any line of sight, lensing properties offer powerful constraints on theories which seek to modify the Newtonian potential at large radii. Only two potentials (Phi = const and Phi proportional to r squared) can escape these constraints. In the context of any metric theory, we argue that the gravitational potential is Newtonian on the largest scales as well as locally, with deviations permitted only on intermediate-length scales.
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