Thoughts provoked

via An analysis of more than 70,000 galaxies demonstrates that the universe—at least up to a distance of 3.5 billion light years from Earth—plays by the rules set out 95 years ago by Albert Einstein in his General Theory of Relativity. One major implication of the new study is that the existence of dark matter is the most likely explanation for the observation that galaxies and galaxy clusters move as if under the influence of some unseen mass, in addition to the stars astronomers observe. “The nice thing about going to the cosmological scale is that we can test any full, alternative theory of gravity, because it should predict the things we observe,” says coauthor Uros Seljak, a professor of physics and of astronomy at the University of California, Berkeley, and a faculty scientist at Lawrence Berkeley National Laboratory who is on leave at the Institute of Theoretical Physics at the University of Zurich. “Those alternative theories that do not require dark matter fail these