Originally Posted by sober

Schrodinger's Cat .
A cat is placed in a box, together with a radioactive atom. If the atom decays, and the geiger counter detects an alpha particle, the hammer hits a flask of prussic acid (HCN), killing the cat. The paradox lies in the clever coupling of quantum and classical domains. Before the observer opens the box, the cat's fate is tied to the wave function of the atom, which is itself in a superposition of decayed and undecayed states. Thus, said Schrodinger, the cat must itself be in a superposition of dead and alive states before the observer opens the box, "observes" the cat, and "collapses" its wave function. In other words, before the observer opens the box and observes the cat, the cat is BOTH dead AND alive at the same time.