In theoretical physics, particularly in discussions of , Mach's principle (or Mach's conjecture) is the name given by Einstein to an imprecise hypothesis often credited to the physicist and philosopher Ernst Mach. The idea is that local inertial frames are determined by the large scale distribution of matter, as exemplified by this anecdote:
The idea regarding local inertial frames was widely supported by many, the first time Mach discussed his principle in the topic of theoretical physics.