We outline the solution of a fundamental problem in quantum theory which has hitherto lacked a proper solution, namely, finding the requisite quantum theoretical framework guaranteeing that the calculated inverse spontaneous emission rate of a moving atom, as a composite system of charged particles interacting with the Maxwell field, is slowed down exactly as in time dilation.

• Received 25 October 2001

DOI:https://doi.org/10.1103/PhysRevLett.89.123001