Following the many-world interpretation of quantum mechanics, one can identify one-to-one a possible state of a quantum system as what the universe can be considered with a possible world. Such a state with converging to zero, but nonzero probability can be designated as almost impossible unlike those with exactly zero probability, which are quite impossible and are not considered here. The identification of ‘world’ and ‘state’ can be generalized from the many-world interpretation to quantum mechanics at all thus: The experimentally verifiable part of quantum mechanics cannot differ ‘world’ with probability one after measuring from ‘state’ with probability less than one before measuring. Quantum mechanics requires the identification of the coherent superposition of ‘states’ before measuring with the statistical ensemble of ‘worlds’ after measuring.

One can define ‘impossible world’ in quantum mechanics as a state of a quantum system and its zero or converging to zero probability. If the latter is the case, a consisting of those states set of nonzero measure can have a finite nonzero probability. One of those “almost impossible” states will happen by the probability of the whole set after measuring the quantum system. Consequently such measurement can turn an almost impossible world to real. Tunnel junction is a phenomenon, which can illustrate this. The prerequisite for it to happen is the measured state to belong to a set of nonzero measure. Nothing like this can observed in the macroscopic world where there are not such consisting of almost impossible states sets of nonzero measure.