MASS AS A RELATIVISTIC QUANTUM OBSERVABLE

A field state containing photons propagating in different directions h as a non-vanishing mass which is a quantum observable. We interpret th e shift of this mass under transformations to accelerated frames as de fining space-time observables canonically conjugated to energy-momentu m observables. Shifts of quantum observables differ from the predictio ns of classical relativity theory in the presence of a non-vanishing s pin. In particular, quantum redshift of energy-momentum is affected by spin. Shifts of position and energy-momentum observables hen-ever obe y simple universal rules derived from invariance of canonical commutat ors.