The latest Scientific American, August, has an article, Is Dark Matter Real? It is not available unless you buy the magazine or pay for a download. The article is about a modified Newtonian dynamics (MOND) which has been further modified to be consistent with General Relativity. Excerpts: Astrophysicists have piled up observations that are difficult to explain with dark matter. It is time to consider that there may be more to gravity than Einstein taught us. ...Scientists can make [dark matter] simulations fit the data, but they must insert many parameters that have to be carefully chosen. Modified gravity, in stark contrast, simply predicts this correlation. … Although [MOND]works across a huge range of different galaxy types, it cannot explain the motion of galaxy clusters very well. And on the behavior of the cosmos as a whole, modified gravity is mute. Although it is mute, that doesn't mean it's wrong. It's just that there is no underlying theory yet. I always thought that the dark matter hypothesis was a bit of a kludge. Hopefully MOND is the answer.