In a hypothetical formulation, a kitten is put in a closed box with a jar of poison and a trihammer poised to smash the jar. The hammer is activated by a counter that records random events, such as radioactive decay. The experiment lasts long enough for there to be a probability of one- half that the hammer will be released. Quantum mechanics represents the system mathematically by the sum of a live-cat and a dead-cat function, each with a probability of one-half. The question is whether the act of looking ( the measurement) kills or saves the cat, since before the experimenter looks in the box both solutions are equally likely.

This light hearted example reflects a deep conceptual difficulty.