The inertia of any particular piece of matter is attributable to the interaction between that piece of matter and the rest of the universe. A body in isolation would have zero inertia. This principle was stated by Ernst Mach in the 1870s and was made use of by Einstein in his general theory of relativity. The significance of Mach's principle in general relativity theory and the foundations of physics continues to be a contentious issue.
Subjects: Astronomy and Astrophysics — Physics.