  A rigorous quantum relativistic approach has been used to calculate the
relationship between the decay laws of an unstable particle seen from two
inertial frames moving with respect to each other. In agreement with
experiment, it is found that the usual Einstein's time dilation formula is
rather accurate in this case. However, small corrections to this formula were
also obtained. Although the observation of these corrections is beyond the
resolution of modern experiments, their presence indicates that special
relativistic time dilation is not rigorously applicable to particle decays.
