Take the Earth's rotation. We observe the daily progression of the sun and stars across the sky. Our ancestors believed it was the heavens that turned, not the Earth. The debate raged on. Mach's principle faced a thorny problem.
Acceleration produces inertial forces.
Einstein and others sought a mechanism to explain how a rotating body might experience a centrifugal force as a result of some sort of interaction with all the distant matter in the universe. Viewed from the roundabout, it is the rest of the universe that is rotating. We know that when electric charges circulate around a loop the resulting electric current produces a magnetic field. To test the idea, Einstein considered a small body at rest inside a rotating shell of material in otherwise empty space. Using his theory of relativity, he calculated what would happen.