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To start off, nothing about dark matter contradicts GR. All contemporary cosmological models of the Universe, which are constructed from GR, include dark matter. The "surprise" that is attributed to the discovery of dark matter involves estimates of the mass of a galaxy due to contributions from stars, gas, etc., that fall woefully short of mass estimates obtained from observations of galaxy rotation velocities (kinematics). That is, we know how much mass there is there because of our understanding of gravity, but other methods of measuring the mass don't come close to this figure. At galactic size scales GR adds virtually nothing to the Newtonian kinematics, the general relativistic corrections are substantial only when the gravitational field is very strong (e.g., binary neutron stars/black holes, very very near super massive black holes). GR is used in cosmology to model the universe on very large scales; scales so large that the "clumpy" universe that we see comprised of stars, galaxies, galaxy clusters, actually starts to look very, very smooth. Again, even within galaxy clusters, modeling the evolution of the mass in a cluster via GR doesn't change much compared with a model using Newtonian gravity. There currently exists no experiments which contradict GR, and a great amount of data (including observations of stars near the Milky Way's supermassive black hole) which directly supports it. Most people cite special relativity as the correction method behind time-dilation effects for satellites in orbit (e.g., GPS) but strictly speaking, special relativity is only completely accurate in the absence of a gravitational field. |