<Dl> <Dd> t ′ = t − t 0 (\ displaystyle t ^ (\ prime) = t - t_ (0)) </Dd> </Dl> <Dd> t ′ = t − t 0 (\ displaystyle t ^ (\ prime) = t - t_ (0)) </Dd> <P> where r and t represent shifts in the origin of space and time, and v is the relative velocity of the two inertial reference frames . Under Galilean transformations, the time t − t between two events is the same for all inertial reference frames and the distance between two simultaneous events (or, equivalently, the length of any object, r − r) is also the same . </P> <P> Einstein's theory of special relativity, like Newtonian mechanics, assumes the equivalence of all inertial reference frames, but makes an additional assumption, foreign to Newtonian mechanics, namely, that in free space light always is propagated with the speed of light c, a defined value independent of its direction of propagation and its frequency, and also independent of the state of motion of the emitting body . This second assumption has been verified experimentally and leads to counter-intuitive deductions including: </P>

Which is the best reason for not using the family car as a reference point