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Packet Spreading and Einstein Retardation

According to the classical special theory of relativity any nonstationary system moving with velocity $v$ must evolve (e.g., decay) $1/γ$ times slower than the system at rest, $γ=(1-v^2)^{-1/2}$ (the Einstein retardation ER). Quantum mechanics allows one to calculate the evolution of both systems separately and to compare them thus verifying ER. It is shown here that ER is not valid for a simple system: the spreading packet of the free spinless particle. Earlier it was shown that ER does not hold for some other systems. So one may state that ER is not a universal kinematic law in quantum mechanics.