In the 19th century, however, doubts are thrown on the reliability of Newton's theory. Ernst Mach criticizes Newton’s principle of inertia. He claims that the tendency of a body to continue its motion straight on is not a property of the body itself but is caused by the totality of all other bodies of the universe.

At first, Mach’s criticism is hardly noticed by the established scientific community. Starting from this criticism, however, Einstein developed his Theory of General Relativity.