We will have to have in our hands the full quantum theory of gravity [a combination of general relativity and quantum mechanics, yet to be understood] to find out the answer. (discovermagazine.com)
But researchers still do not know what dark matter actually is, and some have come up with new theories of gravity to explain the galaxy observations. (newscientist.com)
Theory of evolution is based on facts and is able to make predictions, much like theory of gravity. (religion.blogs.cnn.com)