Motivated by the result of the Michelson-Morley experiment, Albert Einstein formulated the following principle of relativity:
The laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems of co-ordinates in uniform translatory motion.
A more common formulation of this principle is the following:
All physical laws are the same in every inertial reference frame (i.e. no inertial reference frame is privileged in some way compared to other inertial reference frames).
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