When calculating in a rest frame, doesn't one assume both, definite velocity (zero) and position (origin)? Why is Heisenberg okay with that?
Edit: E.g. For a decay we can do calculations in which we say that the particle is truly at rest with 0 (three vector) momentum. Wouldn't that automatically mean that the particle could be literally everywhere in space? Isn't it overall a little bit troublesome, since nothing can actually really be truly at rest? So is that center of mass frame merely a good enough tool for calculation with no strict real meaning?