Schrödinger's Cat

Definition: A thought experiment introduced by Erwin Schrödinger in 1935 to illustrate the paradox in quantum mechanics regarding the probability of finding, say, a subatomic particle at a specific point in space. According to Niels Bohr, the position of such a particle remains indeterminate until it has been observed. Schrödinger postulated a sealed vessel containing a live cat and a device triggered by a quantum event such as the radioactive decay of the nucleus. If the quantum event occurs, cyanide is released and the cat dies; if the event does not occur the cat lives. Schrödinger argued that Bohr's interpretation of events in quantum mechanics means that the cat could only be said to be alive or dead when the vessel has been opened and the situation inside it has been observed. This paradox has been extensively discussed since its introduction with many proposals made to resolve it. These paradoxes (Schrödinger's Cat and Wigner's Friend) are intended to indicate the absurdity of the overstated roles of measurement and observation in Bohr's interpretation of quantum mechanics.