  We give a general proof showing that once irreversible processes are
involved, a class of projective measurements is impossible. Applying this no-go
result to the Schroedinger's cat paradox implies that if something is claimed
to be a real Schroedinger's cat, there will be no measurable difference between
it and a trivial classical mixture of ordinary cats in any physically
implementable process, otherwise raising the dead will become reality. Other
similar macroscopic quantum superpositions cannot be observed either due to the
lack of non-commuting measurement bases. Our proof does not involve any quantum
interpretation theory and hypothesis.
