Is the usual time evolution adequate for quantum-mechanical systems? I Y. Aharonov and David Z Albert, Physical Review D 29(2), pp 223-227, 15 January 1984
Circumstances are described wherein no state at a given time (nor any definite evolutions from one time to another) can be ascribed to a given physical system, but wherein the system can nonetheless be associated with definite dispersion-free values of a new sort of observable, which we call the "multiple-time" observable. The description of physical systems in terms of these new observables is discussed. It emerges as a by-product of our work that no experiment whatever (albeit that its result is certain) can be carried out on a system without disturbing the values of other quantities.