Question concerns the existence of the interaction in boost operator in the instant form of relativistic dynamics. (referring to "Relativistic quantum dynamics" after E.V.Stefanovich, http://arxiv.org/abs/physics/0504062) From the existance of interactions in boosts (e.g., in instant form of dynamics) it is possible to infer, that inertial transformations in quantum systems also carry dynamical character, i.e. depend on interactions. In simpler words, the Lorentz-group transformations are only the approximations of tranformation laws for observables in INTERACTION-FREE regions. Is there any prooved experimental evidence, that in interacting quantum systems (due to the presence of interaction in boost operators in Dirac's instant form) the Lorentz transformations laws do not hold? Are there any ideas of at least theoretically feasible experiments, that can proove or refute this theory? If (!) we adopt the idea of non-validity of Lorentz transformations in the interacting systems, this (as seems to me) will mean the end of conventional QFT. This is simply because the new theory is no longer the compound of quantum mechanics and special relativity (ref. to "The quantum theory of fields" by S.Weinberg) and must no longer be called QFT. No less vital question -- is it (even theoretically) possible to build such a theory -- the theory invariant under dynamical transformation group (instead of free one)?? _________________________________________________________ Thanks everybody answering my questions here!